Foundations

domestic

structure SBSG

2007

ANNEX C

Small buildings structural guidance
1.A

General

1.B

Stability

1.C

Foundations

1.D

Masonry walls

1.E

Timber frame walls

1.F

Timber floor and roof members

contents

domestic

structure SBSG annex 1.A 2007

domestic

structure SBSG annex 1.A 2007

Annex
1.A
1.A.0
1.A.1
1.A.2
1.A.3
1.A.4
1.A.5

General
Introduction
Scope
Revisions to small buildings guide
New guidance
Explanation of terms
Rules of measurement for storeys, walls , panels and building heights
Contents

domestic

structure SBSG annex 1.A 2007

annex

1.A

General

1.A.0 Introduction
The Small Buildings Structural Guidance (SBSG) which is contained within Annexes 1.A-F has been
prepared to provide structural guidance to designers of small domestic buildings on how to meet
Standard 1.1.
The buildings covered by this guidance are restricted in terms of construction type, size and subsoil
conditions to those commonly occurring in Scotland.
This guidance has been written for those with expertise in building design and construction but not
necessarily in structural engineering design. Where the conditions or parameters fall outside the
scope then specialist advice should be sought from chartered engineers with the appropriate skills
and experience.
This guidance replaces the Small Buildings Guide Second Edition 1994 and has been prepared in
consultation with ODPM and DFP Northern Ireland so that reasonably uniform solutions might be
adopted towards meeting the requirements of the respective structural regulations and to incorporate
a broader base of experience into the definition of standards.
1.A.1 Scope
This guidance covers the following types of buildingsa. Buildings with masonry walls
• domestic buildings of not more than 3 storeys without basement storeys
• extensions with eaves height not more than 3m to low rise domestic buildings including
garages and outbuildings;
• single storey, single skin buildings forming a garage or outbuilding within the curtilage of a
dwelling
b. Buildings with timber frame walls
• domestic buildings of not more than 2 storeys without basement storeys
• extensions with eaves height not more than 3m to low rise domestic buildings
The full description of the types of buildings and restrictions to which this guidance is applicable is set
out within the scope of each of the annexes.
It recommended that prior to using the SBSG for particular works , the scope of the works should be
checked against all of the limitations on its use to ensure that it is appropriate in the circumstances
.and in particular :
Annex 1C: Foundations :
Geotechnical conditions
Annex 1D: Masonry walls
:
Not more than 3 storeys
Maximum building height of 15 m
Maximum 12m length between supporting walls
Wind speed verses the allowable height of building
Openings in walls not more than 3 m in length
Annex 1.E: Timber frame walls
Not more than 2 storeys
Maximum building height of 10 m
Maximum 10m length between supporting walls
Wind speed verses the allowable height of building
Openings in walls totalling not more than 30% of the wall
area
Annex 1F: Timber floor and roof members Floor spans not exceeding 5.4 m
Roof spans not exceeding 6 m
Raised Tie and Collared Roofs only for attic storage
loading

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structure SBSG annex 1.A 2007

Design and construction will also have to comply with all other relevant building standards
Annex 1.B gives general rules on stability which should be observed in Annexes 1.E-F whereas
Annexes 1.C and 1.E -F should not be used independently of each other.
1.A.2 Revisions to Small Buildings Guide
The Small Buildings Guide has been revised and updated to Small Buildings Structural Guidance
incorporating changes in construction practice specifically;
Loadings
• ‘Wind loading on traditional dwellings
‘Proposed revision of the simplified roof snow load map for Scotland
Masonry walls
• More detailed guidance on openings
• More detailed guidance on lateral support
• Differences in ground levels either sides of walls
• Stainless steel wall ties to be used in all locations
Timber Floor and Roof Members
The timber span tables have been expanded to cover raised tie and collared roofs.
1.A.3 Timber frame construction
Timber frame construction has been a significant form of construction for domestic buildings for over
20 years in Scotland ,rising from 38% of new starts in 1984 in the volume housing market to over 63
% in 2004, and a large proportion of the single build and extension market. Although the guidance in
the Small Buildings Guide was restricted to traditional masonry construction as timber frame
construction has been used and accepted for over 30 years it was considered necessary to extend
the scope of the guidance for small buildings to include timber frame walls.
The timber frame wall guidance has been restricted to masonry clad platform frame construction
which is the most common form of construction.
1.A.4 Explanation of Terms
The following terms are used in the SBSG in addition to the definitions and explanation of terms in
Appendix A of the Technical Handbooks.
Buttressing wall means a wall designed and constructed to afford lateral support to another wall
perpendicular to it, support being provided from the base to the top of the wall.
Cavity width means the horizontal distance between the two leaves of a cavity wall.
Pier means a member which forms an integral part of a wall, in the form of a thickened section at
intervals along the wall so as to afford lateral support to the wall to which it is bonded or securely tied.
Spacing means the distance between the longitudinal centres of any two adjacent timber members of
the same type, measured in the plane of floor, ceiling or roof structure of which the members form a
part.
Span means distance measured along the centre line of a member between the centres of any two
adjacent bearings or supports. Note: The spans given in Annex 1.E for Cripple Studs and Lintels and
in Annex 1.F for floor joists, and roof joists are the clear spans, i.e. spans between the faces of the
supports.
Supported wall means a wall to which lateral support is afforded by a combination of buttressing
walls, piers or chimneys acting in conjunction with floors or roof.
Engineered fill means fill that is selected, placed and compacted to an appropriate specification in
order that it will exhibit the required engineering behaviour .Normally such fill would not have taken
place prior to development of the site allowing the necessary control over the type of fill material and
method of placement to be exercised.
Non-engineered fill means fill that has arisen as a by-product of human activity, usually involving the
disposal of waste materials. Normally such fill would occur on sites where uncontrolled filling has
taken place and therefore no reliance can be placed on the type of fill material and method of
placement and hence its ability to support the buildings.

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structure SBSG annex 1.A 2007

1.A.5 Rules of measurement for storeys , walls , panels and building heights
The height of a wall or a storey should be measured in accordance with the following diagram.
line of top of gable

line of lateral
support to gable
wall along roof slope

B1

A

2.7m max

B

A1

ground level
base of wall

Top of foundations

top of
wall or
base of
parapet

H1

H2

H3

Panel height

C

HP

line of base
of gable

2.7m max

underside
of
roof
joist

line of lateral
support to gable
at ceiling level

=

Panel height

D

2.7m max

=

parapet

head binder thickness

=

=

Floor
deck
thickness

panel height
floor
deck
thickness

2.7m max

floor joist
panel height

Key
(a) Measuring storey heights
A is the ground storey height if the ground floor is a suspended timber floor or a structurally separate
ground floor slab
A1 is the ground storey height if the ground floor is a suspended concrete floor bearing on the external

wall

B is the intermediate storey height providing
B1 is the top storey height for walls which do not include a gable
C is the top storey height where lateral support is given to the gable at both ceiling level and along the
roof slope
D is the top storey height for walls which include a gable where lateral support is given to the gable
only along the roof slope
(b) Measuring wall heights
H1 is the height of a wall that does not include a gable
H2 is the height of a compartment or a separating wall which may extend to the under side of the roof.
H3 is the height for a wall(except a compartment or separating wall) which includes a gable
P is the height of a parapet. If the parapet height is more than 1.2m add the height to H1
(c) Measuring timber panel heights
Panel heights are measured from the underside of the bottom rail to the top of the top rail
(d) Measuring building height
Building heights are measured from the lowest finished ground level to the highest point of the roof

domestic

structure SBSG annex 1.B 2007

Annex
1.B
Stability
1.B.0
1.B.1
1.B.2

Introduction
Stability recommendations
Timber roof bracing

Contents

domestic

structure SBSG annex 1.B 2007

annex

1.B

Basic requirements for stability

1.B.0 Introduction
Buildings should be stable under the likely combinations of dead , imposed and wind loading
conditions in terms of the individual structural elements , their interaction together and overall stability
as a structure .
This Annex provides guidance on the principles of stability and provisions which should be taken with
respect to all forms of buildings within the scope of the SBSG.
1.B.1 Stability recommendations
The following provisions should be made to ensure the stability of the building :
a. the overall size and proportioning of the building should be limited in accordance with the specific
guidance for each form of construction;
b. a suitable layout of walls (both internal and external) forming a robust three dimensional box
structure in plan should be constructed with restrictions on the maximum size of cells measured in
accordance with the specific guidance for each form of construction;
c. the internal and external walls should be adequately connected by either masonry bonding or by
using mechanical connections;
d. the intermediate floors and roof should be of such construction and interconnection with the walls
that they provide local support to the walls and also act as horizontal diaphragms capable of
transferring the wind forces to buttressing elements of the building.
More detailed guidance is provided in Annexes 1.B-1.E
1.B.2 Timber roof bracing
Trussed rafter roofs should be braced in accordance with the recommendations of BS 5268: Part 3:
1998 .
A traditional cut timber roof (i.e. using rafters, purlins and ceiling joists) generally has sufficient built-in
resistance to instability and wind forces (e.g. from either hipped ends, tiling battens, rigid sarking, or
the like). However, diagonal rafter bracing equivalent to that recommended in BS 5268: Part 3: 1998
or Annex H of BS 8103: Part 3: 1996 for trussed rafter roofs, should be provided particularly for
single-hipped and non-hipped roofs of more than 40˚ pitch to detached houses.

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structure SBSG annex 1.C 2007

Annex
1.C

Foundations

1.C.0
1.C.1
1.C.2
1.C.3
1.C.4
1.C.5

Introduction
Conditions related to the subsoil
Design recommendations
Eccentric foundations
Extensions to existing buildings
Minimum width of strip foundations
Contents

domestic

structure SBSG annex 1.C 2007

annex

Foundations

1.C
1.C.0 Introduction
The dead , imposed and live loads are transmitted from the building to the subsoil by means of the
foundations which should be designed taking into account the loadings and the subsoil conditions
without undue settlement .
This Annex provides guidance on suitable subsoil conditions on which buildings within the scope of
the SBSG can be constructed, the precautions to be taken and guidance on simple foundations for
such buildings.
1.C.1 Conditions related to the subsoil
The subsoil conditions should be adequate where there is no • non- engineered fill or wide variation in type of subsoil within the loaded area; or
• peat within the loaded area; or
• a weaker type of soil within the loaded area at such a depth below the soil on which the foundation
rests as could impair the stability of the building
The minimum depth to the underside of foundations should be determined on the basis of the greatest
of:
• the depth to selected bearing stratum;
• a depth of 450 mm to the underside of foundations .This should avoid damage from frost action in
normal soil conditions although this depth may have to be increased in areas which are subject to
long periods of frost or in order to transfer the loading onto satisfactory ground.
• depth of 600 mm to the underside of foundations where clay soils are present although this depth
will commonly need to be increased in order to transfer the loading onto satisfactory ground.
The susceptibility of ground to movement, action of frost and changes in water table varies widely and
the advice of a structural engineer should be sought if the conditions are outwith the parameters set
out above. More detailed guidance is provided in BRE Digests 240 and 241.
1.C.2 Design recommendations
The design of foundations should be adequate where all of the following are followed a. the foundations are situated centrally under the wall( except as in clause 1.C.3);
b. the strip foundations have the minimum widths given in the table to 1.C.5;
c. concrete in chemically non-aggressive soils is composed of Portland Cement to BS EN 197-1 & 2:
2000 and fine and coarse aggregate conforms to BS EN 12620:2002 and the mix complies with
one of the following recommendations:
• in proportion of 50 kg of Portland cement to not more than 100kg
(0.05m3) of fine aggregate and 200 kg (0.1m3) of coarse aggregate, or
• Grade ST2 or Grade GEN I concrete to BS 8500-2
d. in chemically aggressive soils guidance is provided in BS 8500-1: Part 1 and
BRE Special Digest 1.
e. For strip foundations, the foundation width should not be less than the appropriate dimension , WF
in table to 1.C.5

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structure SBSG annex 1.C 2007

f.

the minimum thickness, T, of the concrete foundation is 150 mm or the scarcement width, P;
whichever is the greater, where P is derived using the table to 1.C.5 and the diagram below.
Trench fill foundations may be used as an acceptable alternative to strip foundations.
g. footings with regular offsets should have a depth at least 1.33 times the respective projection P1
(see diagram 1.7.2 opposite); with the overall width not less than the sum of , WF from table to
1.C.5 plus offset dimensions A1 and A2 and walls should be central on the foundation
h. for foundations stepped in elevation
• height of steps, S, should not be of greater height than the foundation thickness, T
• overlap, L, should be the greater of twice the step height ,S, the foundation thickness, T, or 300
mm

P
.

WT

.

P

.

P

.

A1

WT

A2

P

.

P1
1.33 P1 min
.

.

L

T

WF + A1 + A2

WF

i.

S

T

T

L = greater of 2 x S, T, 300mm

foundations for piers , buttresses and chimneys should project as shown in the diagram below
where X must be not less than P

X
X

P

X

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structure SBSG annex 1.C 2007

1.C.3 Eccentric foundations
a. This guidance and the diagram opposite is limited to:
• single storey buildings of 4.5 m maximum height
where a wall is to be constructed either against a
boundary or against an existing wall where it is not
possible to construct the wall centrally on the
foundation.
• masonry cavity or timber frame walls with masonry
outer leaf with either a flat or pitched roof
• similar good ground conditions below both the
existing and new foundations
• the foundations should comply with all of the clauses
of this Annex (i.e. minimum foundation depth
thickness and width ,concrete grade (Grade ST2 or
GEN I) and the range of normal subsoil conditions
stated) .
b. Where the wall and its foundation is to be constructed
against an existing wall then the foundation should
comply with 1.C. 4 below

c. the full width of the foundation, WF (from Table 1.C.5) is
not effective in transmitting the load to the soil, and only
a proportion of the width is effective. This effective width
of the foundation, WF' is determined from
WF' = WF – (2 × e)
where e is the eccentricity of the resultant thrust R due
to the wall load, about the centre-line of the foundation.
d. Nonetheless, the minimum foundation width,WF, should
still be read directly from Table 1.C.5.
e. the minimum foundation thickness, T for the minimum
foundation widths listed in Table 1.C.5 should be taken
as 200mm.
f. an appropriate steel reinforcement mesh, (e.g. A142),
should be placed at 50mm cover from the base of the
foundation.

.

WT

e

R
T
WF'
WF

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structure SBSG annex 1.C 2007

1.C.4 Extensions to existing buildings
a. This guidance and the diagram opposite is limited to:
• extensions of not more than two storeys connected to
existing buildings
• extensions with masonry cavity or timber frame walls with
masonry outer leaf with either a flat or pitched roof
• similar ground conditions below both the existing and new
foundations in range types I-VI from Table to 1.C.5
• the extension foundations should comply with all of the
clauses of this Annex (i.e. minimum foundation depth
thickness and width ,concrete grade (Grade ST2 or GEN
I) and the range of normal subsoil conditions stated) .
b. Where the depth of the existing foundations is less than that
in 1.C.1, the depth of the extension foundation should
match that of existing foundation depth at the interface and
step down progressively to that of 1.C.1.
e. To minimise the occurrence of differential settlement
between the extension and the existing structure, the
following should be considered;
• movement joints should be placed between the existing
and new foundations, and walls to accommodate any
differential settlement between the extension and
existing building .
• on non-compressible soils and rock (Soil types I, II and
III in Table 1.C.5) the strip foundation widths listed in the
table should be adopted and the new foundation should
be placed at the same depth as the existing foundation,
• On soils of medium compressibility (Soil types IV, V and
VI in Table 1.C.5) the foundation dimensions should be
large enough so that excessive settlement is avoided by
increasing the minimum width ,WF, by 25% from the
values listed in Table 1.C.5 to lower the bearing
pressure on the soil, recognising that foundations on soil
types V and VI do not fall within the provisions of this
annex if the total load exceeds 30 kN/m.
• To reach less compressible soil, the new foundation
may be placed at a greater depth than the existing
foundation. In such a case extreme care must be taken
to ensure that stability of the existing foundation is
maintained during excavation for the new foundation.
• The design of an appropriate foundation on highly
compressible soils (Soil type VII in Table 1.C.5) is
beyond the scope of this annex and specialist advice
should be sought for such cases.
• Additional information is provided in BRE GBG 53
Foundations for low-rise building extensions
• Where the subsoil to the existing building has been
subjected to ground improvement techniques ( e.g.
vibrocompaction , underpinning , soil replacement etc )
then specialist advice should be sought from chartered
engineers with the appropriate skills and experience.

existing
walls
new wall

floor

movement joint between
existing and new walls
and foundations

existing
foundation

new foundation
for extension

existing wall
movement joint
new wall

New Walls

Existing Wall

Brick ties and
channels allowing
vertical movement

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structure SBSG annex 1.C 2007

1.C.5 Minimum width of strip foundations
The recommended widths of foundations set out in the table below may be used subject to :
• the subsoil conditions in 1.C.1,
• the foundation design provisions in 1.C.2
• the type and condition of subsoil is known and is within the types set out in the Table below,
• the loading at the base of the wall is within acceptable limits.
The table is applicable only within the strict terms of the criteria described within it and where the
subsoil is not covered by the types set out below or the total load from the load-bearing walling
exceeds 70kN/linear metre or 30kN/linear metre in types of subsoil under heads V-VI or type VII
subsoil below, then a designed foundation may be required and the advice of a structural engineer
should be sought.
Minimum width of strip footings
Total load of load-bearing walling not
more than (kN/linear metre)
Condition Field Test Applicable
Type of
20
30
40
50
60
70
of ground
Ground
Minimum width of strip foundation,
(including
WF (mm)
engineered
fill)
Requires at least a pneumatic In each case equal to the width of wall
I Rock
Not
inferior to or other mechanically operated
sandstone pick for excavation
,limestone
or
firm
chalk
II Gravel or
Medium
Requires pick for excavation. 250
300
400
500
600
650
Sand
dense
Wooden peg 50mm square in
cross section hard to drive
beyond 150mm
III Clay
Stiff
Can be indented slightly by 250
300
400
500
600
650
Sandy Clay Stiff
thumb
IV Clay
Firm
Thumb makes impression 300
350
450
600
750
850
Sandy Clay Firm
easily
600
V Sand
Loose
Can be excavated with a 400
Silty sand
Loose
spade. Wooden peg 50mm
Note
Clayey sand Loose
square in cross section can be
Foundations on soil types
easily driven
V and V1 do not fall
VI Silt
Soft
Finger pushed in up to 10mm
450
650
within the provisions of
Clay
Soft
this annex if the total load
Sandy clay Soft
exceeds 30kN/m.
Clay or silt
Soft
Finger easily pushed in up to
Refer to specialist advice
Very soft
VII Silt
25mm
Very soft
Clay
Sandy clay Very soft
Very soft
Clay or silt

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structure SBSG annex 1.D 2007

