Low cost

Low Cost Housing Techniques

General:
In these days of increasing cost of instruction of the dream of owning a
house particularly for low income and middle income family is becoming a difficult reality.
Hence it has become a necessity to adopt cost effective, innovative and environmental
friendly housing technology for the construction of houses and buildings for enabling the
common people to construct houses at affordable cost.
Low Cost Housing :
Cost Effective Housing is a relative concept and has more to do with
budgeting and it seeks to reduce the cost construction through better management,
appropriate use of local materials, skills and technology but without sacrificing the
performance and life of the structure.
A low cost house is designed and constructed as any other house with
regard to foundation, structure,strength etc.The reduction in cost is achieved through
effective utilization of locally available building materials and techniques that are
durable,economical,accepted by users and not requiring costly maintenance,
Economy is also achieved by postponing finishing and/implementing them in
phases.Further,it aims at increasing the efficiency of workers, minimizing wastage in
design and space and applying good management practices, so that shelter can be
provided at prices which people can afford.

Low cost technologies and their utilizations:

Building materials constitute about 70% of the total cost of construction.
Inadequate supply and increasing prices of basic building materials, like bricks, timber,
etc. adversely affect the construction of houses and slow down the housing activity in the
country. Reduction in cost and increase in supply of such materials can be achieved by
manufacturing basic material required for housing from the raw materials available
locally. Thus, there is wide scope for development and utilisation of low cost
technologies and also use locally available building materials. In this connection, use of
fly ash brick, sand lime brick, phosphate gypsum calcium silicate, etc, maybe used in
areas where they are available in abundance. Most of these have been tested and found
to be fit for use.

Avenues for reducing cost of construction - concept:
The following are the avenues exist for reducing building construction cost:
• Reduce plinth area by using thinner wall concept. Ex.15 cms thick solid concrete
block wall.
• Use locally available material in an innovative form like soil cement blocks in
place of burnt brick.
• Use energy efficiency materials, which consume less energy like concrete block
in place of burnt brick.
• Use environmentally friendly materials, which are substitute for conventional
building components like use R.C.C.Door and window frames in place of
wooden frames.
• Preplan every component of a house and rationalize the design procedure for
reducing the size of the component in the building.
• By planning each and every component of a house the wastage of materials due
to demolition of the unplanned component of the house can be avoided.
• Each component of the house shall be checked whether if it's necessary, if it is
not necessary, then that component should not be used.
• Cost reduction is possible by eliminating redundant components
Ex: avoid plastering the walls, eliminating the use of plinth slabs in the
foundation.
• Accept lower quality finishes like exposed brick work without plastering.
• Reducing standards - providing jelly work in place of windows, no plinth concrete

Cost reduction through adhoc methods :

Foundation :

Normally the foundation cost comes to about 10 to 15% of the total building and
usually foundation depth of 3 to 4 ft. is adopted for single or double storey building and
also the concrete bed of 6"(15 cms.) is used for the foundation which could be avoided.
It is recommended to adopt a foundation depth of 2 ft.(0.6m) for normal soil like
gravely soil, red soils etc., and use the uncoursed rubble masonry with the bond stones
and good packing.Similiarly, the foundation width is rationalized to 2 ft.(0.6m).To avoid
cracks formation in foundation the masonry shall be thoroughly packed with cement
mortar of 1:8 boulders and bond stones at regular intervals.
It is further suggested adopt arch foundation in ordinary soil for effecting reduction in
construction cost upto 40%.This kind of foundation will help in bridging the loose pockets
of soil which occurs along the foundation.
In the case black cotton and other soft soils it is recommend to use under ream pile
foundation which saves about 20 to 25% in cost over the conventional method of
construction.
Arch Foundations :



In an arch foundation, the walls are supported on brick or stone masonry arches
springing from a series of square cement concrete bases. This method helps cut down
on the use of materials such as cement, coarse rubble stone and sand etc. It is also a
labour intensive system and requires a high degree of supervision. Arch foundation is
best to use if the condition of the soil is good and the building is low rise

Plinth:
It is suggested to adopt 1 ft. height above ground level for the plinth and
may be constructed with a cement mortar of 1:6. The plinth slab of 4 to 6" which is
normally adopted can be avoided and in its place brick on edge can be used for reducing
the cost. By adopting this procedure the cost of plinth foundation can be reduced by
about 35 to 50%.It is necessary to take precaution of providing imprevious blanket like
concrete slabs or stone slabs all round the building for enabling to reduce erosion of soil
and thereby avoiding exposure of foundation surface and crack formation.

