Thermal Insulation
Content
THERMAL INSULATION
Thermal insulation may be defined as a barrier to the natural flow of heat from an area of high temperature to an area of flow temperature. In building this flow is generally from interior to the exterior. Heat is a from of energy consisting of the ceaseless movement of tiny particles of matter called molecules; if these particles are moving fast they collide frequently with one another and the substance becomes hot. Temperature is the measure of hotness and should not be confused with heat. The transfer of heat can occur in three ways: Conduction – vibrating molecules come into contact with adjoining molecules and set them vibrating faster and hence they become hotter; this process is carried on throughout the substance without appreciable displacement of the particles. Convection – transmission of heat within a gas or fluid caused by the movement of particles which become less dense when heated and rise thus setting up a current or circulation. Radiation – heat is considered to be transmitted by radiation when it passes from one point to another without raising the temperature of the medium through which it travels. In a building all three methods of heat transfer can take place since the heat will be conducted through the fabric of the building and dissipated on the external surface by convection and/ or radiation. The traditional thick and solid building materials used in the past had a natural resistance to the passage of heat in large quantities, whereas the lighter and thinner materials used today generally have a low resistance to the transfer of heat. Therefore to maintain a comfortable and healthy internal temperature the external fabric of a building must be constructed of a combination of materials which will provide an adequate barrier to the transfer of heat.
Thermal insulation of buildings will give the following advantages: Reduction in the rate of heat loss. Lower capital costs for heating equipment. Lower fuel costs Reduction in the risk of pattern staining Reduction of condensation and draughts thus improving the comfort of the occupants. Less maintenance and replacement costs of heating equipment.
BUILDING REGULATION Building regulation L1 states that reasonable provision shall be made for the conservation of fuel and power in buildings. The requirements of this regulation can be satisfied by limiting the areas of roof lights and windows and by not exceeding the maximum U values for elements which are given in Approved Document L. The document gives the maximum thermal transmittance coefficient or U value for various situations. U value are expressed in W / m2 K, which is the rate of heat transfer in watts (joules/s) through 1m2 of the structure for one unit of temperature difference between the air on the two sides of the structure. To calculate a U value the complete constructional detail must be known together with the following thermal properties of the materials and voids involved: Thermal conductivity This is represented by the symbol λ (lambda). It is the measure of a material’s ability to transmit heat and is expressed as the energy flow in watts per square meter of surface area for temperature gradient of one Kelvin per meter conductivity, i.e. W/m K Surface or standard resistance These are value for surface and airspace (cavity) resistance. They vary with direction of energy floe, building elevation, surface emissivity and degree of exposure. They are expressed in the same units as thermal resistance and in calculations they are represented by:
Rsi Rso Ra
= surface resistance inside = surface resistance outside = surface resistance of the air space
[Note: value for λ and R can be obtained from tables published by the Chartered Institution of Building Services Engineers or product manufacturers’ catalogues.] To calculate the U value of any combination of materials the total resistance of the structure is found and then the reciprocal of this figure will give the required value. If an element of structure is not homogeneous – e.g. lightweight concrete block work with dense mortal joints or timber framing with insulation infilling cold bridging will occur through the denser parts. This must be allowed for and is known as the proportional area calculation, which is incorporated in the wall U value computation from Fig. 8.2.1. The proportional area calculation is not applied to the brick outer leaf, as the thermal resistance values for mortal and bricks are similar, i.c. a difference less than 1.0 m2 K/W.