Annex
1.D
Masonry walls
1.D.0
Introduction
1.D.1
Wall types
1.D.2
Conditions relating to the Building of which the walls forms part
1.D.3
Maximum floor area
1.D.4
Imposed loads on roofs , floors and ceilings
Thickness of walls
1.D.5
General
1.D.6
Solid external walls, compartment walls and separating walls in coursed brickwork or
blockwork
1.D.7
Solid external walls, compartment walls and separating walls in uncoursed stone , flints
etc
1.D.8
Cavity walls in coursed brickwork and blockwork
1.D.9
Walls providing vertical support to other walls
1.D.10 Internal load-bearing walls in brickwork or blockwork
1.D.11 Parapet walls
1.D.12 Single leaf external walls
1.D.13 Modular bricks and bricks
1.D.14 Maximum height of buildings based on wind loadings
1.D.15 Maximum allowable length and height of the wall
Construction materials and workmanship
1.D.16 Wall ties
1.D.17 Brick and block construction
1.D.18 Compressive strength of masonry units
1.D.19 Declared compressive strength of masonry units
1.D.20 Normalised compressive strength of masonry units
1.D.21 Compressive strength of masonry units in walls
1.D.22 Mortar
1.D.23 Lintels for openings
Loading on walls
1.D.24 Maximum span of floors
1.D.25 Other loading conditions
End restraint
1.D.26 Vertical lateral restraint to walls
1.D.27 Criteria for buttressing walls
1.D.28 Criteria for piers and chimney providing restraint
Openings , recesses , chases and overhangs
1.D.29 General
1.D.30 Dimensional criteria for openings and recesses
1.D.31 Sizes of openings and recesses
1.D.32 Chases
1.D.33 Overhangs
1.D.34 Lateral support by roofs and buildings
1.D.35 Gable wall strapping
1.D.36 Interruption of lateral support
1.D.37 Movement in masonry
Small single storey , single skin buildings
1.D.38 General
1.D.39 Size and proportions of openings
1.D.40 Wall thicknesses and piers
1.D.41 Horizontal lateral restraint at roof level
1.D.42 Proportions for masonry chimneys
Contents

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structure SBSG annex 1.D 2007

annex

1.D

Masonry walls

1.D.0 Introduction
Small buildings of traditional masonry walls can be designed to take advantage of custom and
practice to provide designs taking into account loading conditions , limitations on dimensions ,
openings and subject to , restraint conditions .
This Annex provides guidance for traditional masonry wall construction for the following building types
a. domestic buildings of not more than 3 storeys where loading criteria for individual floors does not
exceed those given in 1.D.4 and total limit of loading does not exceed that given in 1.D.25;
b. single storey single skin extensions to domestic buildings including garages and outbuildings that
do not exceed the dimensional criteria set out in 1.D.2b ; and.
d. single storey , single skin buildings forming a garage or outbuilding within the curtilage of a
dwelling that do not exceed the dimensional criteria set out in 1.D.2c
1.D.1 Wall types
This Annex deals only with the types of wall extending to full storey height set out below and parapet
walls.
a. Domestic buildings of up to 3 storeys
• External walls
• Internal load bearing walls
• Separating walls
b. Extensions to domestic buildings and single storey buildings
• External walls
• Internal load bearing walls
This annex should be used in conjunction with Annexes 1.B ;and
a. if wall thickness is to be determined according to 1.D.5 to 1.D.13 all appropriate design conditions
given in this Annex should be satisfied;
b. walls should comply with the relevant requirements of BS 5628: Part 3: 2001, except as regards
the conditions given in 1.D.2 and 1.D. 3 -4,1.D.14-41;
c. in formulating the guidance of this Annex, the worst combination of circumstances likely to arise
was taken into account.
d. If a requirement of this Annex is considered too onerous in a particular case then adequacy by
calculation should be shown in respect of the aspect of the wall which is subject to the departure
rather than for the entire wall;
e. the guidance given in this Annex is based upon unit compressive strengths of bricks and blocks
being not less than that indicated in the Tables to 1.D.19-20 and diagrams to 1.D.21
f. BS5628 Part 1; 1992 gives design strengths for walls where the suitability for use of masonry
units of other compressive strengths are being considered.

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structure SBSG annex 1.D 2007

1.D.2 Conditions relating to the Building of which the walls forms part
This Annex applies only to buildings having proportions within the following limits and as shown
on the Diagrams below subject to the limits of 1.D.15
a. domestic buildings of not more than three storeys
• the maximum height of the building measured from the lowest finished ground level
adjoining the building to the highest point of any wall or roof should not be greater than
15 m ;
• the height of the building H, should not exceed twice the least width of the building W 1 ,
•

the height of the wing H 2 should not exceed twice the least width of the wing W 2 when
the projection P exceeds twice the width W 2 .
Minimum width

Maximum height

H
not to
exceed
15m

H

H

W1

lowest
ground level

W1
W1 not to be less
than 0.5H

H2

W1

P1

W2

b. Size of extensions to domestic buildings
For extensions, height H should not exceed the relevant limits shown below (see also 1.D.38)
where H is measured from the top of the foundation or from the underside of the floor slab
where this provides effective lateral restraint.

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structure SBSG annex 1.D 2007

Domestic
building

domestic
building

4.5m max

3.0 m max

extension

3.0m max

= =

Maximum roof
slope 40

c. Size of single storey , single skin buildings
Small single-storey , single skin buildings the height H of the building should not exceed 3m and W
(the length or width whichever is more ) shall not exceed 9m (see also 1.D.38) where H is
measured from the top of the foundation or from the underside of the floor slab where this
provides effective lateral restraint

3.0 m max

II
II

3.6 m max

3.0 m max

Maximum roof
slope 40

1.D.3 Maximum floor area
The guidance in this annex applies where 1. Floors enclosed by structural walls on all sides do not exceed 70 m2; and
floors without a structural wall on one side do not exceed 36 m2

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structure SBSG annex 1.D 2007

Area not
exceeding
36 m2

Area not
exceeding
36 m2
Area not
exceeding
36 m2

Area not
exceeding
36 m2

Area not
2
exceeding 70 m

Area not
2
exceeding 70 m
Area not
2
exceeding 70 m

1.D.4 Imposed loads on roofs , floors and ceilings
The imposed loads on roofs, floors and ceilings should not exceed those given in the table below.
Element
Roof

Loading
distributed load:

1.00 kN/m2 for spans up to 12 metres
1.50 kN/m2 for spans up to 6 metres

Floors

distributed load:

2.00kN/m2 together with a concentrated
load of 1.4 kN

Ceilings

distributed load:

0.25 kN/m2 together with concentrated
load: 0.9 kN

The guidance for snow loading in 1.F.6 applies only to a free standing flat roofed structure with
no parapet and with the roof on one level only, provided that there are no other buildings within
1.5m of its perimeter.

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structure SBSG annex 1.D 2007

Thickness of walls
1.D.5 General
Wall thickness should be determined according to this Annex provided the following conditions
are meta. relating to the building of which the wall forms a part in 1.D.2-4 and 1.D.14 (3.4 , 3.15 to 3.17);
and
b. relating to the wall in 1.D.15-41 (3.18 to 3.41).
Wall thicknesses may be affected by adequate bearing for precast concrete units.
Conditions – building
a. limitations
on
size
and
Conditions
relating
to
proportions
of
building
and
parts
of
building of which wall
building
(
1.D.2
)
forms part
b. max allowable floor areas (
1.D.3)
c. max imposed and wind loads (
1.D.4 and 1.D.14)

Outside
Annex
1.D scope

N

Are building
satisfied?

conditions

Yes

Conditions relating to
wall

Outside Annex
1.D scope

Are
wall
satisfied ?

conditions

Yes

Use 1.D.6-13 for
thickness assessment

wall

Conditions – wall
a. max allowable length and
height of wall ( 1.D.15)
b. construction materials and
workmanship ( 1.D.16-23)
c. loading on walls ( 1.D.24-25)
d. end restraints ( 1.D.26-28)
e. openings , recesses ,
overhangs, chases (1.D.2933)
f.
lateral support by floors and
roofs (1.D.34-36)
g. movement in masonry (1.D.37)
h. conditions relating to external
walls of small single storey
buildings and extensions (
1.D.38-41)

domestic

structure SBSG annex 1.D 2007

1.D.6 Solid external walls, compartment walls and separating walls in coursed brickwork or
blockwork
Solid walls constructed of coursed brickwork or blockwork should be at least as thick as 1/16 of
the storey height. Further requirements are given in the table below.
Height of wall
Length of wall
Minimum thickness of wall
not exceeding
not exceeding 12m
190mm for the whole of its height
3.5m
exceeding 3.5m
not exceeding 9m
190mm for the whole of its height
but not
exceeding 9m but not
290mm from the base for the height of one storey,
exceeding 9m
exceeding 12m
and 190mm for the rest of its height
exceeding 9m
not exceeding 9m
290mm from the base for the height of one storey,
but not
but not exceeding 12m and 190mm for the rest of its height
exceeding 12m
exceeding 9m but not
290mm from the base for the height of two storeys,
exceeding 12m
and 190mm for the rest of its height.
1.D.7 Solid external walls, compartment walls and separating walls in uncoursed stone,
flints etc
The thickness of walls constructed in uncoursed stone or bricks or other burnt or vitrified material
should not be less than 1.33 times the thickness required by 1.D.6.
1.D.8 Cavity walls in coursed brickwork and blockwork
All cavity walls should have leaves at least 90 mm thick and structural cavities at least 50 mm wide.
The wall ties should have a horizontal spacing of 900mm and a vertical spacing of 450mm, which is
equivalent to 2.5 ties per square metre. Wall ties should also be provided, spaced not more than
300mm apart vertically, within a distance of 225mm from the vertical edges of all openings, movement
joints and roof verges. For selection of wall ties for use in a range of cavity widths refer to Table to
1.D.16. For specification of cavity wall ties refer to paragraph 1.D.16.
For external walls, compartment walls and separating walls in cavity construction, the combined
thickness of the two leaves plus 10 mm should not be less than the thickness required by 1.D.6 for
a solid wall of the same height and length.
1.D.9 Walls providing vertical support to other walls
Irrespective of the materials used in the construction, a wall should not be less in thickness than
any part of the wall to which it gives vertical support.
1.D.10 Internal loadbearing walls in brickwork or blockwork
With the exception of compartment walls or separating walls internal loadbearing walls should have
a thickness not less than :
(specified thickness from 1.D.6) /2 less 5 mm
except for a wall in the lowest storey of a three storey building carrying load from both upper storeys,
which should have a thickness as determined by the above equation or 140 mm, whichever is the
greater.

domestic

structure SBSG annex 1.D 2007

1.D.11 Parapet walls
The minimum thickness and maximum height of parapet walls should be as given in the table and
diagrams below only where access is limited ( e.g. for occasional maintenance ).
Cavity wall
Max
(mm)

parapet

600

height

H

t

Thickness(mm)

t1+t2 not more than 200

t1
t2

Hp

860

Solid wall

t1+t2 more than 200

T

600

t = 150

760

t = 190

level of junction
of wall and
structural roof

860
t = 215
Note that t must not be more than T
level of junction
of wall and
structural roof

1.D.12 Single leaf external walls
The single leaf of external walls of small single storey non-domestic buildings and of extensions
need be only 90 mm thick, provided the requirements of 1.D.38-41 are met.
1.D.13 Modular bricks and blocks
Where walls are constructed of bricks or blocks having modular dimensions derived from BS 6649 1985 wall thicknesses recommended in this Annex which derive from a dimension of a brick or
block may be reduced by an amount not exceeding the deviation from work size permitted by a
British Standard relating to equivalent sized bricks or blocks made of the same material.

domestic

structure SBSG annex 1.D 2007

1.D.14 Maximum height of buildings based on wind loadings
The maximum height of building which should be adequate for the various site exposure conditions
and wind speed should be derived by following the procedure which is set out on the Flow Chart
below using the map of wind speeds , topographic zone diagrams below and tables 1 and 2 enabling
the maximum height of building to be read off table 3 opposite
This design guidance has been revised in accordance with Wind loading on Traditional dwellings and
is based on BS 6399: Part 2 1997 using hourly mean wind speeds and it should be noted that the
wind speeds are derived from a different basis than in the Small Buildings Guide and it is important
that they are only applied to the methodology within this annex.
Flow chart for deriving maximum allowable building height

Read
windspeed
,V from
map above

Topographic
zone
from
above
diagrams

Read
Factor ,T
from
Table 1

Factor
A from
table 2

Wind
direction

Factor
S=
VxTxA

Z2

0.25Lu

Z1

Z2

0.4Lu 0.4 Lu

0.25Lu

Max
allowable
building
height
from
Table 3

Z3
1.2 L u

Lu

Hills and ridges

Z2
Wind
direction 0.4 L u
0.4 L u
Lu

Z1

Z2
0.4 Ld
0.4 L d
Ld

Cliffs and escarpments
Map of wind speeds ( m/sec)

Topographic zones for Table 1

domestic

structure SBSG annex 1.D 2007

Table 1
Factor T
Topographic category and
average slope of whole
hillside,
ridge,
cliff
or
escarpment
Category 1: Nominally flat
terrain, average slope < 1/20

Table 2
Factor A
Site Altitude Factor A
(m)

Factor T
Zone
2
1.0

Zone
3
1.0

Category 2: Moderately steep
1.24
1.13
terrain, average slope < 1/5
Category 3: Steep terrain,
1.36
1.20
average slope > 1/5
Note:
Outside of these zones factor T = 1.0

1.10

Table 3
Factor
S
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40

Zone
1
1.0

0
50
100
150
200
300
400

1.15

Maximum allowable building height (m)
Country Sites

1.00
1.05
1.10
1.15
1.20
1.30
1.40

Town Sitesa

Distance to the coastb

Distance to the coastb

<10km

10 to 50km

>50km

<10km

10 to 50km

>50km

15
15
11
8
6
4.5
3.5
3

15
15
14.5
10.5
8.5
6.5
5
4
3.5
3

15
15
15
13
10
8
6
5
4
3.5
3

15
15
15
15
15
13.5
11
9
8
7
6
5
4
3

15
15
15
15
15
15
13
11
9.5
8.5
7.5
7
6
5.5
4.5
4
3

15
15
15
15
15
15
14.5
12.5
10.5
9.5
8.5
8
7
6
5.5
5
4
3

Notes
a. For sites on the outskirts of towns not sheltered by other buildings use the values for country sites
b. Where a site is nearer than 1 km to an inland area of water which extends more than 1 km in the
wind direction , the distance to the coast should be taken as from the edge of the water.

domestic

structure SBSG annex 1.D 2007

1.D.15 Maximum allowable length and height of the wall
This annex does not deal with walls longer than 12 m, measured from centre to centre of buttressing
walls, piers or chimneys providing restraint, or of walls exceeding 12 m in height. (See also table to
1.D.6 and 1.D.37 regarding movement joints )
Construction materials and workmanship
1.D.16 Wall ties
Wall ties should comply with BS EN 845-1 and be material references 1 or 3 in BS EN 845 Table
A1 austenitic stainless steel or suitable non-ferrous ties. Wall ties should be selected in
accordance with the following table

Cavity wall ties
Permissible type of tie
Normal cavity
width (mm)

(Note 1)

Tie length (mm)

(Note 2)

BS EN 845-1 tie (Note 4)

50 to 75
200
Types 1, 2, 3 or 4 to DD 140-2* and selected on the basis
76 to 90
225
of the design loading and design cavity width
91 to 100
225( Note 3)
*Although DD 140-2 was withdrawn on 1 February 2005,
101 to 125
250
the tie user classes (types) given in Tables 1 and 3 of the
126 to 150
275
latter document can continue to be used after this date.
151 to 175
300
176 to 300
(See Note 2)
Notes
1 Where face insulated blocks are used the cavity width should be measured from the face of the
masonry unit.
2 The embedment depth of the tie should not be less than 50mm in both leaves. For cavities wider
than 180mm calculate the length as the structural cavity width plus 125mm and select the nearest
stock length.
3 Double triangle ties having a strength to satisfy Type 2 of DD 140-2*, are manufactured. Specialist
tie manufacturers should be consulted if 225mm long double triangle format ties are needed for 91 to
100mm cavities.
4
Reference requires to be additionally made to DD 140-2* for the selection of the type (i.e. types
1, 2, 3 or 4) relevant to the performance levels given in DD140-2.
1.D.17 Brick and block construction
Walls should be properly bonded and solidly put together with mortar. Materials should be chosen
from the following list as being suitable for their intended use and for the exposure conditions,
likely to prevail a. clay bricks or blocks to BS 3921: 1985 or BS EN 771-1; or
b. calcium silicate bricks to BS 187: 1978 or BS 6649: 1985; or BS EN 771-2 or
c. concrete bricks or blocks to BS 6073: Part 1: 1981; or BS EN 771-3 or 4 or
d. square dressed natural stone to the appropriate requirements described in BS 5628-3 or BS
EN 771-6 ; or
Manufactured Stone to BS 6457: 1984 or BS EN 771-5.
1.D.18 Compressive strength of masonry units
The minimum compressive strength requirements for masonry units according to BS Standards and
BS EN Standards are given in the Diagrams in 1.D.21 where the masonry units indicated for
Conditions A, B and C should have declared compressive strengths of not less than the values given
in the Table below. Normalised compressive strengths for block sized clay and calcium silicate
masonry units not complying with brick dimensional format are given in the Table to 1.D.20.

domestic

structure SBSG annex 1.D 2007

Any unit complying with BS EN
771-5 will be acceptable for
conditions A, B and C

1.D.19 Declared Compressive Strength of Masonry Units complying with BS EN 771 - 1 to 5
(N/mm2)
Manufactured
Autoclaved
Masonry Clay masonry units Calcium
Silicate Aggregate
aerated conc. Stone Masonry
Unit
to BS EN 771-1
masonry units to Concrete
Masonry units units to BS EN
Masonry
BS EN 771-2
to BS EN 771-5
Units to BS
771-4
EN 771-3
Condition A
Brick
Group 1 Group 2 Group 1 Group 2
6.0
9.0
6.0
9.0
6.0
2.9
Block
See clause 1.D.20
2.9*
Condition B
Brick

Group 1
9.0

Group 2
13.0

Block

Group 2 Group 1
13.0
9.0
See clause 1.D.20

Condition C
Brick
Group 1
18.0
Block

Group 2 Group 1
25.0
18.0
See clause 1.D.20

Group 2
25.0

9.0
7.3*

7.3

18.0
7.3*

7.3

Notes
1. This table applies to Group 1 and Group 2 units.
2. For the EN 771 series of standards for masonry units the values of declared compressive
strengths (N/mm2) are mean values.
3. Brick: a masonry unit having work sizes not more than 337.5 mm in length or 112.5 mm in
height.
4. Block: a masonry unit exceeding either of the limiting work sizes of a brick and with a minimum
height of 190mm. For blocks with smaller heights, excluding cuts or make up units, the strength
requirements are as for brick except for solid external walls where the blocks should have a
compressive strength at least equal to that shown for block for an inner leaf of a cavity wall in the
same position.
5. Group 1 masonry units have not more than 25% formed voids (20% for frogged bricks). Group 2
masonry units have formed voids greater than 25%, but not more than 55%
6. Refer to 1.D.21 for locations of Conditions A, B and C
7. Values marked * are dry strengths to BS EN 772-1
1.D.20 Normalised compressive strength of masonry units of clay and calcium silicate blocks
complying with BS EN 771 - 1 and 2 (N/mm2)
Standard
Clay masonry units to
BS EN 771-1 Calcium
silicate masonry units
to BS EN 771-2

Condition

Group 1 masonry units

Group 2 masonry units

A

5.0

8.0

B

7.5

11.0

C

15.0

21.0

Notes:
1 Values in this Table are normalised compressive strengths (N/mm2). Compressive strengths of
masonry units should be derived according to EN 772-1.
2 The Table applies to clay and calcium silicate block masonry units where the work size is more
than 337.5mm in length or 112.5mm in height.
3 Group 1 masonry units have not more than 25% formed voids (20% for frogged bricks). Group 2
masonry units have formed voids greater than 25%, but not more than 55%.

domestic

structure SBSG annex 1.D 2007

1.D.21 Compressive strengths of masonry units in walls

underside
of
structural
roof

HS

Top of
structural floor

S

S

Underside
of
structural
roof

HS

Hf

Cavity
wall

Internal
wall
Underside
of
structural
floor

Cavity
wall

Where
Hf Less than or equal to 1mCondition A
Where
Hf greater than 1mCondition B

Top of
structural
floor

This wall to be at least
140 mm thick in blockwork or
215 mm thick in brickwork below
groundfloor level if
height Hf exceeds 1m.