Walling:

Wall thickness of 6 to 9" is recommended for adoption in the construction
of walls all round the building and 41/2 " for inside walls. It is suggested to use burnt
bricks which are immersed in water for 24 hours and then shall be used for the walls

Rat - trap bond wall:

It is a cavity wall construction with added advantage of thermal comfort
and reduction in the quantity of bricks required for masonry work. By adopting this
method of bonding of brick masonry compared to traditional English or Flemish bond
masonry, it is possible to reduce in the material cost of bricks by 25% and about 10to
15% in the masonry cost. By adopting rat-trap bond method one can create aesthetically
pleasing wall surface and plastering can be avoided.
Strength is equal to standard 9” brick wall, but consumes 20% less bricks.
The air medium that is created by the bond helps maintaining a good thermal comfort
inside the building.As the construction is appealing to the eye from both internally &
externally, plastering is not necessary. The overall saving on cost of this wall compared
to the traditional 9” wall is about 26%.





















Concrete block walling:

In view of high energy consumption by burnt brick it is suggested to use
concrete block (block hollow and solid) which consumes about only 1/3 of the energy of
the burnt bricks in its production. By using concrete block masonry the wall thickness
can be reduced from 20 cms to 15 cms. Concrete block masonry saves mortar
consumption, speedy construction of wall resulting in higher output of labour, plastering
can be avoided thereby an overall saving of 10 to 25% can be achieved.

Soil cement block technology:

It is an alternative method of construction of walls using soil cement blocks in
place of burnt bricks masonry. It is an energy efficient method of construction where soil
mixed with 5% and above cement and pressed in hand operated machine and cured
well and then used in the masonry. This masonry doesn't require plastering on both
sides of the wall. The overall economy that could be achieved with the soil cement
technology is about 15 to 20% compared to conventional method of construction.

Doors and windows:
More cost savings can be made by avoiding building windows and doors. It is
estimated that installing windows can cost up to 10 times more than the installation of a
wall. Instead, grills for light and air movement can be created in the brickwork. This is
known as "jali" in Indian.
It is suggested not to use wood for doors and windows and in its place concrete
or steel section frames shall be used for achieving saving in cost up to 30 to
40%.Similiarly for shutters commercially available block boards, fibre or wooden
practical boards etc shall be used for reducing the cost by about 25%.By adopting brick
jelly work and precast components effective ventilation could be provided to the building
and also the construction cost could be saved upto 50% over the window components.

Lintels and Chajjas :

The traditional R.C.C. lintels, which are costly, can be replaced by brick
arches for small spans and save construction cost upto 30 to 40% over the traditional
method of construction. By adopting arches of different shapes a good architectural
pleasing appearance can be given to the external wall surfaces of the brick masonry.

Roofing:

Normally 5” (12.5 cms) thick R.C.C. slabs are used for roofing of
residential buildings. By adopting rationally designed insitu construction practices like
filler slab and precast elements the construction cost of roofing can be reduced by about
20 to 25%.

Filler slabs:

Filler slabs are normal RCC slabs where bottom half (tension) concrete
portions are replaced by filler materials such as bricks, tiles, cellular concrete blocks,
etc., These filler materials are so placed as not to compromise structural strength, result
in replacing unwanted and nonfunctional tension concrete, thus resulting in economy.
These are safe, sound and provide aesthetically pleasing pattern ceilings and also need
no plaster. Materials that can replace the useless concrete between the reinforcement
are called filler materials.

Characteristics of filler materials:
• Cheaper than concrete
• Easily available
• Degree of thermal expansion shall be close to concrete

Examples for filler materials:
• Mangalore tiles
• Bricks
• Plastic wastes
• Coconut shells


Advantages of filler slabs:
• Cost effective
• Insulating
• Low energy
• Reduces dead load






J ack arch roof/floor:

J ack arch roof/floor is easy to construct, save on cement and steel, are more
appropriate in hot climates. These can be constructed using compressed earth blocks
also as alternative to bricks for further economy.