Block wall proportional area calculation Standard block nominal area= 450 X 225 = 101, 250 mm2 Standard block format area = 440 X 215 = 94, 600 mm2 Difference or mortal area = = 6, 650 mm2
Proportional area= 6,650 = 0.0656 or 6.56% 101,250 Block area to total area is: 1- 0,0656 = 0.9344 or 93.44%
Thermal resistance (R = m/λ)
Inner leaf (cold-bridging portion) Plaster Mortal Insulation Rsi Ra ΣR = 0.026 = 0.125 = 1.515 = 0.120 = 0.090 = 1.876
Inner leaf (non-cold-bridging portion) Plaster Mortal Insulation Rsi Ra ΣR Outer leaf Brick Rso Ra ΣR U value = 0.121 = 0.060 = 0.090 = 0.271 = = = 0.396 W/m2 K The maximum U value requirements of building Regulations are shown diagrammatically in Fig. 8.2.2. Approved Document L of the Building Regulations gives details of 1 ΣR 1 (1.876 x 6.56%) + (2.277 x 93.44%) + (0.271 x 100%) = 0.026 = 0.525 = 1.515 = 0.120 = 0.090 = 2.277
necessary provisions regarding thermal insulation and specifies various materials and methods. The thermal insulation of roofs can be carried out at rafter level, beneath the covering or at ceiling level. Generally rafter level insulation will use more material but can be applied as a combined roofing felt and insulation thus saving labour cost. The roof void will be warm and on sheltered sites it should not be necessary to protect the cistern and pipe work against frost attack. Applying the insulation at ceiling level will reduce the amount of material required and will also reduce the heat loss into the roof space, but since the void is unheated the plumbing housed in the roof space will need insulating against freezing temperature (see fig. 8.2.2). Cold roofs will need to be ventilated to comply with Building Regulations F2.
ENERGY RATING OF DWELLINGS The government has established a Standard Assessment Procedure (SAP) for determining an energy rating for all new dwellings, including those created as a result of building work on an existing structure, i.e. house or other conversions to flats. The SAP incorporates a number of considerations, including incidental solar gains, ventilation characteristics, type of water heater, energy control system/accessories, fuel prices and type of thermal insulation applied to a building.
The energy efficiency of a dwelling can be rated anywhere on a scale from 1 to 100. Its precise evaluation is calculated by extracting data from tables and compiling worksheet, both provided in the Building Regulations, Approved Document L, Appendix G. There is no obligation to achieve a particular rating, but reference to Fig. 8.2.2. shows that a dwelling with a SAP rating of 60 or less will require higher levels of insulation for roof, ground floor and windows. This may be helpful for development of new dwellings in older buildings, where, for example, it is often impractical to attain contemporary insulation standards with older construction techniques such as solid masonry walls. Compliance may be achieved by satisfying either the Energy Rating, the Elemental or Target U Value Methods. Energy rating Method This is the calculated SAP rating for all new dwellings, including those created from conversions to existing buildings. The rating must fall in between 80 and 85 depending on the dwelling size: Floor area (m2) Up to 80 81-90 91-100 101-110 111-120 Over 120 Min. SAP rating 80 81 82 83 84 85
Elemental method This is satisfied if the thermal performances of the elements of construction conform to the criteria given in Fig. 8.2.2. Some possible applications are: Double glazing to all windows and glazed doors. External wall of cavity construction with 50 mm full or part full insulation. Ground floor fully insulated, typically with 50 mm rigid mineral wool.
Roof insulation between and possibly over the ceiling joists, with at least 150 mm of lightweight mineral wool.