HS

Underside
of structural
floor

HS

Topside of
structural
floor

Internal
wall
Underside
of
structural
roof

This wall to
be at least
140mm thick
blockwork or
215mm thick
brickwork

Notes
1. If HS is not more than 2.7 m , the compressive strength of bricks or blocks should be used in walls as
indicated by the key
2.If HS is more than 2.7m, the compressive strength of bricks or blocks used in the wall should be at
least Condition B, or as indicated by the key whichever is the greater.
3.If the external wall is solid construction the masonry units should have a compressive strength of at
least that shown for the internal leaf of a cavity wall in the same position.
The guidance in the diagram for walls of two or three storey buildings should only be used to determine
the compressive strength of the masonry units where the roof construction is of timber.

domestic

structure SBSG annex 1.D 2007

1.D.22 Mortar
Mortar should be a. Mortar designation (iii) according to BS 5628:Part 3:2001;
b. Strength class M4 according to BS EN 998 - 2 ;
c. 1:1: 5 or 6 CEM 1, lime and fine aggregate measured by volume of dry materials
1.D.23 Lintels for openings
Proprietary steel or concrete lintels suitable for use with masonry cavity wall construction should be
tested by a notified body or justified by calculations
Loading on walls
1.D.24 Maximum span of floors
The maximum span for any floor supported by a wall is 6 m, where the span is measured centre
to centre of bearing as shown on the diagrams below.
Floor member bearing on
Wall

Floor member bearing on
joist hanger
wall

floor

floor

floor span
maximum 6m

floor span
maximum 6m

centre line
of bearing

centre line
of bearing

Loading on walls
1.D.25 Other loading conditions
a. Vertical loading on walls should be distributed. This may be assumed for concrete floor slabs,
precast concrete floors, and timber floors designed in accordance with annex 1.F, and where the
bearing length for lintels is 150 mm or greater. Where a lintel has a clear span of 1200 mm or less
the bearing length may be reduced to 100 mm. Where lintels carry a concrete floor the bearing
length should be at least 150mm or L/10 whichever is the greater, where L is the span of the lintel.
b. Differences in level of ground or other solid construction between one side of the wall and the
other should be less than four times the thickness of the wall and the combined dead and imposed
load should not exceed 70kN/m at base of wall as shown below provided there is a full storey
height of masonry above the upper retained level.
c. Walls should not be subject to lateral load other than from wind, and that covered by 1.D.25 b

domestic

structure SBSG annex 1.D 2007

a. Examples of ground level differences
Ground
Supported
floor slab
Retained
height

t1

t2

Suspended
ground floor
Void

Retained
height

W

H should be less
than or equal to
1m and less than
or equal to
4( t1+ t2)

W
To be level for
a distance of not
less than 1.25H

Suspended
ground floor

Retained
height
W

W

b. Maximum differences in ground level
t

Retained
height

t

H should be less
than or equal to 1m
and less than
or equal to 4t
H

Retained
height

H should be less
than or equal to 1m
and less than or
equal to 4t
H

Concrete fill
to wall cavity

W
W
Notes
Floor slabs in diagrams b have been omitted for clarity and may be on either side of the walls shown.
Cavity walls should be tied in accordance with Table to clause 1.D.16.
These recommendations apply only to circumstances where there is a full storey height of masonry above
the upper retained level.

End restraint
1.D.26 Vertical lateral restraint to walls
The ends of every wall, except single leaf walls less than 2.5 m in height and length in small single
storey non-domestic buildings and extensions should be bonded or otherwise securely tied
throughout their full height to a buttressing wall, pier or chimney. Long walls may be provided with
intermediate support dividing the wall into distinct lengths; each distinct length is a supported wall for
the purposes of this part. The buttressing wall, pier or chimney should provide support from the base
to the full height of the wall.

domestic

structure SBSG annex 1.D 2007

1.D.27 Criteria for buttressing walls
The diagram below gives certain rules for buttressing walls. Additionally i f the buttressing wall is
not itself a supported wall, its thickness T2 should not be less than a. half the thickness required by this part for an external or separating wall of similar height and
length, less 5 mm; or
b. 75 mm if the wall forms part of a dwelling and does not exceed 6 m in total height and 10 m in
length; or
c. 90 mm in any other case.
Notes
1. The buttressing wall should be bonded or
securely tied to the supported wall and
at the other end to a buttressing wall,
pier or chimney.
2. The length, LB, of the buttressing wall
should be at least 1/6 of the overall
height, H, of the supported wall.
3. The position and shape of the openings
should not impair the lateral support to
be given by the buttressing wall.
4. Openings or recesses in the buttressing
wall more than 0.1 m2 should be at least
550mm from the supported wall.

Openings in a buttressed wall

LB
Buttressing
Wall
Supported
wall

T2

H

550mm

5. There may be only one opening or recess not more than 0.1 m2 at any position.
6. The opening height in a buttressed wall should be not more than 0.9 times the floor to ceiling
height and the depth of lintel including any masonry over the opening should be not less than 150
mm.
Refer to diagram to 1.A.5 for the rules for measuring the height of the supported wall.

1.D.28 Criteria for piers and chimney
providing restraint
1. Piers should measure at least three
times the thickness of the supported
wall, and chimneys twice the thickness,
measured at right angles to the wall.
Piers must have a minimum width of
190 mm as shown opposite.
2. The sectional area on plan of chimneys
(excluding openings for fireplaces and
flues) should be not less than the area
required for a pier in the same wall, and
the overall thickness should not be less
than twice the required thickness of the
supported wall
3. The buttressing wall, pier or chimney
should provide support to the full height
of the wall from base to top of wall.

centre line of
buttressing wall centre line of
pier(alternative
T
arrangement)
centre line
of chimney

Buttressing
wall
Pier

H
Chimney
min
190mm

centre line
of pier

domestic

structure SBSG annex 1.D 2007

Openings , recesses , chases and overhangs
1.D.29 General
The number, size and position of openings and recesses should not impair the stability of a wall or
the lateral support afforded by a buttressing wall to a supported wall. Construction over openings
and recesses should be adequately supported.
1.D.30 Dimensional criteria for openings and recesses
The dimensional criteria are given in the diagram and table below.
No openings should be provide in walls below ground floor except for small holes for services and
ventilation etc. which should be limited to a maximum area of 0.1 m2 at not less than 2 m centres .
1.D.31 Sizes of openings and recesses
corner of two
external walls

H

Opening Opening
W1
W2
P1
P2
P3

Recess
W3

Opening
W4 P5

P4

outer face of
return w all

Notes
1. W1 + W2 + W3 should not exceed 2L/3
2. None of W1 or W2 or W3 should exceed 3m
3. P1 should not be greater than W1/X
4. P2 should not be greater than or equal to W1/X
5. P3 should be greater than or equal to (W2+
W3)/X
6. P4 should be greater than or equal to W3/X

7. P5 should be greater than or equal to W4/X
but should not be less than 665 mm.
8. The value of Factor X should be taken from
the table below or can be given the value 6,
provided the compressive strength of the
bricks or blocks (in the case of a cavity wall,
in the loaded leaf) is not less than 7 N/mm2.

Value of factor 'X' (see diagram above)
Nature of roof
span

Maximum roof
span (m)

Minimum
thickness of
wall inner
(mm)

Span of floor
is parallel to
wall

Span of
timber floor
into wall

Span of
concrete floor
into wall

Max
4.5m

Max
4.5m

Max
6.0m

Max
6.0m

Value of factor 'X'
roof
spans
parallel to wall

non applicable

timber
roof
spans into wall

9

100

6

6

6

6

6

90

6

6

6

6

5

100

6

6

5

4

3

90

6

4

4

3

3

domestic

structure SBSG annex 1.D 2007

1.D.32 Chases
Chases should not a. if vertical, be deeper than 1/3 of wall thickness or, in cavity walls, 1/3 of leaf thickness ;
b. if horizontal, be deeper than 1/6 of the thickness of the leaf or wall; and
c. be so positioned as to impair the stability of the wall, particularly where hollow blocks are used.
1.D.33 Overhangs
In constructing a corbelled overhang, the amount of any projection should not impair the stability
of the wall.
Minor overhangs may occur at the interfaces between different masonry materials which have minor
differences in thickness provided this does not impair the stability of the wall.
1.D.34 Lateral support by roofs and floors
The walls in each storey of a building should extend to the full height of that storey, and have
horizontal lateral supports to restrict movement of the wall at right angles to its plane.
Floors and roofs should a. act to transfer lateral forces from walls to buttressing walls, piers or chimneys; and
b. be secured to the supported wall by connections specified in clauses 1.D.34-35 .
The requirements for lateral support of walls at roof and floor levels are given in the table below and
guidance on satisfying the requirements is given in clauses 1.D35 and 1.D.36
Wall Type

Wall Length
any length

Solid or cavity: external
compartment separating
greater than 3 m
internal load-bearing wall
(not being a compartment or
separating wall)

any length

Lateral support required
roof lateral support by every roof forming
a junction with the supported wall
floor lateral support by every floor
forming a junction with the supported
wall
roof or floor lateral support at the top of
each storey

Walls should be strapped to floors above ground level, at intervals not more than 2 m by tension
straps as shown below to BS EN 845-1. For corrosion resistance purposes , the tension straps
should be material reference 14 or 16.1 or 16.2 (galvanised steel) or other more resistant
specifications including material references 1 or 3 (austenitic stainless steel). The declared tensile
strength of tensions straps should not be less than 8 kN

domestic

structure SBSG annex 1.D 2007

30x5mm galvanised mild
steel or other durable strap
at least 1200mm long and
held tight against masonry
wall

30 x 5mm galvanised mild
steel or other durable strap
held tight against masonry
wall and fixed across 3 joists

Dwangs minimum 38mm
width to extend
at least ½ depth of joist

internal leaf of external cavity
wall requiring lateral restraint

Tension strap detail 1

Tension strap detail 2

Tension straps need not be provided a. in the longitudinal direction of joists in domestic
buildings of not more than two storeys, if the joists are
at not more than 1.2 m centres and have at least 90
mm bearing on the supported walls or 75mm bearing
on a timber wall- plate at each end ,and
b. in the longitudinal direction of joists in domestic
buildings of not more than two storeys, if the joists
are carried on the supported wall by joist hangers in
accordance with BS EN 845-1 of the restraint type
described in BS 5628:Part 1 and shown opposite and
are incorporated at not more than 2 m centres;

Restraint type joist hanger
X to be not less than 90mm

c. where a concrete floor has at least 90 mm bearing on
the supported wall as opposite;
d. where floors are at or about the same level on
each side of a supported wall and contact
between the floors and wall is either continuous
or at intervals not exceeding 2m. Where contact
is intermittent, the points of contact should be in
line or nearly in line on plan as shown on the
diagrams below.

X

X

Restraint by concrete floor or roof

domestic

structure SBSG annex 1.E 2007

Restraint of internal walls

Where joists are not hard up to
the wall blockings at not greater
than 2m centres should be used
at the same locations on both
sides of the wall

1.D.35 Gable wall strapping
Gable walls should be strapped to roofs as shown
opposite by tension straps as shown in the diagrams
opposite .
Vertical strapping at least 1m long should be provided at
eaves level at intervals not exceeding 2m if the roof a. has got a pitch of 150 or less;
b. is not tiled or slated;
c. is not of a type known by local experience to be
resistant to wind gusts; and
d. has not got main timber members spanning onto the
supported wall at not more than 1.2 m centres.

Tension straps
at highest point
If H is greater
that will provide a than 16t, provide
secure connection restraint here
at not greater
Tension straps
than 2m centres
at not more than
2 metre centres
X X/2
ss
kne
hic0mm
t
of s + 1
su m
ve
a
=
e
l
t of

X/2

h

Gable
end
wall

Tension strap location
Effective strapping at gable

Vertical strapping at eaves

dwang

Strap turned
over uncut
block

pack

strap anchored
to wall and rafter

Vertical strapping at eaves

Rafter fixed to Each joist fixed to wall-plate
wall plate with With framing anchors
framing anchor Or skew nails
or truss clip

Strap anchored to
wall and turned
over wall plate

domestic

structure SBSG annex 1.E 2007

1.D.36 Interruption of lateral support
Where a stair or other opening in a floor or roof adjoins a supported wall and interrupts the continuity
of lateral supporta. the length of the opening should be not more than 3 m, measured parallel to the supported wall;
b. where a connection is provided by means other than by anchor, this should be provided
throughout the length of each portion of the wall situated on each side of the opening;
c. where connection is provided by anchors, these should be spaced closer than 2 m on each side
of the opening to provide the same number of anchors as if there were no opening; and
d. there should be no other interruption of lateral support.
1.D.37 Movement in masonry
Max spacing of movement joints
Clay brickwork
Calcium silicate brickwork
Concrete brickwork and blockwork

12 m centres
7.5 m centres
6 m centres

Reference should be made to BS 8103-2, Annex B Code of practice for masonry walls for housing
which provides general guidance for movement joints.

domestic

structure SBSG annex 1.E 2007

External walls of small single storey single skin buildings and extensions
1.D.38 General
The guidance given applies in the following circumstances:2
a. The floor area of the building or extension does not exceed 36m
b. The walls are solidly constructed in brickwork or blockwork using materials which comply with
clauses 1.D.16-1.D.23.
2
c. Where the floor area of the building or extension exceeds 10m ,the walls have a mass of not less
2
2
than 130 kg/m . (Note: There is no surface mass limitation recommended for floor areas of 10m or
less.)
d. Access to the roof is only for the purposes of maintenance and repair.
e. The only lateral loads are wind loads.
f. The maximum length or width of the building or extension does not exceed 9m.
g. The height of the building or extension does not exceed the lower value derived from the Diagrams
to clause 1.D.2.
h. The roof is braced at rafter level, horizontally at eaves level and at the base of any gable by roof
decking, rigid sarking or diagonal timber bracing, as appropriate, in accordance with BS 5268: Part 3.
i. Walls are tied to the roof structure vertically and horizontally in accordance with clauses 1.D.34-36
and with horizontal lateral restraint at roof level in accordance with clause 1.D.41.
j. The roof structure of an extension is secured to the structure of the main building at both rafter and
eaves level.
1.D.39 Size and proportions of openings
One or two major openings not more than 2.1m in height are permitted in one wall of the building or
extension only. The width of a single opening or the combined width of two openings should not
exceed 5m.
The only other openings permitted in a building or extension are for windows and a single leaf door.
The size and location of these openings should be in accordance with the diagram below.
Notes
1. Major openings should be restricted to
one wall only. Their aggregate width
should be not more than 5.0m and their
height should not be more than 2.1m
2. There should be no other openings within
2.0m of a wall containing a major opening.
3. The aggregate size of openings in a wall
not containing a major opening should be
not more than 2.4m2.
4. There should not be more than one
opening between piers.
5. Unless there is a corner pier the
distance from a window or a door to a
corner should not be les s than 390 mm.

No other openings in this zone

2.0m

390mm min

390mm min

Wall with major
openings
Isolated column

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structure SBSG annex 1.E 2007

1.D.40 Wall thicknesses and piers
The walls should have a minimum thickness of 90mm.
The minimum pier size ( AP x BP) should be 390mm x 190mm or 327mm x 215mm depending on the
size of the masonry units
Isolated columns should be 325mm x 325mm minimum (CC x CC )
Walls which do not contain a major opening but exceed 2.5m in length or height should be bonded or
tied to piers for their full height at not more than 3m centres as shown in the diagram below
Wall without a major opening
BP

3.0m max

AP

AP

90mm min

3.0m max

3.0m max

Walls which contain one or two major openings
should in addition have piers as shown in the
Diagrams above and opposite. Where ties are
used to connect piers to walls they should be
flat, 20mm x 3mm in cross section, be in
stainless steel in accordance with clause
1.D.16, be placed in pairs and be spaced at
not more than 300mm centre vertically

Wall with a single major opening
BP

AP

G
Dotted line
indicates range
of wall positions

BP

AP

G > 2.5m

AP
G

2.5m

BP

Wall with two major openings

BP

AP

Dotted line indicates
range of wall positions
CC

CC

domestic

structure SBSG annex 1.E 2007

1.D.41 Horizontal lateral restraint at roof level
Walls should be tied horizontally at no more than 2m centres
to the roof structure at eaves level, base of gables and along
roof slopes with straps fixed in accordance with clauses
1.D.34 and 1D.35 and where straps cannot pass through a
wall they should be adequately secured to the masonry using
suitable fixings and isolated columns should also be tied to
the roof structure all as shown below. Fixings should be in
accordance with the diagram opposite.