Corbelled Brick Pyramid :
Some roofs have replaced tiles and slabs with bricks. A brick roof is an ancient
traditional Indian construction technique and it uses less energy in construction than a
conventional concrete roof.
A brick placed on top of another one, with an overhang of less than half the length of the
brick will not topple and is called a corbelled brick. A pyramid has a polygon shaped
base and the other faces are triangular with a common vertex. A corbelled pyramid is
developed by creating layers of corbelled bricks



Micro-Concrete Roofing Tiles :
Micro-concrete roofing (MCR) tiles are made from locally available raw materials, for
example, sand, fine gravel, and cement using small stone chips. These tiles produce a
high quality, low cost roof which is cheaper, cooler and quieter than corrugated iron
sheets or asbestos. Roofing with MCR tiles is similar to conventional Mangalore tiled
roofing construction. It needs under structures, such as rafters and purlins which can be
wooden, ferrocement or steel, to support the tiles.
Cement Stabilised Mud Block Masonry :
Cement stabilised mud block (CSMB) is made by compacting a mixture of soil and
cement in a block making machine. The machine is usually operated manually and
requires no fuel for production. CSMBs are used in masonry in a similar manner to solid
conventional brick work, but the mortar used is stabilised soil. The local soil needs to
have the following range of particle distribution for it to be an effective component in the
creation of CSMBs - gravel: 0-10%; sand: 40-70%; silt: 15-25%; and clay: 8-25%.
CSMB masonry is effective where other walling materials are expensive, or of poor
strength, in areas with medium to low rainfall
Ferrocement channel/shell unit :

They provide an economic solution to RCC slab by providing 30 to 40% cost
reduction on floor/roof unit over RCC slabs without compromising the strength. These
being precast, construction is speedy, economical due to avoidance of shuttering and
facilitates quality control.
Finishing Work:
The cost of finishing items like sanitary, electricity, painting etc., varies depending
upon the type and quality of products used in the building and its cost reduction is left to
the individual choice and liking.

The above list of suggestion for reducing construction cost is of general nature and
it varies depending upon the nature of the building to be constructed, budget of the
owner, geographical location where the house is to be constructed, availability of the
building material, good construction management practices etc. However it is necessary
that good planning and design methods shall be adopted by utilizing the services of an
experienced engineer or an architect for supervising the work, thereby achieving overall
cost effectiveness to the extent of 25% in actual practice.
Prefabrication Building Methodologies for Low Cost Housing :

Prefabrication is when something is built from parts that have been made in a
factory and that are put together quickly to make an entire object or building.
The promotion of prefabrication building methodologies for low cost housing by
highlighting the different prefabrication techniques, and the economical advantages
achieved by its adoption.

Introduction:
In a building the foundation, walls, doors and windows, floor and roof are the
most important components. These components can be analysed individually based on
the needs. This will improve the speed of construction and reduce the
Construction cost.


Foundations :
Various type of foundations normally adopted are:

(i) Open foundations.
(ii) Rib foundations.
(iii) Columns and footings.
(iv) RCC raft foundation.

Conventional methods using in-situ techniques are found to be economical and
more practical for low cost housing of slums which generally consists of low rise
structures. In seismic regions, special attention is required to make the foundations
continuous using horizontal reinforcement. Prefabrication is not recommended for
foundations in normal situations.

Walls :
In the construction of walls, rammed earth, normal bricks, soil cement
blocks, hollow clay blocks, dense concrete blocks, small, medium and room size panels
etc of different sizes are used. However, bricks continue to be the backbone of the
building industry. In actual construction, the number of the bricks or blocks that are
broken into different sizes to fit into position at site is very large. As a result of this, there
is wastage of material and the quality of construction also suffers.
Increasing the size of wall blocks will prove economical due to greater
speed and less mortar consumption, which can be achieved by producing low-density
bigger size wall blocks and advantages of industrial wastes like blast furnace slag and fly
ash can be made.
Several prefabrication techniques have been developed and executed
for walls but these medium and large panel techniques have not proved economical for
low rise buildings as compared to traditional brick work.

Floor and Roof :
Structural floors/roofs account for substantial cost of a building in normal
situation. Therefore, any savings achieved in floor/ roof considerably reduce the cost of
buildings. Traditional cast-in-situ concrete roof involve the use of temporary shuttering
which adds to the cost of construction and time.
` Use of standardised and optimised roofing components where shuttering
is avoided prove to be economical, fast and better in quality. Some of the prefabricated
roofing/flooring components found suitable in many low-cost housing projects are:
(i) Precast RC planks.
(ii) Precast hollow concrete panels.
(iii) Precast RB panels.
(iv) Precast RB curved panels.
(v) Precast concrete/ferrocement panels.
(vi) Precast RC channel units.


Limitations of prefabrications:

(1) As the precast elements have to behave monolithic on erections, extra reinforcement
may be necessary in some cases.
(2) Extra reinforcement is required to take care of handling and erection stresses.
(3) Temporary props may be required in some cases, before the in-situ concrete joints
achieve strength.
(4) The cracks may develop at the joints between the precast and in-situ concrete due to
shrinkage and temperature stresses. To overcome them, extra steel is required across
the joint.
(5) As there are chances of leakage/seepage through the joints between the precast
components, extra care is required to make them leak proof.