[Note: Numerous other examples are acceptable. For further guidance see Appendix A Approved Document L to the Building Regulations and insulation product manufacture’s catalogues.] Target U value The previous methods can limit or restrain design, hence the need for this more flexible perspective for assessment. It makes use of incidentals such as variable glazed areas to accommodate solar gains, sophisticated energy management systems to control the internal environment and associated high efficiency water heaters. Calculations are essential to justify conformity and they must show that the Target U Value exceeds the Average U Value. Target U Value, where SAP is equal to or less than 60: Total floor area X 0.57 = Total area of exposed element Target U Value, where SAP is greater than 60: Total floor area X 0.57 = Total area of exposed element See Building Regulation, Approved Document L, Appendix F for application and worked examples. + 0.40 + 0.36
INSULATING MATERIALS When selecting or specifying thermal insulation materials the following must be taken into consideration: 1. Thermal resistance of the material 2. Need for a vapour control layer since insulating materials which become damp or wet, generally due to condensation, rapidly loose their insulation properties; therefore if condensation is likely to occur a suitable vapour control layer should be include the detail. Vapour control layers should always be located on the warm side of the construction. 3. Availability of material chosen. 4. Ease of fixing or including the material in the general construction. 5. Appearance if visible. 6. Cost in relation to the end result and ultimate savings on fuel and/or heating installation. 7. Fire risk - all wall and ceiling surface must comply with the requirements of Building Regulation B2 – restriction of spread of flame over surface of walls and ceilings. Insulating materials are made from a wide variety of materials and are available in a number of forms; Insulating concrete Basically a concrete of low density containing a large number of
voids. This can be achieved by using lightweight aggregates such as clinker, foam slag, expanded clay, sintered pulverized fuel ash, exfoliated vermiculite and expanded perlite, or alternatively an aerated concrete made by the introduction of air or gas into the mix. No fines concrete made by using lightweight or gravel aggregates between 20 and 10 mm size and omitting the fine aggregate is suitable for load bearing walls. Generally lightweight insulating concrete is used in the form of an in-situ screed to structural roof or as lightweight concrete block for walls.
Loose fills Material which can be easily poured from a bag and levelled off between the joists with a shape template. Materials include exfoliated vermiculite, fine glass fibrewool, mineral wool and cork granules. The depth required to satisfy current legislation is usually well above the top level of ceiling joists, therefore this type of insulation is now better used as a vertical fill between stud framing to dormer windows and walls in loft conversions. Most loose fills are rot and vermin proof as well as being classed as non-combustible. Boards Used mainly as dry linings to walls and ceilings either for self finish or direct decoration. Types include metallized polyester lined plasterboard, woodwool slab, expanded polystyrene boards, thermal backed (expanded polystyrene/extruded polystyrene) plasterboard and fibreboards. Insulating fibreboards should be conditioned on site before fixing to prevent buckling and distortion after fixing. A suitable method is to expose the boards on all sides so that the air has a free passage around the sheets for at least 24hours before fixing. During this conditioning period the boards must not be allowed to become wet or damp. Quilts Made from glass fibre or material wool bonded or stitched between outer paper covering for easy handling. The quilts are supplied in rolls from 6.000 to 13.000 m long and cut to suit standard joist spacings. They are laid between and over the ceiling joists and can be obtained in two thickness, 100 mm for general use and 150 mm for use in roof spaces. They can be placed in two layers, the lower layer between the joists with another superimposed at right angles to the joists. Insulating plasters Factory produced premixed plasters which have lightweight perlite and vermiculite expanded minerals as aggregates, and require only the addition of clean water before application. They are only one-third the weight of sanded plasters, have three times the thermal insulation value and are highly resistant to fire. However, they can only be considered as a supplement to other insulation products as they have insufficient thickness to provide full insulation.
Foamed cavity fill
A method of improving the thermal insulation properties of an
external cavity wall by filling the cavity wall with urea-formaldehyde resin foamed on site. The foam is formed using special apparatus by combining urea-formaldehyde resin, a hardener, a foaming agent and warm water. Careful control with the mixing and application is of paramount importance if a successful result is to be achieved; specialist contractors are normally employed. The foam can be introduced into the cavity by means of 25 mm bore holes spaced 1.000 m apart in all directions or by direct introduction into the open end of the cavity. The foam is a white cellular material containing approximately 99% by volume of air with open cells. The foam is considered to be impermeable and therefore unless fissures or cracks have occured during the application it will not constitute a bridge of the cavity in the practical sense. Non-combustible waterrepellent glass or rock wool fibres are alternative cavity fill material. Manufacture’s approved installers use compressors to blow the fibres into new or existing cavity walls where both iner and outer leaves are constructed of masonry. The application of cavity fill must comply with the requirement of Building Regulation D1. The most effective method of improving thermal comfort conditions within a building is to ensure that be inside surface is at a reasonably high temperature and this is best achieved by fixing insulating materials in this position. Thermal insulation for buildings other than dwelling are also contained in the Building Regulation under Part L. These are considered in Advanced Construction Technology.