1.D.42 Proportions for Masonry Chimneys
Where a chimney is not adequately supported by ties or securely restrained in any way, its height if
measured from the highest point of intersection with the roof surface, gutter, etc should not exceed
4.5W, provided the density of the masonry is greater than 1500 kg/m3 where W is the least horizontal dimension of the chimney measured at the same point of intersection; and
H is measured to the top of any chimney pot or other flue terminal.
H

H
W

W
Level of highest
point of
intersection

domestic

structure SBSG annex 1.F 2007

Annex
1.E Timber frame walls
1.E.0
Introduction
1.E.1
Wall types
1.E.2
Conditions relating to the Building of which the walls forms part
1.E.3
1.E.4
1.E.5
1.E.6
1.E.7
1.E.8
1.E.9
1.E.10
1.E.11
1.E.12
1.E.13
1.E.14
1.E.15
1.E.16
1.E.17
1.E.18
1.E.19
1.E.20
1.E.21
1.E.22
1.E.23
1.E.24
1.E.25
1.E.26
1.E.27
1.E.28
1.E.29
1.E.30
1.E.31
1.E.32
1.E.33
1.E.34
1.E.35
1.E.36
1.E.37
1.E.38
1.E.39
1.E.40
1.E.41
1.E.42
1.E.43
1.E.44
1.E.45
1.E.46
1.E.47
1.E.48
1.E.49

Maximum floor area
Imposed loads on roofs , floors and ceilings
Wall structure
General
Minimum thickness of external walls
Walls providing vertical support to other walls
Timber frame wall sizing
Site data
Building data
Horizontal loads
Wall sheathing
Site data and building data
Altitude/distance category
Length/width ratio
Racking bands
Percentage openings
Masonry cladding arrangements
Panel sheathing and nailing
Vertical loads
Wall stud sizing
Cripple stud sizing
Lintel sizing
Example
Overall stability
Maximum allowable length and height of wall
Construction materials and workmanship
General
Wall ties
Masonry cladding
Brick and block construction
Mortar
Lintels for masonry cladding
Timber members
Wall sheathing
Fasteners
Fabrication
Composite action
Wall panel connections
Nailing and fixing schedule
Loading on walls
Maximum span of floors
Other loading conditions
End restraint
Openings, notching and drilling
General
Framing of openings
Dimensional criteria for openings
Small unframed openings
Notching and drilling
Lateral support by roofs and floors
Differential movement

domestic

structure SBSG annex 1.F 2007

annex

1.E

Walls in certain small buildings – timber frame

1.E.0 Introduction
Small buildings of masonry clad platform frame construction can be designed to provide designs
taking into account loading conditions , limitations on dimensions , openings and subject to , restraint
conditions .
This structural guidance for timber frame construction for small buildings is intended to be similar to
that for masonry construction restricted to cover a limited range of timber frame wall dimensions,
member sizes and loading conditions which commonly apply in Scotland.
To comply with the philosophy of the Small Buildings Structural Guidance, the guidance for timber
frame construction has been produced for use by those who have expertise in building design and
construction but not necessarily in structural engineering design. Where the conditions or parameters
fall outside the scope then specialist advice should be sought from chartered engineers with the
appropriate skills and experience.
This guidance is based on the Platform Frame method of timber frame construction with external
masonry cladding being the most common form of timber frame construction in Scotland It is
restricted to the member sizes and types and sheathing materials which are commonly used in small
buildings in Scotland.
It should be noted that the guidance within this Annex only relates to Section 1 Structure. There are
other factors such as cavity barriers, breather membranes ,thermal insulation, etc which may be
relevant and reference should be made to the appropriate sections in the Technical Handbooks.
Timber frame construction outwith the parameters and materials covered in this guidance should be
designed in accordance with the guidance in BS 5268 Part 6.1 1996.
This Annex provides guidance for timber frame wall construction for the following building types
a. domestic buildings of not more than 2 storeys where loading criteria for individual floors does not
exceed those given in 1.E.4 and total limit of loading does not exceed that given in 1.E.41;
There is guidance in Annex 1.D: Masonry walls which is relevant to this annex with respect to
masonry cladding to timber frame walls.
1.E.1 Wall types
This Annex deals only with the types of wall extending to full storey height set out below.
a. Domestic buildings of not more than 2 storeys
• External walls
• Internal load bearing walls
• Compartment walls
• Separating walls
This Annex should be used in conjunction with Annexe 1.B ; and
a. if a timber wall structure is designed in accordance with the guidance in Annex 1.E, all
appropriate design conditions should be satisfied;
b. walls should comply with the relevant recommendations of BS 5268: Part 6.1: 1996, except as
regards the conditions given in 1.E.2,1.E.3-4 and 1.E.8-49
c. in formulating the guidance of this Annex, the worst combination of circumstances likely to
arise was taken into account.
d. If a recommendation of this Annex is considered too onerous in a particular case then
adequacy by calculation should be shown in respect of the aspect of the wall which is
subject to the departure rather than for the entire wall;
e. the guidance given in this Annex is based upon the material strengths of timber , sheathing ,
plasterboard and masonry being not less than that indicated in 1.E.27-39
f. roof construction should be :
• duo or mono pitch trussed rafters with 15-45o pitch and dead weight not more than 1.036
kN/m2 on the slope

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structure SBSG annex 1.F 2007

• or flat ,raised tie or collared roofs in accordance with guidance in Annex 1.F.
g. floor dead load should be not more than 0.5 kN/m2
h. Internal , party and external wall dead loads should be not more than 1.5 kN/m excluding
masonry cladding
i. panel heights should be not more than 2.7 m
j. timber frame walls act should compositely with the masonry cladding ,sheathing and inner
plasterboard lining all contributing to the racking resistance of the timber frame walls.
This guidance does not cover hipped ends to roofs with girder trusses which impose point loads on to
the walls or other situations where point loads occur.
Wall sheathing which provides the racking resistance to wind loading generally is the limiting factor
and this aspect should be checked prior to carrying the remainder of the design. It is unlikely that this
guidance could be used with walls with openings more than 30 % of the total wall area or for front
gable buildings where there are large percentage openings in the shorter length walls.
1.E.2 Conditions relating to the Building of which the walls forms part
This Annex applies only to buildings having proportions within the following limits and as shown
on the Diagrams below subject to the limits of 1.E.26
The maximum height of the building measured from the lowest finished ground level adjoining
the building to the highest point of any wall or roof must not be greater than:
ƒ
10 m for duo pitch roofs
ƒ
5.5 m for mono pitch or flat roofs
• the height of the building H, should not exceed twice the least width of the building W 1 ,
the height of the wing H 2 should not exceed twice the least width of the wing W 2 when the
projection P exceeds twice the width W 2 .
Maximum height

Minimum width

H
not to
exceed
10m

H

H

lowest
ground level

W1

W1
W1 not to be less
than 0.5H

H2

W1

P1

W2

1.E.3 Maximum floor area
The guidance in this annex applies where •
Floors enclosed by structural walls on all sides do not exceed 70 m2; and
•
floors without a structural wall on one side do not exceed 36 m2

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structure SBSG annex 1.F 2007

Area not
exceeding
36 m2

Area not
2
exceeding 70 m

Area not
exceeding
36 m2

Area not
2
exceeding 70 m
Area not
2
exceeding 70 m

Area not
exceeding
36 m2

Area not
exceeding
36 m2

1.E.4 Imposed loads on roofs , floors and ceilings
The imposed loads on roofs, floors and ceilings should not exceed those given in the table below.
Element

Loading

Roof

distributed load:

1.00 kN/m2 for spans up to 12 metres
1.50 kN/m2 for spans up to 6 metres

Floors

distributed load:

2.00kN/m2 together with a concentrated load of 1.4
kN

Ceilings

distributed load:

0.25 kN/m2 together with concentrated load: 0.9 kN

The guidance for snow loading in 1.F.6 applies only to a free standing flat roofed structure with no
parapet and with the roof on one level only, provided that there are no other buildings within 1.5m
of its perimeter.

domestic

structure SBSG annex 1.F 2007

Wall structure
1.E.5 General
Wall structure should be determined according to this Annex provided the following conditions are
meta.
relating to the building of which the wall forms a part (1.E.2); and
b. relating to the wall 1.E.3-49

Conditions relating to
building of which wall
is part

Outside
Annex 1.E
scope

No

Are
building
conditions satisfied ?

Yes

Outside
Annex 1.E
scope

Conditions – building
d. limitations on size and proportions of
building and parts of building ( 1.E.2, )
e. max allowable floor areas ( 1.E.3)
f.
max imposed and wind loads (
1.E.12.)

No
Are wall conditions
satisfied?

Yes

Conditions – wall
i.
max allowable length and height of
wall ( 1.E.26)
j.
construction materials and
workmanship ( 1.E.27-39)
k. loading on walls ( 1.E.40 and 1.E.41)
l.
end restraints ( 1.E.42)
m. openings, notching and drilling
(1.E.43-47)
n. lateral support by floors and roofs
(1.E.48)
o. Differential movement (1.E.49)

Use Annex 1.E for
timber frame walls

1.E.6 Minimum thicknesses of external cavity walls
Masonry clad timber frame walls should comprise masonry cladding for at least 100 mm thick ,50 mm
nominal cavity width 9mm nominal sheathing thickness and timber studs at least 89 mm depth and
plasterboard inner wall lining . Wall ties should be securely nailed to the vertical studs and not to the
sheathing alone generally at the following spacings
a. Brickwork cladding: horizontal spacing of 600mm and a vertical spacing of 375mm
b. Blockwork cladding : horizontal spacing of 400 or 600mm and a vertical spacing of 450mm,
c. Wall ties should also be provided, spaced not more than 300mm apart vertically, within a distance
of 225 mm from the vertical edges of all openings, movement joints and roof verges.
d. In exposed wind locations, the tie density would require to be increased in accordance with BS
5268 -6.1:1996.
e. For specification of cavity wall ties refer to 1.E.28
1.E. 7 Walls providing vertical support to other walls
Irrespective of the materials used in the construction, a wall should not be less in thickness than
any part of the wall to which it gives vertical support.

domestic

structure SBSG annex 1.F 2007

1.E.8 Timber frame wall sizing
The following procedure which should be followed to determine the member sizing etc for masonry
clad timber frame wall construction which should be adequate for a particular location depending on
the building dimensions and the site exposure conditions is based on BS 5268-6.1
The procedure is summarised in the flow chart below and explained in detail thereafter together with a
worked example in 1.E.24.
Design Procedure Flow Chart
Assess Building Data( 1.E.10)

Length / Width ratio (1.E.11

Assess Site Data( 1.E.12)

Wall Sheathing Requirements(1.E.13-18)

Horizontal(Wind) Loads (1.E.19)

Vertical(Snow ) Loads ( 1.E20)

Wall Stud Requirements ( 1.E.21)

Cripple Stud Requirements(1.E.22)

Lintel requirements (1.E.23)

domestic

structure SBSG annex 1.F 2007

1.E.9 Wall sheathing
The horizontal loads arising from wind action are resisted and transferred to the base of the walls by
the racking resistance of the racking ( or wind) wall panels .
Walls should only be considered to be Racking Walls and hence able to provide resistance to wind
action if they are specifically designed in accordance with the following racking procedure and have at
least one layer of OSB3 or plywood sheathing secured to the timber studs.
The Flow Chart below and subsequent clauses provide guidance on how to provide adequate racking
resistance by means of racking or wind walls comprising wall sheathing and nailing arrangements ..
Racking Procedure Flow Chart

Building and Site Data including assessing β = B/A (1.E.10-12)
Read off Altitude-Distance Category from Table to 1.E.13

Read Racking Band from Tables to 1.E.14

Assess the percentage openings in each wall of Building(1.E.15)

Assess the Masonry Cladding Arrangement from Table to 1.E.16

Select Panel Sheathing and Nailing requirements (1.E.17)

Use of internal racking walls, if appropriate (1.E.17)

domestic

structure SBSG annex 1.F 2007

Building dimensions
1.E.10 Building Data stage 1
Assess the following dimensions for the
building :
• Overall outside plan width , A
• Overall outside plan length, B
• Height from ground level to eaves ,H
• Overall Building Height from ground
level to ridge
• Number of storeys
• Roof shape :- duopitch , monopitch or
flat
Duo pitch roof
• Spans of roof and floors

Key
A : Building Width (smaller dimension of
the building cross-section (plan)
B : Building Length (larger dimension of the
building cross-section (plan)
β: Length/ Width Ratio of the building
plan
β = B/A.

RA

H

Mono pitch roof

A
B
RB

Flat roof

Plan

1.E.11 Length/width ratio stage 2
Determine the length/ width ratio, β in accordance with the diagram above
Note that β should always be rounded up from the derived value to the nearest 0.5 and will be not
less than 1.0 in any case.

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structure SBSG annex 1.F 2007

1.E.12 Site Data stage 3
a. Determine the site location of the building under consideration
b. Assess the distance of the site to the coast within the following ranges
• Not more than 10 km
• not more than 100 km
• greater than 100 km
Where a site is nearer than 1 km to an inland area of water which extends more than 1 km in the
wind direction , the distance to the coast should be taken as from the edge of the water.
c. Assess the altitude of the site above ordinance datum within the following ranges
• 0m
• not more than 50 m
• not more than 100m
• not more than 150m
• not more than 200m
• not more than 300m
• not more than 400 m
d. Determine the snow zone as A or B from the snow map below
Determine the wind speed from the wind speed map below
Snow Zone Map

Wind Speed Map ( m/s)

Zone
A
B

Inverness

domestic

structure SBSG annex 1.F 2007

Table Altitude/distance category
1.E.13 Altitude/distance category stage 4
Using the Site Altitude and Distance to the coast,
Distance to the coast(km)
Altitude
read the Altitude-Distance category (AD1-AD6) from
<10
<100
>100
the table opposite
0m
AD1
AD1
AD1
< 50m
AD1
AD1
AD1
Key
< 100m
AD2
AD2
AD2
AD1-AD6 :Altitude / Distance to the coast Category
<
150m
AD3
AD3
AD3
< : less than
<
200m
AD4
AD3
AD3
< : not more than
< 300m
AD5
AD5
AD4
< 400m
AD6
AD6
AD5
1.E.14 Racking Bands stage 5
The Racking Band is the wind force on to an external wall panel in a parallel direction to that panel as
shown in the diagram in clause 1.E.10 and can be read from the relevant table below using the
following information derived above
• Building height H, and roof type from clause 1.E.10
• Length/width ratio, β from clause 1.E.11
• Wind speed from clause 1.E.12
• Altitude / distance, AD, category from clause 1.E.13
Tables 1-4 provide racking bands for duo pitch roofed buildings for heights of 5.5 and 10 metres
height for wind speeds of 30, 27, 25 and 23 metres / sec
Table 5-8 provide racking bands for duo pitch roofed buildings for heights of 5.5 metres height for
wind speeds of 30, 27, 25 and 23 metres / sec
Table 9-12 provide racking bands for duo pitch roofed buildings for heights of 5.5 metres height for
wind speeds of 30, 27, 25 and 23 metres / sec
Racking Bands for Duopitch roofs
Table 1 Wind speed = 30m/s
5.5 m Height
10m Height
β
Side
Altitude/Distance Category (AD)
Altitude/Distance Category (AD)
AD1 AD2 AD3 AD4 AD5 AD6 AD7 AD1 AD2 AD3 AD4 AD5 AD6 AD7
1
A
R3
R3 R3 R4 R4
R5 R5 R5
R6 R8 R9 R11
B
R3
R3 R3 R3 R4
R4 R5 R7
R8 R9 R11 R11
1.5
A
R6
R6 R7 R8 R9 R11 R11
B
R2
R2 R2 R3 R3
R3 R3
2
A
R8
R9 R11 R11 R11
B
R1
R1 R2 R2 R2
2.5
A
R11 R11 R11
B
R1
R1 R1
3
A
R11 R11
B
R1
R1
3.5
A
R11
B
R1
4
A
B
-

domestic

structure SBSG annex 1.F 2007

Racking Bands for Duopitch roofs
Table 2 Wind speed = 27m/s
5.5 Height
Altitude/Distance Category (AD)
β
Side
AD1 AD2 AD3 AD4 AD5 AD6 AD7
1
A
R2
R2 R3 R3 R3
R4 R4
B
R2
R2 R2 R3 R3
R3 R4
1.5
A
R5
R5 R6 R6 R7
R8 R9
B
R1
R2 R2 R2 R2
R2 R3
2
A
R7
R7 R8 R9 R11 R11 R11
B
R1
R1 R1 R1 R2
R2 R2
2.5
A
R8
R9 R11 R11 R11 B
R1
R1 R1 R1 R1
3
A
R9
R11 R11 R11 B
R1
R1 R1 R1 3.5
A
R11 R11 R11 B
R1
R1 R1 4
A
R11 R11 B
R1
R1 -

10m Height
Altitude/Distance Category (AD)
AD1 AD2 AD3 AD4 AD5 AD6 AD7
R4
R5 R6 R7 R9
R11 R6
R6 R7 R8 R9
R11 R11 R11 R4
R5 -

Racking Bands for Duopitch roofs
Table 3 Wind speed = 25m/s
5.5 Height
Altitude/Distance Category (AD)
Sid
β
AD AD AD AD
AD AD
e
1
2
3
4
5
6
1
A
R2
R2
R2
R2
R3
R3
B
R2
R2
R2
R2
R3
R3
1.5 A
R4
R4
R5
R5
R6
R7
B
R1
R1
R1
R2
R2
R2
2
A
R5
R6
R7
R7
R8
R9
B
R1
R1
R1
R1
R1
R1
2.5 A
R7
R7
R8
R9
R11 R11
B
R1
R1
R1
R1
R1
R1
3
A
R8
R8
R9
R11 R11 R11
B
R1
R1
R1
R1
R1
R1
3.5 A
R8
R9
R11 R11 R11 B
R1
R1
R1
R1
R1
4
A
R9
R11 R11 R11 B
R1
R1
R1
R1
-

10m Height
Altitude/Distance Category (AD)
AD AD AD AD AD AD
1
2
3
4
5
6
R4
R4
R5
R6
R7
R9
R5
R5
R6
R7
R7
R8
R11 R11 R11 R3
R4
R4
-

AD
7
R3
R3
R7
R2
R11
R2
R11
R1
-

AD
7
R11
R9
-

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structure SBSG annex 1.F 2007

Racking Bands for Duopitch roofs
Table 4 Wind speed = 23m/s
5.5 Height
Altitude/Distance Category (AD)
β
Side AD1 AD2 AD3 AD4 AD5 AD6
1
A
R1 R2
R2 R2
R2 R2
B
R1 R1
R2 R2
R2 R2
1.5 A
R3 R3
R4 R4
R5 R5
B
R1 R1
R1 R1
R1 R2
2
A
R4 R5
R5 R6
R7 R7
B
R1 R1
R1 R1
R1 R1
2.5 A
R5 R6
R6 R7
R8 R9
B
R1 R1
R1 R1
R1 R1
3
A
R6 R7
R7 R8
R9 R11
B
R1 R1
R1 R1
R1 R1
3.5 A
R7 R7
R8 R9
R11 R11
B
R1 R1
R1 R1
R1 R1
4
A
R7 R8
R9 R11 R11 R11
B
R1 R1
R1 R1
R1 R1