Criteria for selection of prefabrication in India:

In India, the technology adopted for housing components should be of the
order that, the production and erection technology be adjusted to suit the level of skills
and handling facilities available under metropolitan, urban and rural conditions. In other
words, the structural systems and components selected should ensure minimum
material utilization with maximum structural advantage. However, the component and
systems so designed are to be manufactured and erected by manual means in villages,
semi mechanical techniques in towns and more or less fully mechanical operations in
the metropolitan cities.
In urban areas, the concentration of construction activity does not justify
prefabrication. The answer is hybrid construction combining standardised mass-
manufactured roofing and other components (at site) with in-situ brick walls or other
masonary structures. A wide variety of roofing methods to suit these requirements have
been developed and used on mass scale in many housing projects such as funicular
shell, cored slabs, RCC channel units, precast cellular units, precast RC planks and
joists, prefab brick panels and joists, RCC joists and hollow concrete blocks, precast
RCC ‘Kular’ slab.

Techniques:

Precast RC Plank Roofing System
This system consist of precast RC planks supported over partially precast
joist. The completely finished slab can be used as intermediate floor for living also. The
total thickness of slab is 6 cm. The scheme is ideally suited for spans upto 4.2 m,
but can be used for large spans, by providing secondary beams. RC planks are made
with thickness partly varying between 3 cm and 6 cm. There are haunches in the plank
which are tapered. When the plank is put in between the joists, the space above 3 cm
thickness is filled with in-situ concrete to get tee-beam effect of the joists. A 3 cm wide
tapered concrete filling is also provided for strengthening the haunch portion during
handling and erection. The planks have 3 numbers 6 mm dia MS main reinforcement
and 6 mm dia @ 20 cm centre to centre cross bars. Concrete used is of grade M-15.
The planks are made in module width of 30 cm with maximum length of 150 cm and the
maximum weight of the dry panel is 50 kg
Precast joist is rectangular in shape, 15 cm wide and the precast
portion is 15 cm deep The above portion is casted while laying in-situ concrete over
planks. The stirrups remain projected out of the precast joist. Thus, the total depth of the
joist becomes 21 cm. The joist is designed as composite
Tee-beam with 6 cm thick flange comprising of 3 cm precast and 3 cm in-situ concrete
(Figure 3). This section of the joist can be adopted upto a span of 400 cm. For longer
spans, the depth of the joist should be more and lifting would require simple chain pully
block.
In residential buildings, balcony projections can be provided along the
partially precast joists, designed with an overhang carrying super imposed loads for
balcony as specified in IS : 875-1964, in addition to the self load and the load due to
balcony railings. The main reinforcement of the overhang provided at the top in the in-
situ concrete attains sufficient strength. The savings achieved in practical
implementations compared with conventional RCC slab is about 25%.

Prefabricated Brick Panel Roofing System:
The prefabricated brick panel roofing system consists of:

(a) Prefab Brick Panel
Brick panel is made of first class bricks reinforced with two MS bars of 6
mm dia and joints filled with either 1:3 cement sand mortar or M-15 concrete. Panels can
be made in any size but generally width is 53 cm and the length between 90 cm to
120 cm, depending upon the requirement. The gap between the two panels is about 2
cms and can be increased to 5 cms depending upon the need. A panel of 90 cm length
requires 16 bricks and a panel of 120 cm require 19 bricks

(b) Partially Precast Joist
It is a rectangular shaped joist 13 cm wide and 10 cm to 12.5 cm deep with
stirrups projecting out so that the overall depth of joist with in-situ concrete becomes 21
cm to 23.5 cm, it is designed as composite Tee-beam with 3.5 cm thick flange.

Structural design:
The prefab brick panel for roof as well as for floor of residential buildings
has two numbers 6 mm dia MS bars as reinforcement upto a span of 120 cms.
The partially precast RC joist, is designed as simply supported Tee-beam with 3.5 cm
thick flange. The reinforcement in joist is provided as per design requirements
depending upon the spacing and span of the joist.
An overall economy of 25% has been achieved in actual practice
compared to cast-in-situ RCC slab.