THERMAL BRIDGING
Consistency of construction in the external elements is desirable to achieve a uniform heat transfer. It is, nevertheless, impractical to build in uniform layers and the routine is interrupted with ‘bridges’ between air voids across solids such as timber in frame walls. This result in variations in thermal transmittance values (see proportional area calculation – previous chapter) which should be avoided as much as possible. Examples include metal or dense concrete lintels and gaps in the continuity of cavity insulation. Where this does occur, the thermal or cold bridge will incur a cooler surface temperature than the remainder of the wall, greater heat loss at this point and a possible dew point temperature manifesting in water droplets or condensation. The moisture will attract dust and dirt to contrast with adjacent clean areas. This is known as pattern staining. The Approved Document to Part L of the Building Regulation makes specific reference to thermal bridging, indicating the areas most exposed. Further reference to the Building Regulation support document, Thermal insulation: avoiding risks – 2nd editions provides numerous examples of acceptable forms of construction at vulnerable place. Apart from examples of bad practice, such as using bricks to make up coursing in lightweight insulating concrete block inner leaf walls, the most common areas for thermal bridging are around door and window opening, junction between ground floor and wall, and the junction between wall and roof. These are shown in Fig. 8.3.1. As a measure of the significance of thermal bridging, the following formula can be applied: 0.3 X total length of opening surrounds + Average U value Total exposed surface areas [Note: Worked examples for calculating the average U value can be found in Appendix F of Approved Document L to the Building Regulations.]
DRAUGHT PROOFING
Draught proofing is required to prevent the infiltration of cold external air through leakage in the building envelope. It is also to limit heat losses through breaks in the continuity of construction. The areas most exposed occur at the junction of different component in the same element, e.g. door and window abutments with walls, access hatches into the roof space or eaves cupboards etc. the fit between window sashes and frame, and door and frame, are also very vulnerable to air leakage. The closeness of fit should be the subject of quality control at the point of manufacture, but this alone is insufficient to satisfy Part L of the Building Regulations. All opening units should have purpose-made seals or draught excluders. Particular attention must be provided at the points where service pipes and ducts penetrate the structure. Gaps must be god with appropriate filling and a flexible sealant applied between pipe or duct and adjacent filling. Dry linings, too, must receive special attention. It is not sufficient to secure these to background walls with only plaster dabs. Continuous plaster seals are required at abutments with walls, floors, ceiling and opening for service, windows and doors. Some areas and methods of treatment are shown in Fig.8.4.1.
CONCLUSIONS
Thermal insulation is hot current natural hindrance, from region high temperature to region average temperature or low. In this matter building is usually happens from exterior to part in a building The transfer of heat can happen in three ways: Conduction – hot weather flow passes solid goods, especially thing that Convection – hot delivery in gas or caused by move it air particle that be
can easily channel hot, ingredient example from iron, steel. less thick liquid when heated and increase is to setting on current or circulation. Radiation – hot transfer passes hot distribution or usually called with
radiation, or hot transfer passes emission that pass air. So that hot can be felled according to comprehensive.
The advantages of thermal insulation in building: Reduction in the rate of heat loss. Lower capital costs for heating equipment. Lower fuel costs Reduction in the risk of pattern staining Reduction of condensation and draughts thus improving the comfort of the occupants. Less maintenance and replacement costs of heating equipment.