AD7
R3
R2
R6
R2
R8
R1
R11
R1
R11
R1
R11
R1
-

Racking Bands for Monopitch roofs
Table 5 Wind speed = 30m/s
5.5 Height
Altitude/Distance Category (AD)
β Side AD1 AD2 AD3 AD4 AD5 AD6
1
A
R5 R6
R6 R7
R8 R8
B
R3 R3
R3 R4
R4 R4
1.5 A
R11 R11 R11 B
R2 R2
R2 2
A
B
2.5 A
B
-

Table 6 Wind speed = 27m/s
5.5 Height
Altitude/Distance Category (AD)
AD7 AD1 AD2 AD3 AD4 AD5 AD6
R9 R4
R5 R5
R6 R6
R7
R5 R2
R2 R3
R3 R3
R3
R8
R9 R9
R
R11 R1
R2 R2
R2 R2
R11 R11 R1
R1 -

Racking Bands for Monopitch roofs
Table 7 Wind speed = 25m/s
5.5 Height
β=
Altitude/Distance Category (AD)
(B / Side
A)
AD1 AD2 AD3 AD4 AD5 AD6
1
A
R3 R4
R4 R5
R5 R6
B
R2 R2
R2 R2
R3 R3
1.5 A
R7 R7
R8 R9
R1- R11
B
R1 R1
R1 R2
R2 R2
2
A
R9 R11 R11 R11 B
R1 R1
R1 R1
2.5 A
R11 R11 B
R1 R1
3
A
R11 B
R1 3.5 A
B
4
A
B
-

10m Height
Altitude/Distance Category (AD)
AD1 AD2 AD3 AD4 AD5 AD6
R3
R3 R4
R5 R6 R7
R4
R4 R5
R5 R6 R7
R8
R9 R9
R11 R11 R3
R3 R3
R4 R4 R11 R11 R2
R2 -

AD7
R9
R8
-

AD7
R8
R4
-

Table 8 Wind speed = 23m/s
5.5 Height
Altitude/Distance Category (AD
AD7
R6
R3
R11
R2
-

AD1
R3
R1
R5
R1
R7
R1
R9
R1
R11R1
R11
R1
R11
R1

AD2
R3
R1
R6
R1
R8
R1
R9
R1
R11
R1
R11
R1
-

AD3
R3
R2
R6
R1
R9
R1
R
R1
R11
R1
-

AD4
R4
R2
R7
R1
R
R1
R11
R1
-

AD5
R4
R2
R8
R1
R11
R1
-

AD6
R5
R2
R9
R2
R11
R1
-

AD7
R5
R3
R
R2
-

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structure SBSG annex 1.F 2007

Racking Bands for Flat roofs
Table 9 Wind speed = 30m/s
5.5 Height
Altitude/Distance Category (AD)
β Side AD1 AD2 AD3 AD4 AD5 AD6
1
A
R4
R5
R5
R6
R6
R7
B
R4
R5
R5
R6
R6
R7
1.5 A
R9
R9
R1- R11 R11 B
R3
R3
R4
R4
R4
2
A
R11 R11 B
R2
R2
2.5 A
B
-

Table 10 Wind speed = 27m/s
5.5 Height
Altitude/Distance Category (AD)
AD7 AD1 AD2 AD3 AD4 AD5 AD6
R7 R4
R4
R4
R5
R5
R5
R7 R4
R4
R4
R5
R5
R5
R7
R7
R8
R9
R9
R1R2
R3
R3
R3
R4
R4
R9
R1- R11 R11 R2
R2
R2
R2
R11 R11 R1
R1
-

AD7
R6
R6
R11
R4
-

Racking Bands for Flat roofs
Table 11 Wind speed = 25m/s
5.5 Height
Altitude/Distance Category (AD)
β Side
AD1 AD2 AD3 AD4 AD5 AD6
1
A
R3
R3
R3
R4
R4
R5
B
R3
R3
R3
R4
R4
R5
1.5 A
R6
R6
R7
R7
R8
R9
B
R2
R2
R2
R3
R3
R3
2
A
R8
R9
R9
R1- R11 R11
B
R1
R1
R2
R2
R2
R2
2.5 A
R9
R1- R11 R11 B
R1
R1
R1
R1
3
A
R11 R11 B
R1
R1
3.5 A
R11 B
R1
4
A
B
-

Table 12 Wind speed = 23m/s
5.5 Height
Altitude/Distance Category (AD)
AD7 AD1 AD2 AD3 AD4 AD5 AD6
R5 R3
R3
R3
R4
R4
R5
R5 R3
R3
R3
R4
R4
R5
R9 R6
R6
R7
R7
R8
R9
R4 R2
R2
R2
R3
R3
R3
R8
R9
R9
R1- R11 R11
R1
R1
R2
R2
R2
R2
R9
R1- R11 R11 R1
R1
R1
R1
R11 R11 R1
R1
R11 R1
-

AD7
R5
R5
R9
R4
-

1.E.15 Percentage openings in racking walls stage 6
a. Assess the Effective External Racking Wall Area, AEX, of the ground floor for each wall as Length,
B or Width, A x Height from ground level to first floor level .:
AEX = A x H and B x H
b. Assess the Total Opening Area, AO , of the ground floor for each of the walls ( sum of lengths
times widths of all openings)
AO = Sum (( W1 x H1) + (W2 x H2) + ….(WN x HN) )
c. Assess the Allowable Percentage Wall Openings in each wall as percentage Total Opening Area /
Effective External Racking Wall Area for each external face of the building :
%Op = AO /AEX %
subject to the following:
• Where two framed openings are separated by less than 300mm and the heights of both
openings are greater than half the panel height, the area of opening should be taken as the
rectangle that encloses both openings.
• Where there are limited areas of alternative cladding panels such as timber cladding above
doors or windows (not exceeding 0.5 m2 these areas should be should be added to the areas
of openings.
• Where an opening is less than 300mm from the corner of a building and the depth of opening
is greater than half the panel height, and then the length of that part of the wall, up to and
including the opening, should be disregarded when determining the total length of wall.

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structure SBSG annex 1.F 2007

Effective External Racking Wall Area, AEX = L x H
Total Opening Area ,
AO = (W1 x H1) + (W2 x H1) + (W3 x H3)
Percentage Wall Opening,
%Op = ( AO / AEX ) x 100

H2

H

H1

H2
A3

A2

A1

H1

If P1 <300mm and H1 > H/2 ,then L becomes ( L – P1 )
If P2 < 300mm then ( A1 + A2) = (W1 +P2 + W2 ) x H1
If the area above an opening is timber cladding
then
A2 = W2 x (H1 + H2 )
and A3 = W3 x (H3 + H4)

P1

W1

P2

W2

P3

W3

P4

L = Length of wall

1.E.16 Masonry Cladding Arrangement stage 7
Assess the Masonry Cladding arrangement Type from the Table below
Masonry cladding arrangement type
Type 1
For masonry walls with
buttresses or returns not
less than 550mm length
and not more than 9m
centre to centre.

Type 2
For masonry walls with
buttresses or returns at one
end of wall not less than
550mm length with the other
end without buttresses or
returns less than 550mm
length and wall length not
more than 4.5m

Type 3
For masonry walls without
buttresses or returns or with
buttresses or returns of less than
550mm length.

1.E.17 Panel Sheathing and Nailing stage 8
a. The Wall Sheathing in combination with the nailing of the sheathing to the wall studs provides the
resistance of the wall to the racking ( wind ) force in the plane of that panel as shown in the
diagram in clause 1.E.10 and combinations of sheathing and nailing can be read from the relevant
charts below using the following information derived above
• Racking Band , R , from clause 1.E.14
• Percentage Openings from clause 1.E.15
• Masonry Wall Type from clause 1.E.16
a. Select the appropriate chart below based on the Wall Type and number of storeys
• Chart 1 provides wall sheathing for Wall Type 1 for 1 and 2 Storey buildings.
• Chart 2 provides wall sheathing for Wall Type 2 at 1 and 2 Storey buildings.
• Chart 3 provides wall sheathing for Wall Type 3 for 1 and 2 Storey buildings.
b. Read off the allowable walling configurations for the Racking Bands and Percentage Wall
Openings for each wall
• Double sheathed with 100mm nail centres
• Double sheathed with 150mm nail centres

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structure SBSG annex 1.F 2007

•
•
c.
d.

Single sheathed with 100mm nail centres
Single sheathed with 150mm nail centres
Select the most appropriate Walling Configurations Option
If the required percentage openings/racking bands are outwith the charts
• either reconsider the parameters particularly the Percentage Wall Openings;
• or consider introducing an internal racking wall ( refer to clause 1.E.18);
• or specialist advice should be sought from chartered engineers with the appropriate skills
and experience.

Charts 1-3 Wall details and allowable percentage of openings for given racking banding
70

A llo
w ab
le
per
cen
tag
e
ope
ning
in
pan
el
%.

Perim eter nail spacing

D ouble sheathed w ith 100m m nail centres

60

D ouble sheathed w ith 150m m nail centres

50

S ingle sheathed w ith 100m m nail centres

40
S ingle sheathed w ith 150m m nail centres

30

20

10

0
R1

R2

R3

R4

R5

R6

R7

R8

R9

R 10

R 11

R acking band

Chart 1 Wall Type 1 at 1 & 2 Storey: Wall details and allowable percentage of openings for
given racking banding

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structure SBSG annex 1.F 2007

70

Perimeter nail spacing

Double sheathed with 100mm nail centres

Allowable percentage opening in panel %.

60

Double sheathed with 150mm nail centres

50

Single sheathed with 100mm nail centres

40
Single sheathed with 150mm nail centres

30

20

10

0
R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

Racking band

Chart 2 Wall Type 2 at 1 & 2 Storey: Wall details and allowable percentage of openings for
given racking banding

70

Perimeter nail spacing

Double sheathed with 100mm nail centres

Allowable percentage opening in panel %.

60

Double sheathed with 150mm nail centres

50

Single sheathed with 100mm nail centres

40
Single sheathed with 150mm nail centres

30

20

10

0
R1

R2

R3

R4

R5

R6

R7

R8

R9

R10

R11

Racking band

Chart 3

Wall Type 3 at 1 & 2 Storey: Wall details and allowable percentage of openings
for given racking banding

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structure SBSG annex 1.F 2007

1.E.18 Use of internal walls for additional racking resistance stage 9
Internal walls can be used to provide additional racking resistance provided the following apply to
such walls
a. satisfactory fixity to the foundations , floor or roof diaphragms as appropriate
b. no segments of wall being used is less than 600 mm in length
c. the assessed internal racking length is the shortest length of all storeys in that direction ( eg for a
2 storey building, if level one has 2 internal racking walls of say C1 and C3 and level two has only
C2, then C is the smaller of (C1+C3) and C2, for that building).
Key
A is the smaller dimension of the building plan
B is the larger dimension of the building plan
C is the sum of the lengths of the internal racking
resisting walls (C = C1 + C2 + C3 + ….),
β
can be considered as B/(A+0.5×C) but not less than 1.0
in any case. It is recommended that this value is always
rounded up when calculated (i.e. if A = 3, B = 5 and C =
1.2 then β= 5/(3+0.5×1.2) = 1.38 thus adopt β= 1.5 but if
A = 4, B = 5 and C = 2.5 then β= 5/(4+0.5×2.5) = 0.92
thus adopt β=1.0)

C1
RA

A

C2
B

C3

RB

Plan where there are internal racking
walls

Internal racking walls parallel to the length of the building (i.e. B) should be ignored in the calculation
of β. However they can be used to enhance racking resistance in that direction to allow for an
increased percentage of openings as follows:
The Effective internal racking wall area, AIN, should be split equally between each of the external
racking wall areas, AEX, which are parallel to that internal wall allowing the allowable percentage of
opening calculated from clause 1.E.15 may be increased using the following equation:
AOP = (AEX + (AIN / 2)) × %Op
Where:
Area of allowable opening
AOP
AEX
Effective external racking wall area
AIN
Effective internal racking wall area
%Op Allowable percentage of openings per storey from charts 1-3 .

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structure SBSG annex 1.F 2007

1.E.19 Horizontal loads stage 10
The Horizontal ( wind ) loads are derived from the wind speed map and can be read from the table
below using the following information derived from above
• Overall Building height, H from clause 1.E.10
• Distance to the coast , Site Altitude and Wind Speed from clause 1.E. 12
Table of Horizontal Loads
Building
height
<5.5m

<10m

Building
height
<5.5m

<10m

Wind
speed
(m/s)
23
25
27
30
23
25
27
30
Wind
speed
(m/s)
23
25
27
30
23
25
27
30

Site altitude (a)
a < 50m
50m< a < 100m
Distance to the coast(km)
<100 >100 <10 <100 >100 <10
<100 >100
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H2
H1
H1
H1
H1
H2
H2
H1
H2
H2
H2
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H1
H2
H1
H1
H1
H1
H2
H1
H1
H2
H2
H2
H2
H2
H3
H2
H2
H3
H3
H2
0m

<10
H1
H1
H1
H2
H1
H1
H2
H2

Site altitude (a)
200m< a < 300m
Distance to the coast(km)
>100
<10
<100
>100
H1
H2
H2
H1
H1
H2
H2
H1
H1
H3
H3
H2
H2
H4
H4
H3
H1
H2
H2
H2
H2
H3
H3
H2
H2
H4
H3
H3
H3
H5
H5
H4

150m< a < 200m
<10
H1
H2
H2
H3
H2
H3
H3
H4

<100
H1
H2
H2
H3
H2
H3
H3
H4

100m< a < 150m
<10 <100 >100
H1
H1
H1
H1
H1
H1
H2
H2
H1
H3
H2
H2
H1
H1
H1
H2
H2
H1
H2
H2
H2
H4
H3
H3

300m< a < 400m
<10
H2
H3
H4
H5
H3
H3
H5
H6

<100
H2
H3
H3
H4
H3
H3
H4
H6

>100
H1
H2
H3
H3
H2
H3
H4
H5

1.E.20 Vertical Loads stage 11
The Vertical loads are derived from the snow zone map in clause 1.E.12 using the following
information derived from above
• Roof and Floor Spans and the Number of Storeys from clause 1.E.10
• Snow Zone and Site Altitude from clause 1.E.12
a.

The Imposed Loads (Snow ) in kN/m2 is read from the table below

Zone

Altitudes below 100m

A
B

0.75
1.00

Imposed roof loads ( kN/m2 )
Altitudes between 100m Altitudes between 200m
and 200 m
and 260 m
1.00
Refer to BS 6399: Part 3
1.50
1.5

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b.

structure SBSG annex 1.F 2007

Read the Vertical ( Snow) Load Category (V1-V18) from the table below

Table of vertical loads at heads of panels
Imposed loads
Roof or
floor span
(m)

1
2
3
4
5
6
7
7.5

1.0 kN/m2

0.75 kN/m2
Roof or
floor

Roof +
1 storey

V1
V4
V6
V8
V10
V10
V11
V11

V3
V7
V10
V12
V13
V14
V16
V17

Roof or
floor
V1
V4
V6
V8
V10
V11
V11
V13

Roof +
1 storey
V3
V7
V10
V12
V14
V15
V16
V17

1.5 kN/m2
Roof or
floor
V2
V5
V7
V9
V11
V11
V12
V13

Roof +
1 storey
V3
V7
V11
V13
V14
V15
V17
V18

1.E.21 Wall Stud Sizing stage 12
The wall studs carry the horizontal and vertical loads imposed on the timber frame panels and the
sizes of studs can be selected using the tables below using the following information derived from
above
• Horizontal (Wind) Load Category (H1-5) from clause 1.E.19
• Vertical(Snow) Load Category (V1-V22) from clause 1.E.20
The most appropriate wall stud sizes , spacing and timber grade for the wall panels should be
selected from the tables below
Note that timber of strength class C16 is generally used for wall studs
Tables of Minimum wall stud sizes in softwood for all snow zones
Table 1 Horizontal load category H1
Timber of strength class grade C16
Vertical load Timber Size
Spacing
category
mm x mm
(mm)
V1-V11
38 x 89
400
V1-V7
600
V1-V20
38x 114
400
V1-V14
600
V1-V22
38 x 140
400
V1-V19
600

Timber of strength class grade C24
Vertical
load Timber Size
Spacing (mm)
category
mm x mm
V1-V16
38 x 89
400
V1-V10
600
V1-V22
38x 114
400
V1-V17
600
V1-V22
38 x 140
400
V1-V19
600

Table 2 Horizontal load category H2
Timber of strength class grade C16
Vertical load Timber Size
Spacing
category
mm x mm
(mm)
V1-V11
38 x 89
400
V1-V5
600
V1-V19
38x 114
400
V1-V12
600
V1-V22
38 x 140
400
V1-V18
600

Timber of strength class grade C24
Vertical
load Timber Size
Spacing (mm)
category
mm x mm
V1-V15
38 x 89
400
V1-V9
600
V1-V22
38x 114
400
V1-V16
600
V1-V22
38 x 140
400
V1-V19
600

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structure SBSG annex 1.F 2007

Table 3 Horizontal load category H3
Timber of strength class grade C16
Vertical load Timber Size
Spacing
category
mm x mm
(mm)
V1-V9
38 x 89
400
V1-V3
600
V1-V17
38x 114
400
V1-V12
600
V1-V21
38 x 140
400
V1-V18
600

Timber of strength class grade C24
Vertical
load Timber Size
Spacing (mm)
category
mm x mm
V1-V13
38 x 89
400
V1-V7
600
V1-V22
38x 114
400
V1-V14
600
V1-V22
38 x 140
400
V1-V19
600

Table 4 Horizontal load category H4
Timber of strength class grade C16
Vertical load Timber Size
Spacing
category
mm x mm
(mm)
V1-V8
38 x 89
400
V1
600
V1-V16
38x 114
400
V1-V10
600
V1-V21
38 x 140
400
V1-V16
600

Timber of strength class grade C24
Vertical
load Timber Size
Spacing (mm)
category
mm x mm
V1-V12
38 x 89
400
V1-V6
600
V1-V22
38x 114
400
V1-V13
600
V1-V22
38 x 140
400
V1-V19
600

Table 5 Horizontal load category H5
Timber of strength class grade C16
Vertical load Timber Size
Spacing
category
mm x mm
(mm)
V1-V7
38 x 89
400
None
600
V1-V16
38x 114
400
V1-V19
600
V1-V21
38 x 140
400
V1-V15
600

Timber of strength class grade C24
Vertical
load Timber Size
Spacing (mm)
category
mm x mm
V1-V12
38 x 89
400
V1-V5
600
V1-V21
38x 114
400
V1-V12
600
V1-V22
38 x 140
400
V1-V19
600

1.E.22 Cripple Stud Sizing stage 13
Cripple studs are connected to studs either side
of an opening within a panel to provide support
to a lintel above the openings as shown opposite.
The sizes and numbers of cripple studs can be
cripple
selected using the table below using the following
studs
information derived from above
• Lintel Span from clause 1.E.10
• Vertical Load Category (V1-V22) from
clause 1.E.20
a. Select the most appropriate cripple stud
reproduced by permission of TRADA
sizes, numbers of sections and timber grade
required for the lintel spans from the tables
below
b. The number of cripple studs required from the table is the number of studs in addition to the wall
studs on each side of the opening
c. All cripple studs should be of the same strength class and size
d. Timber of strength class C16 is generally used for posts/cripple studs
e. Where more than 3 sections are required to make up a cripple stud specialist advice should be
obtained.