Precast Curved Brick Arch Panel Roofing:
This roofing is same as RB panel roofing except that the panels do not
have any reinforcement. A panel while casting is given a rise in the centre and thus an
arching action is created. An overall economy of 30% has been achieved in single
storeyed building and 20% in two or three storeyed buildings

Precast RC Channel Roofing:
Precast channels are trough shaped with the outer sides corrugated
and grooved at the ends to provide shear key action and to transfer moments between
adjacent units. Nominal width of units are 300 mm or 600 mm with overall depths of 130
mm to 200 mm .The lengths of the units are adjusted to suit the span. The flange
thickness is 6
The width of a panel is 300 mm and depth may vary from 100 mm to
150 mm as per the span, the length of the panel being adjusted to suit the span. The
outer sides are corrugated to provide transfer of shear between adjacent units. The
.kulars. are placed inverted so as to create a hollow during precasting. Extra
reinforcement is provided at top also to take care of handling stresses during lifting and
placement. There is saving of about 30% in cost of concrete and an overall saving
of about 23%.

Precast Concrete Panels Roofing :
The system comprise of precast panels 600 mm ×600 mm and only
30 mm thick. The reinforcement consists of 2 mm dia MS wire or equivalent welded
mesh. The panels are 30 mm to 35 mm. Where balcony is provided, the units are
projected out as cantilever by providing necessary reinforcement for cantilever moment.
A saving of 14% has been achieved in actual implementation in various projects.

Precast Hollow Slabs Roofing :
Precast hollow slabs are panels in which voids are created by earthen
.kulars. without decreasing the stiffness or strength. These hollow slabs are lighter than
solid slabs and thus save the cost of concrete, steel and the cost of walling and
foundations too due to less weight.
placed over fully precast RCC beams of 75 mm width and 125 mm to 150 mm depth
depending on the span. The ends of panels are tapered so as to form a V-groove when
placed over beams. This groove is filled with cement mortar. The beams are designed
as simple supported.
After placement of panels and filling of the V-grooves a screeding
concrete 25 mm thick with chicken mesh reinforcement is laid. This screeding concrete
act as floor finish and as earthquake strengthening measure. The panels can also be
casted in ferrocement by using cement mortar 1:2 and fine 6 mm down grit and chicken
mesh reinforcement in two layers. A saving of about 25% has been achieved in actual
practice over conventional system.

OTHER USES OF PREFABRICATION :
The use of prefabrication for other materials can be made like lintels, sun
shades, cupboard shelves, kitchen working slab and shelves, precast ferrocement tanks,
precast staircase steps, precast ferrocement drains

(a) Thin Precast RCC Lintel
Normally lintels are designed on the assumption that the load from a
triangular portion of the masonary above, acts on the lintel. Bending moment, will be
WL/8 where W is the load on the lintel and L is the span assumed for the design
purpose. By this method, a thickness of 15 cm is required. Thin precast RCC lintels are
designed taking into account the composite action of the lintel with the brick work.
Design chart prepared for thin precast RCC lintels in the brick walls of normal residential
building is applicable only when the load on the lintel is uniformly distributed. The brick
work over the lintel is done in a mortar not leaner than 1:6. The thickness of the lintel is
kept equal to the thickness of brick itself having a bearing of 230 mm on either supports.
Use of precast lintels speeds up the construction of walls besides eliminating shuttering
and centreing. Adoption of thin lintels results in upto 50% saving in materials and overall
cost of lintels.

(b) Doors and Windows
Innumerable types and sizes of doors and windows used in single and
similar buildings. This involves the use of additional skilled labour on site and off site and
also wastage of expensive materials like timber, glass etc. Economy can be achieved
by:

(i) standardising and optimising dimensions;
(ii) evolving restricted number of doors and window sizes; and
(iii) use of precast door and window frames.

for example:
• bed room, kitchen, entrance, living room, balcony doors 900 mm width and 2000
mm height; and
• windows of 400 mm, 800 mm, 1200 mm, width and of 400 mm, 800 mm, 1200
mm or 1600 mm heights.

CONCLUSION
Mass housing targets can be achieved by replacing the conventional
methods of planning and executing building operation based on special and individual
needs and accepting common denominator based on surveys, population needs and
rational use of materials and resources.
No single approach and solution is available which can satisfy the
community at large. However, what is ideal and desirable is to have a system which can
provide choice for people and also appropriate techniques to meet the situation. The
essence lies in the system approach in building methodology and not necessarily
particular construction type or design. Adoption of any alternative technology on large
scale needs a guaranteed market to function and this cannot be established unless the
product is effective and economical. Partial prefabrication is an approach towards the
above operation under controlled conditions. The methodology for low cost housing has
to be of intermediate type . less sophisticated involving less capital investment.