Examples of thermal bridging include metal or dense concrete lintels and gaps in the continuity of cavity insulation. Where this does occur, the thermal or cold bridge will
incur a cooler surface temperature than the remainder of the wall, greater heat loss at this point and a possible dew point temperature manifesting in water droplets or condensation As a measure of the significance of thermal bridging, the following formula can be applied: 0.3 X total length of opening surrounds + Average U value Total exposed surface areas [Note: Worked examples for calculating the average U value can be found in Appendix F of Approved Document L to the Building Regulations.] Air current proofing wanted to prevent cold air infiltration outside passes building gap. This can also take outside hot limit pass aftermath building
Thermal insulation may be defined as a barrier to the natural flow of heat from an area of high temperature to an area of flow temperature. In building this flow is generally from interior to the exterior. Heat is a from of energy consisting of the ceaseless movement of tiny particles of matter called molecules; if these particles are moving fast they collide frequently with one another and the substance becomes hot. Temperature is the measure of hotness and should not be confused with heat. The transfer of heat can occur in three ways: Conduction – vibrating molecules come into contact with adjoining molecules and set them vibrating faster and hence they become hotter; this process is carried on throughout the substance without appreciable displacement of the particles. Convection – transmission of heat within a gas or fluid caused by the movement of particles which become less dense when heated and rise thus setting up a current or circulation. Radiation – heat is considered to be transmitted by radiation when it passes from one point to another without raising the temperature of the medium through which it travels. In a building all three methods of heat transfer can take place since the heat will be conducted through the fabric of the building and dissipated on the external surface by convection and/ or radiation. The traditional thick and solid building materials used in the past had a natural resistance to the passage of heat in large quantities, whereas the lighter and thinner materials used today generally have a low resistance to the transfer of heat. Therefore to maintain a comfortable and healthy internal temperature the external fabric of a building must be constructed of a combination of materials which will provide an adequate barrier to the transfer of heat.
Thermal insulation of buildings will give the following advantages: Reduction in the rate of heat loss. Lower capital costs for heating equipment. Lower fuel costs Reduction in the risk of pattern staining Reduction of condensation and draughts thus improving the comfort of the occupants. Less maintenance and replacement costs of heating equipment.
BUILDING REGULATION Building regulation L1 states that reasonable provision shall be made for the conservation of fuel and power in buildings. The requirements of this regulation can be satisfied by limiting the areas of roof lights and windows and by not exceeding the maximum U values for elements which are given in Approved Document L. The document gives the maximum thermal transmittance coefficient or U value for various situations. U value are expressed in W / m2 K, which is the rate of heat transfer in watts (joules/s) through 1m2 of the structure for one unit of temperature difference between the air on the two sides of the structure. To calculate a U value the complete constructional detail must be known together with the following thermal properties of the materials and voids involved: Thermal conductivity This is represented by the symbol λ (lambda). It is the measure of a material’s ability to transmit heat and is expressed as the energy flow in watts per square meter of surface area for temperature gradient of one Kelvin per meter conductivity, i.e. W/m K Surface or standard resistance These are value for surface and airspace (cavity) resistance. They vary with direction of energy floe, building elevation, surface emissivity and degree of exposure. They are expressed in the same units as thermal resistance and in calculations they are represented by:
Rsi Rso Ra
= surface resistance inside = surface resistance outside = surface resistance of the air space
[Note: value for λ and R can be obtained from tables published by the Chartered Institution of Building Services Engineers or product manufacturers’ catalogues.] To calculate the U value of any combination of materials the total resistance of the structure is found and then the reciprocal of this figure will give the required value. If an element of structure is not homogeneous – e.g. lightweight concrete block work with dense mortal joints or timber framing with insulation infilling cold bridging will occur through the denser parts. This must be allowed for and is known as the proportional area calculation, which is incorporated in the wall U value computation from Fig. 8.2.1. The proportional area calculation is not applied to the brick outer leaf, as the thermal resistance values for mortal and bricks are similar, i.c. a difference less than 1.0 m2 K/W.