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structure SBSG annex 1.F 2007

Minimum Cripple stud sizes and numbers in softwood
Table 1 Timber of Strength class Grade C16
Vertical load
Lintel span (mm)
category
1240
1800
38x89
38x114 38x140 38x89
38x114 38x140
Stud size
V1
1
1
1
1
1
1
V2
1
1
1
1
1
1
V3
1
1
1
1
1
1
V4
1
1
1
1
1
1
V5
1
1
1
2
1
1
V6
2
1
1
2
1
1
V7
2
1
1
2
1
1
V8
2
1
1
2
1
1
V9
2
1
1
2
1
1
V10
2
1
1
2
1
1
2
1
1
3
1
V11
2
V12
2
1
1
3
2
1
V13
2
1
1
3
2
1
V14
3
2
1
-2
2
V15
3
2
1
-2
2
V16
3
2
1
-2
2
V17
3
2
1
-3
2
V18
3
2
1
-3
2
Table 2 Timber of Strength class Grade C24
Lintel span (mm)
Vertical load
1240
1800
category
38x89
38x114 38x140 38x89
38x114 38x140
Stud size
V1
1
1
1
1
1
1
V2
1
1
`1
1
1
1
V3
1
1
1
1
1
1
V4
1
1
1
1
1
1
V5
1
1
1
1
1
1
V6
1
1
1
2
1
1
V7
2
1
1
2
1
1
V8
2
1
1
2
1
1
V9
2
1
1
2
1
1
V10
2
1
1
2
1
1
1
1
3
1
1
V11
2
1
1
3
2
1
V12
2
1
1
3
2
1
V13
2
2
1
-2
2
V14
3
2
1
-2
V15
3
2
1
1
3
2
V16
3
2
3
2
1
-3
2
V17
3
2
1
-3
2
V18

38x89
1
1
2
2
2
2
2
2
2
3

2475
38x114
1
1
1
1
1
1
1
1
2
2

38x140
1
1
1
1
1
1
1
1
1
1

3

2

1

-------

2
2
3
3
3
3
3

2
2
2
2
2
2
2

3
--

2475
38x114
1
1
1
1
1
1
1
1
1
1
2
2

-------

2
3
3
3
3
3

38x89
1
1
1
2
2
2
2
2
2
3

38x140
1
1
1
1
1
1
1
1
1
1
1
2
2

2
2
2
2
2

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structure SBSG annex 1.F 2007

1.E.23 Lintel Sizing
Lintels provide support to openings and are supported by cripple studs at either end as shown on the
diagram to clause 1.E.22 The sizes and numbers of sections for lintels can be selected using the
table below using the following information derived from above
• Lintel Span from clause 1.E.10
• Vertical Load Category (V1-V22) from clause 1.E.20
a. Select the most appropriate lintel sizes, numbers of sections and timber grade required for the
lintel spans from the table below
• The lintel span is the clear distance between support points of the cripple studs
• Timber of strength class C24 is generally used for lintels
• All lintels should be of the same strength class and size.
• 2x38x190 means 2 No lintels 38 mm wide by 190 mm deep are required to satisfy the
loading condition
• Where more than 3 sections are required to make up a lintel, or steel inserts (e.g. flitch
beams) are required then specialist advice should be obtained.

V1
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11
V12
V13
V14
V15
V16
V17
V18

2
2

2
2

2

2
2

2

2
2
2
2
2

2
2
2
2

3
3
3
3

3
3

2
2
2
2
2
3
3
3
3

44x240

44x2200

44x190

44x140

38x190

2
2

2

2475

38x140

44x240

44x2200

44x190

44x140

38x190

38x140

44x240

44x2200

44x190

44x140

38x190

Vert
load

38x140

Minimum lintel sizes and numbers in softwood
Table 1 Timber of Strength class Grade C16
Lintel span (mm)
1240
1800
Lintel sections and numbers

3
3
3
-----

3
-----

---

---

structure SBSG annex 1.F 2007

V1
V2
V3
V4
V5
V6
V7
V8
V9
V10
V11
V12
V13
V14
V15
V16
V17
V18

2
2

2
2
2
2
2
2

2
2

2
2

2
2

3
2
2

3
3

3
3

44x240

2
2

2
2
3
3

44x2200

2

2
2

3

44x190

2
2

2
2
2

38x190

2

2
2

2
2

2475

38x140

44x240

44x2200

44x190

44x140

38x190

38x140

44x240

44x2200

44x190

44x140

38x190

Vertical
load
category

38x140

Minimum lintel sizes and numbers in softwood
Table 2 Timber of Strength class Grade C24
Lintel span (mm)
1240
1800
Lintel sections and numbers

44x140

domestic

2
3
3
--

-3
----

--

----

domestic

structure SBSG annex 1.F 2007

1.E.24 Example

m

7.5
7.6
5.5
2
7.5
Duo
2.4

D2 = 1.4m

C 1 = 3.3m

C 2 = 2.5m
C3 = 2.5m
D3 = 1.9m

m
m
m
No
m

B = 7.6m

D1 = 2.7m

m/s

15
150
A
23.5

A = 7.5m

km
m

B = 7.6m

C 5 = 2.4m

D5 = 4.1m

C6 = 2.4m
D4 = 4.1m

7.5m

A = 7.5m

5.5m

2.4m

C4 = 2.4m

2.4m

7.5m

Site Data
Distance from sea
Altitude ,a
Snow zone
Windspeed
Building Data
Width, A
Length, B
Height to Eaves
Storeys
Building Height, H
Roof Shape
Panel Height, Hp

Racking
Wall Type: 1
Number of storeys: 2
From Table to clause 1.E.13, Altitude-Distance Category = AD3
For Ground Floor:
Internal racking wall, parallel to building width, C = C1 + C2 + C3 = 8.3m
Internal racking wall, parallel to building length, D = D1 + D2 + D3 = 6.0m
For First Floor:
Internal racking wall, parallel to building width, C = C4 + C5 + C6 = 7.2m
Internal racking wall, parallel to building length, D = D4 + D5 + = 8.2m
Adopt lesser values giving :
C = 7.2m.
D = 6.0m
Length/width ratio β = B/ (A + 0.5 ×C) = 7.6/ (7.5 + 3.6) = 0.68. < 1.0 . Therefore adopt β = 1.0
From Table 4 for β = 1.0 ,AD3 category and wind speed of 23 m/s , Racking bands are :
For Side A = R4 and for Side B = R5)
From the above parameters the initial wall options are as shown in the table below (before allowing
for the effect of internal racking walls)
Side
Racking Wall Options
Allowable %
Band
opening/ level per
side
Side A R4
From Chart 1 to clause 1.E.17:
1. Single sheathed with 100mm nail centres
19
2. Single sheathed with 150mm nail centres
14
Side B R5
3. Single sheathed with 100mm nail centres
15
4. Single sheathed with 150mm nail centres
10
In accordance with clause 1.E.18 ,% openings in the external walls may be increased:

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structure SBSG annex 1.F 2007

Width Walls:
Effective area of external racking wall, AEX
= 7.5m × 2.4m = 18m2
Effective area of internal racking walls, AIN
= 7.2m × 2.4m = 17.28m2
Area of allowable opening per level,
AOP = (AEX + (AIN / 2)) × %Op
For example consider Side A, Option 1: single sheathed with 100mm nail centres:
AOP = (18+ (17.28/2)) × 19%
AOP = 5.1m2
Therefore
%Op = (5.1 / 18) × 100 = 28%
Length Walls:
= 7.6m x 2.4m = 18.24m2
Effective area of external racking wall, AEX
Effective area of internal racking walls, AIN
= 6m x 2.4m = 14.4m2
Area of allowable opening,
AOP = (AEX + (AIN / 2)) × %Op
For example consider Side B, Option 5: single sheathed with 100mm nail centres:
AOP = (18.24m2 + (14.4m2/2)) × 15%
AOP = 3.82m2
Therefore
%Op = (3.82m2 / 18.24 m2) × 100 = 21%
The table can therefore be revised as follows allowing for internal racking walls effect
Side
Rackin Wall Options
Approximate
g Band
allowable
%
opening
per
level per side
Side A
R4
1. Single sheathed with 100mm nail centres
2. Single sheathed with 150mm nail centres
28
21
Side B
R5
3. Single sheathed with 100mm nail centres
21
4. Single sheathed with 150mm nail centres
14
Wall studs
From table to 1.E.19 , horizontal load category is H1
From table 1.E.20 , imposed load =1.00 kN/m2 leading to vertical load category = V17
From table 1 to 1.E.21 select 38x 140, grade wall stud at 600mm spacing
Cripple studs
For load V17 and 1200 mm opening ,table 1 to 1.E.22 gives 1 no 38 x 140 cripple studs grade C16
each side of opening
Lintels
For load V17 and 1200 mm opening ,table 2 ,to 1.E.23 gives 3 no 44x220, grade C24 lintels

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structure SBSG annex 1.F 2007

1.E.25 Overall Stability
To ensure there is an adequate factor of safety against overturning or sliding of a building with timber
frame walls when subjected to the various loads and load combinations all parts of the walls require to
be proportioned and connected as set out in this Annex including connections to floors, roofs and
under building. It is also to be noted that the stability of the building during construction is to be
considered.
1.E.26 Maximum allowable length and height of wall
This Annex does not deal with walls longer than 12 m, measured from centre to centre of buttressing
walls, providing restraint, or of walls exceeding 10 m in height.
Construction materials and workmanship
1.E.27 General
The construction materials and methods are restricted to those materials, timber strength classes,
specifications, and dimensions which are most commonly used in Scotland for simple platform timber
frame buildings as shown on the diagram below.
Typical timber frame wall panel
Stud depth plus sheathing

pa

ne

th
ng
e
l
l

Panel height
Sheathing

Plastic tape or similar locates stud
positions for wall tie fixing
Breather membrane (may be
site or factory fixed )
Bottom rail
Studs
Dwang (if required may be site
or factory fixed)
reproduced by permission of TRADA

1.E.28 Wall ties
Wall ties should comply with BS EN 845-1 and be material references 1 or 3 in BS EN 845 Table
A1 austenitic stainless steel.
The type of tie should be selected by reference to DD 140-2: type 5(timber frame) or type 6(timber
frame high movement) relevant to the performance levels given in DD140-2.
Ties should permit vertical flexibility to permit vertical downward of timber frame in relation to the
masonry cladding on the basis of differential movement of 6 mm/ storey height.
Reference should also be made to 1.D.16 with respect to the masonry cladding and in particular
to notes 1 and 2.

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structure SBSG annex 1.F 2007

1.E.29 Masonry Cladding
A typical masonry clad timber frame wall is illustrated below
Cavity barrier or batten
for fixing window
Vertical dpc
Dwang to
window opening

Cripple stud to support
lintel over ceiling
Internal wall lining
Thermal insulation
Studs
Sheathing
Breather membrane
Flexible wall tie, nailed to studs
Bottom rail
Sole plate
dpc

Vented cavity
Masonry cladding
Finished ground level

Floor dpm lapped over wall
and dressed under dpc

Inner leaf of
brickwork or
concrete block

reproduced by permission of TRADA

1.E.30 Brick and block construction
Brick and block used as masonry cladding should be in accordance with Annex 1.D in particular
1.D17-21 and should be in accordance with BS 5628 parts 1-3 , at least 100 mm thick with a minimum
density of 7.36 kN/m3
1.E.31 Mortar
Mortar used as masonry cladding should be in accordance with Annex 1.D in particular 1.D.22
1.E.32 Lintels for masonry cladding
Proprietary steel or concrete lintels suitable for use with masonry cladding to timber frame
construction should have independent certification and be in accordance with the manufacturer’s
recommendations.
Under no circumstances should the weight of masonry walls be transferred to the timber frame.
1.E.33 Timber members
Timber studs, bottom and top rails ,sole plates head binders , cripple studs, lintels etc should be dry
graded and marked timber of species and grade combinations to satisfy strength classes C16 or C24
to BS 5268: Part 2: 2002.
The cross sectional dimensions given in this Annex are :
a. CLS or ALS sizes in accordance with BS EN 336:2003 ,Table NA .5 to tolerance class 2; or
b. equivalent timbers with dimensions in accordance with BS EN 336:2003 ,Table NA .4 to tolerance
class 2 ( but should not have lesser dimensions to those in a above )
c. Although 38 mm widths are provided in the tables above for studs, cripple studs and lintels 44 mm
width timbers are commonly used to provide an increased width to which plasterboard can be
fixed.
1.E.34 Wall Sheathing
Plywood used as sheathing to timber frame should be 9.5 mm minimum thickness of species and
grade as defined in BS 5268: Part 2: 2002 ,Bonding Class 2 or 3 to BS EN 314-2
Oriented Strand Board used as sheathing to timber frame should be 9.0 mm minimum thickness,

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structure SBSG annex 1.F 2007

Type OSB 3: Load bearing boards for use in humid conditions to BS EN 300 Oriented Strand Board
Plasterboard used as wall linings and contributing to the structure of timber frame walls should be
12.5 mm minimum thickness for stud centres not more than 600 mm to BS 1230-1 .
1.E.35 Fasteners
All structural fasteners should be corrosion resistant and checked for compatibility with preservative,
treatments used and any other metalwork with which they are in contact.
Nails should be manufactured from mild or stainless steel and be of round head or “D” head
configuration to the diameter and length stated.
1.E.36 Fabrication
Timber frame walls should be fabricated, assembled and erected in accordance with section 6 of BS
5268-6.1.
Timber members in wall panels should be not less than 38 mm × 72 mm rectangular section with
linings fixed to the narrower face, with ends cut square.
Masonry cladding should be constructed on to the building foundation and tied back to the timber
frame structure with a nominal cavity width of 50 mm between the inside face of the masonry cladding
and the outer face of the timber frame wall.
1.E.37 Composite Action
To ensure that timber frame walls act in a composite manner they must be constructed in accordance
with 1.E.36 and 1.E.38 ensuring that sheathings and linings are nailed to all perimeter and
intermediate timber members as on the diagram below.
Sheathing edges should be backed by, and nailed to timber framing at all edges and where sheathing
is nailed to studs; the nails should be not less than 7 mm from the edge of the board or the face of the
stud.
For plasterboard linings nails should be not less than 10 mm from formed board edges and not less
than 13 mm from ends of the board at a spacing not exceeding 150 mm.
Internal walls which are lined with plasterboard should be connected to the wall studs at the same
perimeter nail spacing as the external sheathing material.
Perimeter Nailing Diagram

1.E. 38 Wall Panel Connections
Where wall panels are combined to form the lengths of wall given it is essential that the following
conditions are met to ensure that the coupled panels should be able to resist overturning forces:

domestic

structure SBSG annex 1.F 2007

1. Tops and bottoms of individual wall panels are linked by a head binder and sole plate respectively
that are continuous across panel joints including at junctions of the same dimensions as the top
and bottom rails by means of 3.75 mm nails of length 75 mm nails at 600 mm centres.
2. The sole plates should be secured to either the concrete floor slab or the header joists in the case
of a timber ground floor or the header joists of the intermediate floor
3. The header plates should be secured to the header joists of the intermediate floor or the roof
trusses.
4. The faces of end studs of contiguous panels are fixed such that any vertical shear is transferred.
In the absence of more specific information, this should be by 3.35mm nails of length 75mm at
300mm centres.
5. All edges including to openings for windows, doors etc other than the bases of door openings and
small openings should be supported by members having a thickness not less than the thickness of
the studs.
6. The wall diaphragm details derived by following this guidance assume that the walls under
consideration are adequately fixed to ensure resistance to sliding and overturning.
7. Where a secondary board is fixed on the same side of a wall as the primary sheathing then the
nail lengths given in the table should be increased to take account of the additional thickness
A means should be provided of transferring horizontal forces in the plane of the panel above and
below openings. Where no such provision is made, the wall lengths on either side of the opening
should be designed as separate parts.
1.E.39 Nailing and fixing schedule
Item
Proposed
Foundations
Sole plate to underbuilding
4.7 kN shear resistance fixings at 600 mm centres
Holding Down Straps
Stainless steel strap 30 mm x 2.5 mm attached to stud by 6
no 65x3.35 ring shank nails at 2400 centres L shaped end of
strap under masonry cladding
Wall Panels
Top rail of Panels to head binders
Tops of individual wall panel members linked by member
continuous across panel joints secured with 90x4.00mm
galvanised wire nails, 2 nails between stud centres
Sole plate to ring beam/ joist
90x4.00mm galvanised wire nails, 2 nails between stud
centres.
Bottom rail to sole plate
90x4.00mm galvanised wire nails, 2 nails between stud
centres..
Wall Panel stud to wall panel stud
90x4.00mm galvanised wire nails, at 600mm centres each
side staggered.
Header plate to Intermediate floor
90x4.00mm Galvanised wire nails at 300mm centres
maximum. Nails skewed externally through rimboard into
headbinder, and internally, skewed through the headbinder
into the joists.
Perimeter Studs to sheathing
3.00mm x 50 mm wire nails 100 or 150 mm c/c as calculated
Intermediate studs to sheathing
3.00mm x 50 mm wire nails 2x perimeter spacing as
calculated
Studs to plasterboard
2.65 mm x 40mm Smooth shanked galvanised flat round
headed nails min , max 150 mm c/c
Top and bottom rails to studs
2 no 90 mm nails end fixed

domestic

structure SBSG annex 1.F 2007

1. Multi-cripple studs should be secured to each other with 3.1mm dia. ×
64mm long galvanised ringshank nails at 400mm centres staggered mid
distance between edge and centreline with no nail closer than 60mm to
end of studs.

2. Lintels should be secured to each other with 3.1mm dia.
× 75mm long galvanised screws at 300mm centres
staggered mid distance between edge and centreline with
no screw closer than 60mm to end of lintel.
300 mm

3. Holding down straps should be provided at 2.4m centres, at every opening and at the end studs
of a wall attached to the studs in a manner to provide at least 3.5kN of resistance. This is
normally achieved by using 6 no 65x35mm ring shank nails or equivalent attaching the strap to
the stud and placing the L-shaped end of the strap under the masonry cladding creating the
holding down resistance.
Loadings on walls
1.E.40 Maximum span of floors
The maximum span for any floor supported by a wall
should be 6.0 m, where the span is measured centre to
centre of bearing as opposite.

