Admin


Design Fabric

How It Works

How It Works

It is important that each element of the design fabric and fixed building specification are compliant, and that the administrator has used their version of SAP to prove that each element of the design specification used to set the standard in the building control system is compliant by calculating a SAP Assessment which shows the DER is less than the TER.

The design fabric can be input into the design fabric section of the online building control system in two ways. It can be imported from the design information calculators in the design section of the system directly into the building control system and the online documentation and onsite compliance documents will automatically populated by the design fabric specification which is proven to be compliant. The advantage of importing from the calculator is that the design decisions made in the calculator are supported by good detail, best practice and compliance documentation specific for a project.

The design fabric specification can be input manually without using the calculator. If this is the case, the administrator should ensure that the design team on the project can provide the builder with good detail, best practice and compliance documents, ensuring the specification can be practically delivered to site by the builder.

When the construction detail and best practice buttons for each element of the design fabric are pressed in the design fabric section of the system, the stakeholder but more especially the builder will be provided with construction detail and a description of how best to deliver the design fabric specification to site.

1.0 Design Floor

Best Practice

1.0 Ground Floor

When considering which materials and typical details to use for the floor- the Designer should study the Construction Detail and technical data provided by this section of the system. The advice given is based on the "Fabric First" approach, technical data supplied and Foresites’ experience of designing and project managing energy efficient domestic buildings.

Which insulators and typical floor details are used for the full fill method

Insulators: There are two insulators used in the UK to insulate floors Expanded Polystyrene- Polyurethene/polyisoyarate. If building to the 2010 building regulations or better, Foresite recommend that the high density insulator Polyurethene/polyisoyarate with a better thermal conductivity is used.

Typical details: There are three typical details that can be used when constructing a floor slab: The insulation over the slab or under the slab, and a suspended timber floor slab. Foresite recommend that the suspended timber floor slab should be avoided, not because the U Value of the timber suspended floor but because this type of floor is hard to make air tight, for this reason the option is not provided in the design section of the system.

How to use the floor U Value calculator for the full fill method

The U value calculator will automatically provide the Designer with a recommended specification depending on the level of performance required. If the Designer wants to improve on this he can use the floor U value calculator for the full fill method of construction, when increasing the depth of the insulator in the calculator, the Designer should ensure the depth that is being input can technically be achieved.

The materials used in this floor calculator are suited to this method of construction, and Foresite are constantly introducing new materials to their calculators if the Designer believes that other materials should be introduced to the calculator please contact us on tech@foresitebuildingcontrol.co.uk

The integrity of the floor insulation for the full fill method

It is important that the floor insulation is installed correctly and that there are no gaps were sheets are butted together and at corners. It is important that a 50mm perimeter strip is used at all the exposed walls and that the strip has a minimum thermal conductivity of 0.025W/m2K. The cavity wall for full fill needs to be below the DPC level so it is important that the cavity insulation used will not absorb water and is breathable.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with the floor slab onsite compliance document which will have every element of the design floor specification on it, the builder should only tick the integrity of the insulation box if the described specification is equalled or better by what has been actually used on site and if the quality of the workmanship is good. The integrity of the floor insulation should be checked by the other registered stakeholders involved in the project.

the Designer should use this compliance document as prove of compliance and should input what has be shown on this document when inputting the floor data into their version of SAP, if this document is not provided the Designer should use a default figure of when calculating a Floor U value.

The thermal bridge floor detail for the full fill method

It is important that the builder constructs the floor slab as per the floor detail provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with the floor slab onsite compliance document which will have every element of the design floor specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The quality of the y factor floor detail should be checked by the other registered stakeholders involved in the project.

The air tight floor detail required for the full fill method

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the floor provided by the onsite floor compliance document that can be viewed on line by the builder.

The builder needs to tape and seal around all the services that come through the ground floor slab and make sure that the services are in the correct position, if services need to be moved the DPM will damaged causing air leakage. The DPM or air barrier needs to be taken above the DPC and an air tight seal needs to be made between the DPM and the air barrier being used to the walls.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the checklist at each junction, this will improve the chance of the complete building reaching the design air permeability.

Foresite are constantly adding new details and materials to this section of the system. assessors who are registered can contact us with details of new materials and details to tech@foresitebuildingcontrol.co.uk

Construction Detail

Drawing Junction Description View
FF/1.1a Exposed perimeter insulation below slab
FF/1.1b Exposed perimeter insulation above slab
FF/1.1c Exposed perimeter suspended floor slab
FF/1.2a Party Wall Junction insulation below slab
FF/1.2b Party Wall Junction insulation above slab
FF/1.2c Party Wall Junction suspended floor slab
Standard: 2010 Depth
Structural material :
Screed :
Floor insulation (main insulator) :
Area of floor slab :
Exposed perimeter :

2.0 Design Walls

Best Practice

2.0 External walls

When considering which materials and typical details to use for the walls of full fill- The designer should study the Construction Detail and technical data provided by this section of the system. The advice given is based on the "Fabric First" approach, technical data supplied and Foresites experience of designing and project managing energy efficient buildings.