Block wall proportional area calculation Standard block nominal area= 450 X 225 = 101, 250 mm2 Standard block format area = 440 X 215 = 94, 600 mm2 Difference or mortal area = = 6, 650 mm2
Proportional area= 6,650 = 0.0656 or 6.56% 101,250 Block area to total area is: 1- 0,0656 = 0.9344 or 93.44%
Thermal resistance (R = m/λ)
Inner leaf (cold-bridging portion) Plaster Mortal Insulation Rsi Ra ΣR = 0.026 = 0.125 = 1.515 = 0.120 = 0.090 = 1.876
Inner leaf (non-cold-bridging portion) Plaster Mortal Insulation Rsi Ra ΣR Outer leaf Brick Rso Ra ΣR U value = 0.121 = 0.060 = 0.090 = 0.271 = = = 0.396 W/m2 K The maximum U value requirements of building Regulations are shown diagrammatically in Fig. 8.2.2. Approved Document L of the Building Regulations gives details of 1 ΣR 1 (1.876 x 6.56%) + (2.277 x 93.44%) + (0.271 x 100%) = 0.026 = 0.525 = 1.515 = 0.120 = 0.090 = 2.277
necessary provisions regarding thermal insulation and specifies various materials and methods. The thermal insulation of roofs can be carried out at rafter level, beneath the covering or at ceiling level. Generally rafter level insulation will use more material but can be applied as a combined roofing felt and insulation thus saving labour cost. The roof void will be warm and on sheltered sites it should not be necessary to protect the cistern and pipe work against frost attack. Applying the insulation at ceiling level will reduce the amount of material required and will also reduce the heat loss into the roof space, but since the void is unheated the plumbing housed in the roof space will need insulating against freezing temperature (see fig. 8.2.2). Cold roofs will need to be ventilated to comply with Building Regulations F2.
ENERGY RATING OF DWELLINGS The government has established a Standard Assessment Procedure (SAP) for determining an energy rating for all new dwellings, including those created as a result of building work on an existing structure, i.e. house or other conversions to flats. The SAP incorporates a number of considerations, including incidental solar gains, ventilation characteristics, type of water heater, energy control system/accessories, fuel prices and type of thermal insulation applied to a building.
The energy efficiency of a dwelling can be rated anywhere on a scale from 1 to 100. Its precise evaluation is calculated by extracting data from tables and compiling worksheet, both provided in the Building Regulations, Approved Document L, Appendix G. There is no obligation to achieve a particular rating, but reference to Fig. 8.2.2. shows that a dwelling with a SAP rating of 60 or less will require higher levels of insulation for roof, ground floor and windows. This may be helpful for development of new dwellings in older buildings, where, for example, it is often impractical to attain contemporary insulation standards with older construction techniques such as solid masonry walls. Compliance may be achieved by satisfying either the Energy Rating, the Elemental or Target U Value Methods. Energy rating Method This is the calculated SAP rating for all new dwellings, including those created from conversions to existing buildings. The rating must fall in between 80 and 85 depending on the dwelling size: Floor area (m2) Up to 80 81-90 91-100 101-110 111-120 Over 120 Min. SAP rating 80 81 82 83 84 85
Elemental method This is satisfied if the thermal performances of the elements of construction conform to the criteria given in Fig. 8.2.2. Some possible applications are: Double glazing to all windows and glazed doors. External wall of cavity construction with 50 mm full or part full insulation. Ground floor fully insulated, typically with 50 mm rigid mineral wool.
Roof insulation between and possibly over the ceiling joists, with at least 150 mm of lightweight mineral wool.