Floor span max 6m
Packer

Floor
deck

Head binder
Masonry

reproduced by permission of TRADA

Floor member bearing on wall
1.E.41 Other loading conditions
a. Vertical loading on walls such as timber floors and flat roofs designed in accordance with Annex
1.F, timber roof trusses.
b. The combined dead and imposed load should not exceed 70kN/m at base of wall
c. Timber frame walls should commence above ground level and therefore should not be subject to
lateral loads other than from wind .

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structure SBSG annex 1.F 2007

1.E.42 End restraint
The wind load is resisted primarily by transfer directly to the foundations at the base of the wall and by
the racking resistance of the timber frame supporting walls, the load having been transferred via the
floor and ceiling diaphragms.
The ends of every wall should be securely tied throughout their full height to walls which are providing
racking resistance.
Normally supporting walls are the external walls perpendicular to the wall subject to wind load and are
designed as racking walls.
The use of internal walls to provide additional racking resistance is outwith the scope of this Annex
and specialist advice should be obtained.
Openings, notching and drilling
1.E.43 General
The number, size and position of openings must not impair the stability of a wall or the lateral
support afforded to a supported wall. Construction over openings must be adequately supported.
1.E.44 Framing of openings
a. Lintels supporting masonry cladding over openings should
be structurally independent of the timber frame ensuring no
loads from the masonry cladding are carried by the timber
frame.
b. Loads over openings in timber frame wall panels are
carried independently by timber lintels. Lintels should be
supported by cripple studs as shown opposite and the lintel
loads carried down on to the floor below.

cripple
studs

reproduced by permission of TRADA

1.E.45 Dimensional criteria for openings and recesses
The dimensional criteria are given in the diagram to 1.F.15
No openings should be provided in walls below ground floor except for small holes for services
and ventilation etc. which should be limited to a maximum area of 0.1 m2 at not less than 2 m
centres .
1.E.46 Small unframed openings
The size and position of small openings should be restricted as follows:
a) not exceed 250mm in diameter or in length of side; and
b) clear distance between openings should be not less than the greatest dimension of the openings;
and
c) clear distance between the edge of sheathing and the edge of any opening should be not less
than the greatest dimension of the opening; and
d) not more than one such opening should occur in any one 600mm width of sheathing or lining.
Smaller unframed openings may occur to a greater extent, but their aggregate opening area should
not exceed the total area of opening given in item a). The rules governing the position of openings
given in items b), c) and d) should also apply.

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structure SBSG annex 1.F 2007

1.E.47 Notching & drilling
Holes should be within the limits set out
opposite and as follows :
• holes should be drilled at the neutral axis
• holes should be not less than 300mm
apart
Notching is not permitted in wall studs, cripple
studs and lintels.

D

0.25H
0.4H
holes on centreline
only. Hole diameter
not greater than 0.25D
and not closer than 300mm

H

0.25H

0.4H

max 0.25 D

1.E.48 Lateral support by roofs and floors
The wall panels in each storey of a building should extend to the full height of that storey, and be
connected the floors and roofs to provide adequate diaphragm action and transfer lateral forces from
the walls to the racking walls ,be of normal construction and:
a. intermediate floors require the floor deck or sub-deck fixed directly to the top faces of the joists,
or the floor braced by some other means
b. pitched roofs require the plasterboard ceiling to be fixed directly under the roof, together with the
roof bracing recommended in BS5268-3
c. be secured to the supported wall by connections specified in clause 1.E.39
1.E.49 Differential movement
Allowance should be made for differential movement
particularly vertical movement between timber frame
walls and masonry cladding. The allowances
opposite are based upon:
a. conventional platform frame construction
b. concrete ground floor
c. 200 mm deep intermediate floor joists
d. installed timber moisture content of 20 % drying
to 10%
If timber ground floors are used then add 8 mm to
all allowances shown opposite
For a timber frame extension connected to an
existing traditional masonry wall the roof to the
extension should be supported on a timber bearer
connected to the existing wall to minimise the
differential movement in the supports to the
extension roof .

allowance at eaves
and verge

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structure SBSG annex 1.F 2007

Annex
1.F
Timber floor and roof members
1.F.0 Introduction
1.F.1 The use of this Annex
1.F.2
Common timber species/grade combinations
1.F.3 Notches and holes
1.F.4 Strutting to Joists
Loadings
1.F.5 Dead loads
1.F.6 Imposed roof loads including snow
Spans, sizes and spacings for timber members
1.F.7 General
1.F.8 Floor joist tables
1.F.9 Joists for flat roofs tables for maintenance or repair purposes
1.F.10 Joists for flat roofs tables not limited to maintenance or repair
purposes
1.F.11 Raised tie roofs
1.F.12 Collared roofs
1.F.13 Connections for raised tie and collared roofs

contents

domestic

structure SBSG annex 1.F 2007

annex

1.F

Sizes of certain timber floors and roof members

1.F.0 Introduction
This Section applies only to domestic buildings with the exception of flats and maisonettes of not
more than three storeys.
Where trussed rafters are used reference should be made to BS 5268: Part 3: 1998 for design and
bracing recommendations.
1.F.1 The use of this Annex
This Annex should be used in conjunction with Annex 1.B
The guidance given in this Annex assumes that a. the dead and imposed loads to be sustained by the floor, ceiling, or roof of which the member
forms part, do not exceed the values given in the notes to the appropriate diagrams and tables;
b. the species and grade of timber for the strength class to which the table to 1.F.2 relates is
either:
• as in 1.F.2 for more common species, or
• as in the more comprehensive tables of BS 5268: Part 2: 2002; and
c. that floorboarding complying with BS 1297: 1987 or moisture resistant wood chipboard type P5
complying with BS EN 312 is used.
d. the strength classes, species, grades and species combinations are as defined in BS 5268: Part
2: 2002.
e. the cross sectional dimensions are :
• CLS or ALS sizes in accordance with BS EN 336:2003 ,Table NA .5, tolerance class 2;
• equivalent timbers to dimensions in accordance with BS EN 336:2003 ,Table NA .4 ,tolerance
class 2 but not lesser dimensions to those above
The tables do not apply where these dimensions have been reduced, in the case of tables to 1.F.8 by
planing and in the case of tables to 1.F.9 by planing or regularising. For timber of North American
origin the tables only apply as indicated to surfaced sizes unless the timber has been resawn to BS
EN 336 requirements.
Bearing areas and workmanship should comply with the relevant requirements of BS 5268: Part 2:
2002. Refer also to clauses 1.D.34-36 or clauses 1.E.48 respectively for masonry and timber frame
walls.

domestic

structure SBSG annex 1.F 2007

1.F.2

Common species/grade combinations satisfying the strength classes to which
1.F.8-12 relates.
Grades to satisfy strength
Species
Origin
Grading rule
C16
C24
All species listed in
BS EN 519
machine graded to C16 machine graded to C24
this table
Imported Redwood
BS 4978
GS
SS
or Whitewood
Douglas Fir
UK
BS 4978
SS
Larch
SS
British Pine
British Spruce
Douglas Fir-Larch
Hem-Fir
Spruce-Pine-Fir
Sitka spruce
Douglas Fir-Larch

Canada

BS 4978

Canada

NLGA

Canada

MSR

USA

BS 4978

USA

NGRDL

Hem-Fir
Spruce-Pine-Fir
Sitka spruce
Douglas Fir-Larch
Hem-Fir
Spruce-Pine-Fir
Douglas Fir-Larch
Hem-Fir
Southern Pine
Spruce-Pine-Fir
Western
Whitewoods
Douglas Fir-Larch

SS
SS
GS

SS

GS
GS
SS
Joist & plank No 1 & 2
Structural L.F. No 1 & 2
Joist & plank No 1 & 2
Structural L.F. No 1 & 2
Joist & plank No 1 & 2
Structural L.F. No 1 & 2
Joist & plank select
Structural L.F
1450f-1.3E
1450f-1.3E
1450f-1.3E
GS
GS
GS
GS
SS

SS
SS
Joist & plank select
Structural L.F select
Joist & plank select
Structural L.F select
Joist & plank select
Structural L.F select
1800f-1.6E
1800f-1.6E
1800f-1.6E
SS
SS
SS
SS
-

Joist & plank No 1 & 2
Joist & plank select
Structural L.F. No 1 & 2 Structural L.F select
Hem-Fir
Joist & plank No 1 & 2
Joist & plank select
Structural L.F. No 1 & 2 Structural L.F select
Spruce-Pine-Fir
Joist & plank No 1 & 2
Joist & plank select
Structural L.F. No 1 & 2 Structural L.F select
Western
Joist & plank select
Whitewoods
Structural L.F
Southern Pine
Joist & plank No 3
Joist & plank select
Stud grade
Douglas Fir-Larch
USA
MSR
1450f-1.3E
1800f-1.6E
Hem-Fir
1450f-1.3E
1800f-1.6E
Southern Pine
1450f-1.3E
1800f-1.6E
Spruce-Pine-Fir
1450f-1.3E
1800f-1.6E
1 The species/grade combinations given in this Table are for particular use with the other Tables in
this Annex and for the cross section sizes given in those Tables.
2 The grading rules for American and Canadian Lumber are those approved by the American Lumber
Standards Board of Review and the Canadian Lumber Standards Accreditation Board respectively
(see BS 5268: Part 2: 2002).

domestic

structure SBSG annex 1.F 2007

1.F.3 Notches and holes
Notches and holes in simply
supported floor and flat roof
joists should be within the limits
Max D/8
set out below and as follows :
holes should be drilled at the
neutral axis
notches and holes should be
not less than 100mm apart
horizontally; notches may be
at the top or bottom of a joist
but not coinciding. notches
should not be cut in rafters,
purlins or binders unless
approved by the building
designer

0.25L min
0.07L min

0.4L min
0.07L min

1.F.4 Strutting to Joists
Floor joists spanning more than 2.5m should be strutted by one or more rows of solid as shown
in the following table.
Solid timber strutting should be at least 38mm thick extending at least 3/4 depth of joist.
Joist span

Number of rows

m

of strutting

Less than 2.5

none

2.5 to 4.5

1

more than 4.5

2

Loading
1.F.5 Dead floor and roof loads
Construction

Position

at mid span
at one third span

Dead load
( kN/m2 )

Floors
Floor boards , 13 mm plasterboard
0.22
Floor boards , 19 mm plasterboard
0.27
Floor boards , ash deadening, lath &plaster
1.18
Flat roofs
3 layer felt , 16 mm decking , 100mm mineral wool , vapour layer , 13 mm 0.32
plasterboard
13 mm chippings ,50 mm rigid insulation , vapour layer, 19 mm decking , 13 0.6
mm plasterboard
13 mm chippings , 19 mm mastic asphalt , decking , 100 mm mineral wool 0.90
,vapour layer, 13 mm plasterboard
Note that the above is based on 600 mm joist spacing and excludes the weight of the joists and any
partitioning

domestic

1.F.6

structure SBSG annex 1.F 2007

Imposed roof loads including snow

The map opposite indicates the zones within
Scotland where the snow loading on flat roofs is not
expected to exceed the values set out in the table
below of 0.75, 1.00 or 1.5 kN/m2, depending on
geographical location and altitude.
This guidance applies only to pitched and freestanding flat roofed structures with the roof on one
level only within the limits set out on the tables to
clauses 1.F.8-12, provided that there are no other
buildings within 1.5m of its perimeter but does not
apply to trussed rafter roofs.
For all other circumstances, reference should be
made to BS 6399: Part 3: 1988: Code of Practice for
Imposed Roof Loads.

Zone
Altitudes below 100m
A

0.75

B

1.00

Zone
A
B

Inverness

Imposed roof loads ( kN/m2 )
Altitudes
between Altitudes
between
100m and 200 m
200m and 260 m
1.00
Refer to BS 6399: Part
3
1.50
1.5

domestic

structure SBSG annex 1.F 2007

Spans, sizes and spacings for timber members
1.F.7 General
The following Table refers to further tables and diagrams with accompanying notes that give
spans, sizes and spacings for certain timber floor and flat roof and pitched roof members .In clauses
1.F.8-12 all spans, except those for floorboards, are measured as the clear dimensions between
supports, and all spacings are the dimensions between longitudinal centres of members.
Key to Tables relating to timber members
Timber
Construction
members
Floors
Flat roofs
access for maintenance only
full access allowed
Raised tie roofs
Collared roofs

Table numbers for strength classes
C16

C24

joists

1.F.8

1.F.8

joists
joists
All
All

1.F.9
1.F.10
1.F.11
1.F.12

1.F.9
1.F.10
1.F.11
1.F.12

1.F.8 Floor joists
The tables below give sizes, spacings and spans for floor
joists which will support the dead loads given in the
Tables and an imposed load not exceeding 1.5kN/m2.
Partition loads have not been allowed for
Softwood tongued and grooved floorboards if supported at
a joist spacing of up to 450mm shall be at least 16mm
thick; and if supported at wider spacings up to 600mm
should be 19mm thick.
Wood chipboard, type P5, if supported at a joist spacing of
up to 450mm shall be at least 18mm thick and if supported
at wider spacing up to 600mm shall be 22mm thick.
Floor joists selected from these tables may be used for
intermediate floors in timber frame construction but will
require header joists around the perimeter.
T & G Chipboard flooring should be fixed by 3.35 mm 65
mm angular ring shank nails at 200 mm c/c perimeter and
300 mm intermediate and recommended to be glued by
PVA adhesive between boards and joists to boards to
prevent creaking ( per BS 8103-3)

domestic

structure SBSG annex 1.F 2007

Permissible clear spans of joists supporting floors with no partitions.
Timber of strength class C16
Dead load
Size of joist
kN/m2
Not more than 0.25
More than 0.25 but not
More than 0.50 but not
more than 0.50
more than 1.25
Spacing of joists
mm
400
450
600
400
450
600
400
450
600
mm× mm
Maximum clear span of joist
m
BS EN 336 sizes
1.037
1.301
1.423
1.214
1.556
1.717
1.303
1.692
1.828
38 × 97
1.448
1.791
1.947
1.755
2.215
2.368
1.925
2.385
2.482
38 × 122
1.872
2.290
2.453
2.331
2.707
2.853
2.510
2.868
2.983
38 × 147
2.267
2.649
2.808
2.690
3.098
3.281
2.873
3.306
3.442
38 × 170
2.609
3.010
3.189
3.056
3.518
3.724
3.263
3.752
3.939
38 × 195
2.920
3.367
3.567
3.418
3.932
4.161
3.648
4.193
4.434
38 × 220
0.783
0.993
1.091
0.891
1.154
1.272
0.942
1.233
1.324
47 × 72
1.228
1.527
1.665
1.460
1.818
1.920
1.583
1.914
2.024
47 × 97
1.696
2.081
2.255
2.087
2.450
2.548
2.302
2.561
2.663
47 × 122
2.174
2.570
2.723
2.609
2.945
3.062
2.786
3.078
3.200
47 × 147
2.552
2.942
3.116
2.987
3.398
3.533
3.188
3.551
3.691
47 × 170
2.900
3.341
3.538
3.391
3.889
4.042
3.619
4.063
4.221
47 × 195
3.244
3.735
3.954
3.791
4.354
4.549
4.044
4.572
4.723
47 × 220
1.919
2.197
2.319
63 × 97
1.533
1.839
1.934
1.822
2.079
2.191
2.566
2.821
2.931
63 × 122
2.088
2.429
2.527
2.454
2.700
2.807
3.084
3.388
3.518
63 × 147
2.577
2.920
3.037
2.950
3.244
3.370
3.905
4.055
63 × 170
2.950
3.370
3.504
3.404
3.741
3.886
3.558
4.465
4.633
63 × 195
3.350
3.850
4.009
3.896
4.278
4.442
4.070
4.923
5.061
63 × 220
3.745
4.301
4.512
4.365
4.770
4.905
4.580
2.327
2.575
2.677
2.601
2.859
2.970
2.718
2.985
3.100
75 × 122
2.807
3.094
3.216
3.125
3.432
3.564
3.265
3.582
3.719
75 × 147
3.212
3.569
3.709
3.605
3.957
4.107
3.765
4.128
4.283
75 × 170
3.646
4.084
4.242
4.125
4.523
4.683
4.306
4.700
4.830
75 × 195
4.074
4.595
4.740
4.641
4.971
5.109
4.793
5.128
5.268
75 × 220
CLS/ALS sizes
0.910
1.149
1.259
1.052
1.356
1.499
1.121
1.463
1.617
38 × 89
1.752
2.149
2.330
2.167
2.587
2.719
2.398
2.733
2.843
38 × 140
2.471
2.852
3.022
2.895
3.334
3.530
3.092
3.557
3.721
38 × 184
3.110
3.590
3.800
3.640
4.180
4.430
3.890
4.460
4.710
38 × 235

domestic

structure SBSG annex 1.F 2007

Permissible clear spans of joists supporting floors with no partitions.
Timber of strength class C24
Dead load
Size of joist
kN/m2
Not more than 0.25
More than 0.25 but not More than 0.50 but
more than 0.50
not more than 1.25
Spacing of joists
mm
400
450
600
400
450
600
400
450
600
mm× mm
Maximum clear span of joist
m
BS EN 336 sizes
38 × 97
1.936
1.829
1.586
1.838
1.739
1.514 1.635 1.551 1.358
38 × 122
2.582
2.482
2.200
2.469
2.369
2.076 2.180 2.073 1.826
38 × 147
3.103
2.984
2.709
2.969
2.854
2.588 2.667 2.561 2.305
38 × 170
3.580
3.444
3.128
3.426
3.294
2.989 3.079 2.958 2.678
38 × 195
4.096
3.941
3.581
3.921
3.771
3.423 3.526 3.388 3.068
38 × 220
4.609
4.436
4.034
4.413 4.246
3.856
3.971 3.816 3.458
1.103 1.223 1.159 1.010
1.273
1.347
1.144
1.324
1.404
47 × 72
1.678 1.795 1.705 1.499
1.920
2.026
1.763
2.025
2.141
47 × 97
2.290 2.382 2.268 2.006
2.549
2.651
2.421
2.664
2.770
47 × 122
2.783 2.865 2.754 2.496
3.064
3.185
2.910
3.201
3.327
47 × 147
3.212 3.307 3.179 2.883
3.535
3.674
3.359
3.693
3.836
47 × 170
3.678 3.786 3.640 3.302
4.045
4.202
3.845
4.224
4.387
47 × 195
4.141 4.262 4.099 3.720
4.552
4.707
4.328
4.725
4.860
47 × 220
1.925 2.032 1.934 1.709
2.192
2.308
2.030
2.321
2.432
63 × 97
2.553 2.628 2.527 2.273
2.808
2.918
2.669
2.933
3.046
63 × 122
3.069 3.158 3.038 2.759
3.372
3.503
3.207
3.521
3.665
63 × 147
3.541 3.643 3.505 3.185
3.888
4.037
3.699
4.058
4.211
63 × 170
4.052 4.168 4.011 3.646
4.445
4.614
4.231
4.637
4.770
63 × 195
4.560 4.678 4.514 4.106
4.908
5.046
4.731
5.064
5.204
63 × 220
2.705 2.784 2.678 2.433
2.972
3.086
2.827
3.102
3.220
75 × 122
3.250 3.344 3.218 2.925
3.567
3.703
3.394
3.721
3.862
75 × 147
3.748 3.855 3.711 3.376
4.110
4.265
3.913
4.286
4.446
75 × 170
4.287 4.408 4.245 3.864
4.686
4.816
4.474
4.833
4.966
75 × 195
4.778 4.878 4.743 4.350
5.113
5.253
4.932
5.272
5.415
75 × 220
CLS/ALS sizes
1.341 1.464 1.388 1.201
1.544
1.633
1.399
1.617
1.713
38 × 89
2.466 2.541 2.440 2.170
2.719
2.829
2.581
2.844
2.957
38 × 140
3.232 3.329 3.199 2.897
3.561
3.703
3.382
3.723
3.869
38 × 184
4.120 4.240 4.080 3.700
4.540
4.700
4.310
4.710
4.850
38 × 235

domestic

structure SBSG annex 1.F 2007

1.F.9 Joists for flat roofs with access only for the purposes of maintenance or repair
The tables below give sizes, spacings and spans for flat
roof joists designed for access only for maintenance
which will support the dead loads given in the Tables and
an imposed load not exceeding 0.75 kN/m2 or an
imposed concentrated load of 0.9KN.