[Note: Numerous other examples are acceptable. For further guidance see Appendix A Approved Document L to the Building Regulations and insulation product manufacture’s catalogues.] Target U value The previous methods can limit or restrain design, hence the need for this more flexible perspective for assessment. It makes use of incidentals such as variable glazed areas to accommodate solar gains, sophisticated energy management systems to control the internal environment and associated high efficiency water heaters. Calculations are essential to justify conformity and they must show that the Target U Value exceeds the Average U Value. Target U Value, where SAP is equal to or less than 60: Total floor area X 0.57 = Total area of exposed element Target U Value, where SAP is greater than 60: Total floor area X 0.57 = Total area of exposed element See Building Regulation, Approved Document L, Appendix F for application and worked examples. + 0.40 + 0.36
INSULATING MATERIALS When selecting or specifying thermal insulation materials the following must be taken into consideration: 1. Thermal resistance of the material 2. Need for a vapour control layer since insulating materials which become damp or wet, generally due to condensation, rapidly loose their insulation properties; therefore if condensation is likely to occur a suitable vapour control layer should be include the detail. Vapour control layers should always be located on the warm side of the construction. 3. Availability of material chosen. 4. Ease of fixing or including the material in the general construction. 5. Appearance if visible. 6. Cost in relation to the end result and ultimate savings on fuel and/or heating installation. 7. Fire risk - all wall and ceiling surface must comply with the requirements of Building Regulation B2 – restriction of spread of flame over surface of walls and ceilings. Insulating materials are made from a wide variety of materials and are available in a number of forms; Insulating concrete Basically a concrete of low density containing a large number of
voids. This can be achieved by using lightweight aggregates such as clinker, foam slag, expanded clay, sintered pulverized fuel ash, exfoliated vermiculite and expanded perlite, or alternatively an aerated concrete made by the introduction of air or gas into the mix. No fines concrete made by using lightweight or gravel aggregates between 20 and 10 mm size and omitting the fine aggregate is suitable for load bearing walls. Generally lightweight insulating concrete is used in the form of an in-situ screed to structural roof or as lightweight concrete block for walls.
Loose fills Material which can be easily poured from a bag and levelled off between the joists with a shape template. Materials include exfoliated vermiculite, fine glass fibrewool, mineral wool and cork granules. The depth required to satisfy current legislation is usually well above the top level of ceiling joists, therefore this type of insulation is now better used as a vertical fill between stud framing to dormer windows and walls in loft conversions. Most loose fills are rot and vermin proof as well as being classed as non-combustible. Boards Used mainly as dry linings to walls and ceilings either for self finish or direct decoration. Types include metallized polyester lined plasterboard, woodwool slab, expanded polystyrene boards, thermal backed (expanded polystyrene/extruded polystyrene) plasterboard and fibreboards. Insulating fibreboards should be conditioned on site before fixing to prevent buckling and distortion after fixing. A suitable method is to expose the boards on all sides so that the air has a free passage around the sheets for at least 24hours before fixing. During this conditioning period the boards must not be allowed to become wet or damp. Quilts Made from glass fibre or material wool bonded or stitched between outer paper covering for easy handling. The quilts are supplied in rolls from 6.000 to 13.000 m long and cut to suit standard joist spacings. They are laid between and over the ceiling joists and can be obtained in two thickness, 100 mm for general use and 150 mm for use in roof spaces. They can be placed in two layers, the lower layer between the joists with another superimposed at right angles to the joists. Insulating plasters Factory produced premixed plasters which have lightweight perlite and vermiculite expanded minerals as aggregates, and require only the addition of clean water before application. They are only one-third the weight of sanded plasters, have three times the thermal insulation value and are highly resistant to fire. However, they can only be considered as a supplement to other insulation products as they have insufficient thickness to provide full insulation.
Foamed cavity fill
A method of improving the thermal insulation properties of an
external cavity wall by filling the cavity wall with urea-formaldehyde resin foamed on site. The foam is formed using special apparatus by combining urea-formaldehyde resin, a hardener, a foaming agent and warm water. Careful control with the mixing and application is of paramount importance if a successful result is to be achieved; specialist contractors are normally employed. The foam can be introduced into the cavity by means of 25 mm bore holes spaced 1.000 m apart in all directions or by direct introduction into the open end of the cavity. The foam is a white cellular material containing approximately 99% by volume of air with open cells. The foam is considered to be impermeable and therefore unless fissures or cracks have occured during the application it will not constitute a bridge of the cavity in the practical sense. Non-combustible waterrepellent glass or rock wool fibres are alternative cavity fill material. Manufacture’s approved installers use compressors to blow the fibres into new or existing cavity walls where both iner and outer leaves are constructed of masonry. The application of cavity fill must comply with the requirement of Building Regulation D1. The most effective method of improving thermal comfort conditions within a building is to ensure that be inside surface is at a reasonably high temperature and this is best achieved by fixing insulating materials in this position. Thermal insulation for buildings other than dwelling are also contained in the Building Regulation under Part L. These are considered in Advanced Construction Technology.
THERMAL BRIDGING
Consistency of construction in the external elements is desirable to achieve a uniform heat transfer. It is, nevertheless, impractical to build in uniform layers and the routine is interrupted with ‘bridges’ between air voids across solids such as timber in frame walls. This result in variations in thermal transmittance values (see proportional area calculation – previous chapter) which should be avoided as much as possible. Examples include metal or dense concrete lintels and gaps in the continuity of cavity insulation. Where this does occur, the thermal or cold bridge will incur a cooler surface temperature than the remainder of the wall, greater heat loss at this point and a possible dew point temperature manifesting in water droplets or condensation. The moisture will attract dust and dirt to contrast with adjacent clean areas. This is known as pattern staining. The Approved Document to Part L of the Building Regulation makes specific reference to thermal bridging, indicating the areas most exposed. Further reference to the Building Regulation support document, Thermal insulation: avoiding risks – 2nd editions provides numerous examples of acceptable forms of construction at vulnerable place. Apart from examples of bad practice, such as using bricks to make up coursing in lightweight insulating concrete block inner leaf walls, the most common areas for thermal bridging are around door and window opening, junction between ground floor and wall, and the junction between wall and roof. These are shown in Fig. 8.3.1. As a measure of the significance of thermal bridging, the following formula can be applied: 0.3 X total length of opening surrounds + Average U value Total exposed surface areas [Note: Worked examples for calculating the average U value can be found in Appendix F of Approved Document L to the Building Regulations.]
DRAUGHT PROOFING
Draught proofing is required to prevent the infiltration of cold external air through leakage in the building envelope. It is also to limit heat losses through breaks in the continuity of construction. The areas most exposed occur at the junction of different component in the same element, e.g. door and window abutments with walls, access hatches into the roof space or eaves cupboards etc. the fit between window sashes and frame, and door and frame, are also very vulnerable to air leakage. The closeness of fit should be the subject of quality control at the point of manufacture, but this alone is insufficient to satisfy Part L of the Building Regulations. All opening units should have purpose-made seals or draught excluders. Particular attention must be provided at the points where service pipes and ducts penetrate the structure. Gaps must be god with appropriate filling and a flexible sealant applied between pipe or duct and adjacent filling. Dry linings, too, must receive special attention. It is not sufficient to secure these to background walls with only plaster dabs. Continuous plaster seals are required at abutments with walls, floors, ceiling and opening for service, windows and doors. Some areas and methods of treatment are shown in Fig.8.4.1.
CONCLUSIONS
Thermal insulation is hot current natural hindrance, from region high temperature to region average temperature or low. In this matter building is usually happens from exterior to part in a building The transfer of heat can happen in three ways: Conduction – hot weather flow passes solid goods, especially thing that Convection – hot delivery in gas or caused by move it air particle that be
can easily channel hot, ingredient example from iron, steel. less thick liquid when heated and increase is to setting on current or circulation. Radiation – hot transfer passes hot distribution or usually called with
radiation, or hot transfer passes emission that pass air. So that hot can be felled according to comprehensive.
The advantages of thermal insulation in building: Reduction in the rate of heat loss. Lower capital costs for heating equipment. Lower fuel costs Reduction in the risk of pattern staining Reduction of condensation and draughts thus improving the comfort of the occupants. Less maintenance and replacement costs of heating equipment.
Examples of thermal bridging include metal or dense concrete lintels and gaps in the continuity of cavity insulation. Where this does occur, the thermal or cold bridge will
incur a cooler surface temperature than the remainder of the wall, greater heat loss at this point and a possible dew point temperature manifesting in water droplets or condensation As a measure of the significance of thermal bridging, the following formula can be applied: 0.3 X total length of opening surrounds + Average U value Total exposed surface areas [Note: Worked examples for calculating the average U value can be found in Appendix F of Approved Document L to the Building Regulations.] Air current proofing wanted to prevent cold air infiltration outside passes building gap. This can also take outside hot limit pass aftermath building