o
an
Sp

Roof
joist

fr

sts
joi
f
oo

support

Roof joist
spacing

The tables are for
a slope of up to
10 from the
horizontal

Joists for flat roofs with access only for the purposes of maintenance or repair
Timber of strength class C16.
Dead load kN/m2
Size of joist
mm× mm
Not more than 0.5
More than 0.5 but not
More than 0.75 but not
more than 0.75
more than 1.00
Spacing of joists (mm)
400
450
600
400
450
600
400
450
600
Maximum clear span of joist
m
BS EN 336 sizes
1.738 1.719 1.666 1.666 1.642 1.578 1.605 1.578 1.507
38 × 97
2.368 2.336 2.250 2.250 2.212 2.113 2.155 2.113 2.005
38 × 122
3.020 2.974 2.851 2.851 2.797 2.659 2.717 2.659 2.511
38 × 147
3.631 3.571 3.368 3.412 3.342 3.166 3.239 3.166 2.980
38 × 170
4.303 4.226 3.855 4.025 3.939 3.629 3.810 3.719 3.446
38 × 195
4.943 4.762 4.340 4.641 4.491 4.087 4.383 4.274 3.881
38 × 220
1.272 1.260 1.229 1.229 1.214 1.175 1.192 1.175 1.130
47 × 72
1.919 1.896 1.835 1.835 1.808 1.735 1.765 1.735 1.654
47 × 97
2.602 2.565 2.468 2.468 2.425 2.313 2.360 2.313 2.192
47 × 122
3.304 3.252 3.115 3.115 3.055 2.900 2.964 2.900 2.736
47 × 147
3.960 3.892 3.612 3.716 3.639 3.402 3.525 3.444 3.232
47 × 170
4.677 4.530 4.132 4.372 4.277 3.893 4.136 4.037 3.700
47 × 195
5.282 5.093 4.649 4.991 4.808 4.383 4.747 4.577 4.166
47 × 220
2.190 2.162 2.088 2.088 2.055 1.968 2.005 1.968 1.873
63 × 97
2.948 2.905 2.790 2.790 2.740 2.609 2.664 2.609 2.469
63 × 122
3.722 3.662 3.444 3.503 3.434 3.246 3.330 3.256 3.069
63 × 147
4.439 4.345 3.969 4.161 4.074 3.744 3.945 3.853 3.561
63 × 170
5.141 4.961 4.537 4.864 4.689 4.282 4.612 4.468 4.074
63 × 195
5.771 5.572 5.101 5.464 5.270 4.816 5.212 5.024 4.585
63 × 220
75 × 122
3.168 3.121 2.995 2.995 2.940 2.797 2.857 2.797 2.645
75 × 147
3.984 3.919 3.640 3.747 3.672 3.435 3.561 3.481 3.268
75 × 170
4.736 4.583 4.194 4.439 4.334 3.959 4.208 4.110 3.768
75 × 195
5.415 5.229 4.791 5.129 4.949 4.526 4.894 4.719 4.310
75 × 220
6.000 5.869 5.383 5.758 5.558 5.088 5.497 5.303 4.847
CLS/ALS sizes
38 × 89
1.543 1.528 1.484 1.484 1.464 1.410 1.433 1.410 1.350
38 × 140
2.836 2.794 2.682 2.682 2.633 2.505 2.559 2.505 2.369
38 × 184
4.007 3.937 3.641 3.755 3.676 3.427 3.559 3.476 3.254
38 × 235
5.271 5.078 4.630 4.975 4.790 4.360 4.726 4.556 4.142

domestic

structure SBSG annex 1.F 2007

Joists for flat roofs with access only for the purposes of maintenance or repair
Timber of strength class C24.
Dead load
Size of joist
kN/m2
mm× mm
Not more than 0.5
More than 0.5 but not
More than 0.75 but not
more
more than 1.00
than 0.75
Spacing of joists
mm
400
450
600
400
450
600
400
450
600
Maximum clear span of joist
m
BS EN 336 sizes
1.837 1.816 1.759 1.759 1.733 1.664 1.693 1.664 1.588
38 × 97
2.496 2.462 2.370 2.370 2.329 2.223 2.267 2.223 2.108
38 × 122
3.177 3.128 2.997 2.997 2.939 2.792 2.853 2.792 2.635
38 × 147
3.814 3.750 3.503 3.580 3.507 3.298 3.398 3.320 3.123
38 × 170
4.512 4.399 4.009 4.218 4.127 3.775 3.991 3.895 3.586
38 × 195
5.134 4.947 4.512 4.847 4.668 4.251 4.586 4.441 4.039
38 × 220
1.347 1.334 1.300 1.300 1.284 1.241 1.259 1.241 1.192
47 × 72
2.025 2.001 1.935 1.935 1.905 1.826 1.860 1.826 1.740
47 × 97
2.739 2.700 2.596 2.596 2.549 2.430 2.480 2.430 2.301
47 × 122
3.472 3.416 3.256 3.269 3.205 3.041 3.110 3.041 2.868
47 × 147
4.153 4.081 3.755 3.894 3.813 3.538 3.693 3.607 3.363
47 × 170
4.879 4.704 4.294 4.575 4.441 4.048 4.327 4.223 3.849
47 × 195
5.482 5.287 4.831 5.182 4.995 4.556 4.938 4.756 4.333
47 × 220
2.307 2.277 2.198 2.198 2.162 2.069 2.108 2.069 1.968
63 × 97
3.098 3.052 2.929 2.929 2.876 2.736 2.795 2.736 2.588
63 × 122
3.903 3.838 3.578 3.670 3.597 3.375 3.487 3.409 3.212
63 × 147
4.645 4.509 4.123 4.353 4.261 3.891 4.125 4.029 3.702
63 × 170
5.332 5.147 4.712 5.047 4.868 4.449 4.816 4.640 4.235
63 × 195
5.983 5.779 5.296 5.668 5.470 5.003 5.409 5.216 4.764
63 × 220
3.325 3.274 3.141 3.141 3.082 2.931 2.994 2.931 2.770
75 × 122
4.172 4.103 3.781 3.921 3.842 3.569 3.725 3.641 3.397
75 × 147
4.924 4.754 4.354 4.638 4.498 4.113 4.396 4.289 3.916
75 × 170
5.612 5.422 4.973 5.319 5.135 4.700 5.078 4.899 4.477
75 × 195
6.000 6.000 5.585 5.969 5.765 5.283 5.703 5.503 5.035
75 × 220
CLS/ALS sizes
1.633 1.615 1.568 1.568 1.546 1.488 1.513 1.488 1.424
38 × 89
2.985 2.940 2.820 2.820 2.768 2.632 2.689 2.632 2.487
38 × 140
4.205 4.131 3.787 3.937 3.854 3.566 3.730 3.642 3.387
38 × 184
5.473 5.275 4.813 5.169 4.979 4.535 4.921 4.737 4.310
38 × 235

domestic

structure SBSG annex 1.F 2007

1.F.10 Joists for flat roofs access not limited to maintenance or repair purposes
The tables below give sizes, spacings and spans for flat
roof joists designed for access not limited to maintenance or
ts
ois
j
repair purposes which will support the dead loads given in
f
oo
the Tables and an imposed load not exceeding 1.5 kN/m2
fr
o
an
or an imposed concentrated load of 1.8 kN.
Sp
Roof
joist

support

Roof joist
spacing

The tables are for
a slope of up to
10 from the
horizontal

Joists for flat roofs access not limited to maintenance or repair purposes
Timber of strength class C16.
Dead load kN/m2
Not more than 0.5
More than 0.5 but not
More than 0.75 but not
more than 0.75
more than 1.00
Spacing of joists (mm)
400
450
600
400
450
600
400
450
600
Size of joist
Maximum clear span of joist
mm× mm
m
BS EN 336 sizes
1.090
1.130
1.145
1.130
1.164
1.176
1.176
1.202
1.211
38 × 97
1.573
1.647
1.675
1.647
1.712
1.736
1.736
1.785
1.798
38 × 122
2.088
2.177
2.207
2.177
2.246
2.272
2.272
2.327
2.347
38 × 147
2.533
2.641
2.681
2.641
2.736
2.771
2.771
2.848
2.876
38 × 170
3.017
3.156
3.210
3.156
3.282
3.329
3.293
3.432
3.470
38 × 195
3.430
3.680
3.747
3.564
3.838
3.897
4.030 3.710
4.078
38 × 220
0.802
0.825
0.833
0.825
0.844
0.850
0.850
0.864
0.869
47 × 72
1.210
1.362
1.375
1.362
1.363
1.404
1.404
1.428
1.436
47 × 97
1.809
1.871
1.894
1.871
1.925
1.944
1.944
1.986
2.000
47 × 122
2.311
2.403
2.438
2.403
2.484
2.513
2.513
2.578
2.601
47 × 147
2.784
2.907
2.953
2.907
3.015
3.056
3.056
3.144
3.176
47 × 170
3.282
3.463
3.524
3.401
3.605
3.659
3.539
3.777
3.820
47 × 195
3.697
4.027
4.102
3.831
4.204
4.271
3.986
4.383
4.477
47 × 220
1.625
1.655
1.666
63 × 97
1.526
1.572
1.589
1.572
1.611
1.625
2.236
2.287
2.306
63 × 122
2.070
2.146
2.174
2.146
2.212
2.236
2.874
2.953
2.981
63 × 147
2.631
2.741
2.783
2.741
2.838
2.874
3.585
3.624
63 × 170
3.157
3.301
3.356
3.277
3.430
3.478
3.408
4.286
4.338
63 × 195
3.623
3.917
3.987
3.752
4.084
4.146
3.900
4.816
4.999
63 × 220
4.079
4.483
4.624
4.224
4.639
4.821
4.390
2.237
2.322
2.354
2.322
2.396
2.423
2.423
2.482
2.503
75 × 122
2.835
2.957
3.003
2.957
3.065
3.105
3.105
3.193
3.225
75 × 147
3.353
3.551
3.611
3.472
3.694
3.747
3.609
3.865
3.908
75 × 170
3.838
4.203
4.280
3.973
4.360
4.454
4.128
4.526
4.663
75 × 195
4.321
4.742
4.923
4.472
4.904
5.088
4.645
5.088
5.278
75 × 220
CLS/ALS sizes
38 × 89
1.038
1.032
1.012
1.012
1.003
0.977
0.988
0.977
0.946
38 × 140
2.190
2.173
2.123
2.123
2.101
2.038
2.065
2.038
1.942
38 × 184
3.206
3.173
3.082
3.082
3.040
2.929
2.976
2.929
2.803
38 × 235
4.449
4.360
3.960
4.242
4.175
3.804
4.072
3.996
3.647

domestic

structure SBSG annex 1.F 2007

Joists for flat roofs access not limited to maintenance or repair purposes
Timber of strength class C24.
Dead load
Size of joist
kN/m2
mm× mm
Not more than 0.5
More than 0.5 but not
More than 0.75 but not
more than 0.75
more than 1.00
Spacing of joists
mm
400
450
600
400
450
600
400
450
600
Maximum clear span of joist
m
BS EN 336 size
1.367 1.359 1.337 1.337 1.327 1.298 1.311 1.298 1.263
38 × 97
1.908 1.895 1.856 1.856 1.838 1.788 1.809 1.788 1.729
38 × 122
2.486 2.464 2.404 2.404 2.377 2.301 2.333 2.301 2.214
38 × 147
3.041 3.011 2.928 2.928 2.889 2.787 2.831 2.787 2.671
38 × 170
3.663 3.622 3.429 3.511 3.460 3.294 3.383 3.326 3.176
38 × 195
4.299 4.247 3.862 4.104 4.041 3.711 3.943 3.872 3.580
38 × 220
0.982 0.978 0.966 0.966 0.960 0.944 0.951 0.944 0.924
47 × 72
1.526 1.517 1.490 1.490 1.478 1.444 1.459 1.444 1.403
47 × 97
2.120 2.104 2.058 2.058 2.037 1.979 2.004 1.979 1.911
47 × 122
2.751 2.725 2.656 2.656 2.623 2.536 2.573 2.536 2.437
47 × 147
3.354 3.319 3.216 3.223 3.179 3.062 3.112 3.062 2.931
47 × 170
4.026 3.980 3.682 3.853 3.795 3.540 3.708 3.643 3.417
47 × 195
4.711 4.556 4.147 4.491 4.385 3.987 4.310 4.230 3.849
47 × 220
1.766 1.754 1.722 1.722 1.706 1.663 1.682 1.663 1.613
63 × 97
2.439 2.418 2.362 2.362 2.336 2.265 2.295 2.265 2.183
63 × 122
3.146 3.116 3.030 3.030 2.992 2.887 2.931 2.887 2.769
63 × 147
3.818 3.776 3.544 3.661 3.609 3.409 3.529 3.471 3.292
63 × 170
4.561 4.449 4.055 4.357 4.289 3.902 4.187 4.112 3.769
63 × 195
5.191 5.003 4.564 5.003 4.820 4.393 4.839 4.660 4.243
63 × 220
75 × 122
2.644 2.261 2.557 2.557 2.528 2.448 2.482 2.448 2.356
75 × 147
3.399 3.364 3.253 3.269 3.226 3.110 3.160 3.110 2.980
75 × 170
4.111 4.065 3.751 3.938 3.881 3.611 3.794 3.729 3.488
75 × 195
4.785 4.700 4.291 4.673 4.529 4.131 4.489 4.380 3.991
75 × 220
5.477 5.283 4.827 5.283 5.093 4.648 5.113 4.927 4.493
CLS/ALS sizes
38 × 89
1.203 1.197 1.180 1.180 1.171 1.148 1.158 1.148 1.119
38 × 140
2.321 2.302 2.248 2.248 2.223 2.155 2.185 2.155 2.077
38 × 184
3.387 3.351 3.238 3.253 3.208 3.088 3.139 3.088 2.953
38 × 235
4.686 4.535 4.122 4.464 4.362 3.961 4.282 4.202 3.822

domestic

structure SBSG annex 1.F 2007

1.F.11 Raised tie roof
The tables below give member sizes for raised tie roofs designed for access limited to maintenance
or repair purposes which will support dead load not exceeding 0.75 kN/m2 and an imposed load not
exceeding 1.5 kN/m2 for truss centres of 400 , 450 and 600 mm
Ridge
Sarking
Rafters

Tie Joist

30 - 55

h

Maximum span 5000 mm

Timber of strength class C16
Rafter Size
Tie Joist Size
mm×mm
mm×mm
47×220
47×220
47×195
47×195
47×195
47×195

h (max)
mm
575
450
325

Span (max)
mm
5,000
5,000
5,000

Timber of strength class C24( TR26)
Rafter Size
Tie Joist Size
mm×mm
mm×mm
47×170 or 38×195
47×170 or 38×195
38×195
38×195
38×195
38×195

h (max)
mm
575
450
325

Span (max)
mm
5,000
5,000
5,000

Roof bracing to comply with BS 5268: part 3
Masonry walls to comply with Annex 1.D and be cavity walls comprising 100 mm thick 3.5 N/mm2
blockwork inner leaf and 102 mm thick brickwork outer leaf
Connection details should be as in 1.F.13
Trusses to be tied down to walls in accordance with 1.E.39

domestic

structure SBSG annex 1.F 2007

1.F.12 Collared roof
The tables below give member sizes for collared roofs designed for access limited to maintenance or
repair purposes which will support dead load not exceeding 0.75 kN/m2 and an imposed load not
exceeding 1.5 kN/m2 for truss centres of 400, 450 and 600 mm and spans of 6.0m and 7.5 m.
Roof space is for ceilings for access only for an imposed load of 0.25 kN/m2 together with a
concentrated load of 0.9kN and does not include for water tanks.

Ridge
Sarking
Rafters

H

Collars

H/2

Hangers

Ceiling tie

Maximum span 7500 mm

Span not exceeding 7.5 m
Timber of strength class C16
Centres
Rafter Size
mm
mm×mm
400
47×147
450
47×195
600
47×220

Ceiling Tie
mm×mm
47×147
47×195
47×220

Collar Size
mm×mm
47×97
47×122
47×147

Hanger Size
mm×mm
47×97
47×122
47×147

Span not exceeding 7.5 m
Timber of strength class C24( TR26)
Centres
Rafter Size
mm
mm×mm
400
47×147
450
47×147
600
47×195

Ceiling Tie
mm×mm
47×147
47×147
47×195

Collar Size
mm×mm
47×97
47×122
47×147

Hanger Size
mm×mm
47×97
47×122
47×147

Roof bracing to comply with BS 5268: part 3
Masonry walls to comply with Annex 1.D and be cavity walls comprising 100 mm thick 3.5 N/mm2
blockwork inner leaf and 102 mm thick brickwork outer leaf
Connection details should be as in 1.F.12
Trusses to be tied down to walls in accordance with 1.E.39

domestic

structure SBSG annex 1.F 2007

1.F.13 Connection details for raised tied and collared roofs
Connections for raised and collared roofs should be as shown below
Ceiling tie to rafter connection

Double sided
toothed connector

Grade 4.6 bolt

a. Up to 450mm rafter centres: 38mm diameter double sided toothed connector and M10, grade 4.6
bolts should be used.
b. Up to 600mm rafter centres: 51mm diameter double sided toothed connector and M12, grade 4.6
bolts should be used.