Which insulators and typical wall details are used for the full fill method

Insulators: There are many breathable, non-water absorbent insulators that can be used to fill the cavity of the full fill method of construction. Most of these insulators have similar thermal conductivity values, the decision on which material to use will depend on cost and sustainability. The Rockwool and Glass wool would be easy to use and cost effective but not very sustainable; The natural materials would be easy to use and sustainable but more expensive.

Bonded bead is another product that could be used, it is cost effective and would be more sustainable that the Rockwool but not as sustainable as the natural materials, its biggest advantage would be integrity of the insulation whereas the integrity of the other materials is dependent on the workmanship of the block layer which would require more supervision.

An improvement on the U value can be made by using insulated boards internally and by spraying breathable spray foam on the internal walls, if this is done the designer should check the technical data supplied by the manufactures to see if a vapour barrier is required.

Typical details: There are two typical details that can be used at intermediate floor level concrete floor and timber joist floor, the rule of thumb is that domestic buildings use joists and apartments use concrete slabs. If using concrete the builder should consider using block and beam as a continuous air barrier and insulation is more easily constructed by leaving a void with the blocks.

The wall details at the eaves used are dependent on the type of building. If the building has a flat ceiling, a dormer roof, a 1.5 storey or a flat roof. The designer has the choice of using the ACD for openings or use the Foresite details, the latter have better thermal bridge values and will give a better y factor value.

How to use the Wall U Value calculator for the full fill method

The Wall U value calculator will automatically provide the designer with a recommended specification depending on the level of performance required. If the designer wants to improve on this he can use the wall U value calculator for the full fill method of construction, when increasing the depth of the insulation in the calculator, the designer should ensure the depth that is being input can technically be achieved.

The materials used in this wall calculator are suited to this method of construction, and Foresite are constantly introducing new materials to their calculators if the design or supervising professional who is a member believes that other materials should be introduced to the calculator please contact us on tech@foresitebuildingcontrol.co.uk

The integrity of the Wall insulation for the full fill method

It is important that the chosen wall insulation is installed correctly, if using insulation being installed by the block layer, then this work needs to be checked regularly ensuring the insulation is installed correctly and that the cavity is free of all debris and checks should also be made at the following junctions Exposed Ground Floor; Intermediate Floor Level; around the openings and at the Eaves. If using Bonded Bead ensure the installer provides a quality assurance checklist.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with intermediate floor, opening details and eave onsite compliance documents which will have every element of the design wall specification on it, the builder should only tick the integrity of the insulation box if the described specification is equalled or better by what has been actually used on site and if the quality of the workmanship is good. The integrity of the wall insulation should be checked by the other registered stakeholders involved in the project.

The energy assessor should use this compliance document as prove of compliance and should input what has be shown on this document when inputting the wall data into their version of SAP.

The thermal bridge wall details for the full fill method

It is important that the builder constructs the intermediate floor, wall openings and eaves as per the typical details detail provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with intermediate floor, opening and eave onsite compliance document which will have every element of the design wall specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project.

The air tight wall detail required for the full fill method

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the wall details provided by the onsite floor compliance document that can be viewed on line by the builder.

The builder needs to tape and seal around all the services that come through the wall and great care should be taken around the wall openings to windows and doors. If using timber joists, joist hangers should be used and if using concrete slabs block and beam should be considered, these choices will make it easier to make the building air tight.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Foresite are constantly adding new details and materials to this section of the system. Construction professionals who are members can contact us with details of new materials and details to tech@foresitebuildingcontrol.co.uk

Construction Detail

Drawing Junction Description View
FF/2.1a Exposed intermediate timber floor
FF/2.1b Exposed intermediate concrete floor
FF/2.2a Party wall intermediate timber floor
FF/2.2b Party wall intermediate concrete floor
FF/6.1 Exposed external wall coner
FF/6.2 Exposed internal wall corner
FF/6.3 Party Wall corner
Standard: 2010 Depth
External Finish :
External Leave :
Cavity Insulation (main insulator) :
Internal Leave :
Internal Finish & Improvement :

3.1 Design Flat Ceiling

Best Practice

3.1 Flat Ceiling

When considering which materials and typical details to use for the flat ceiling- the Designer should study the Construction Detail and technical data provided by this section of the system. The advice given is based on the "Fabric First" approach, technical data supplied and Foresites experience of designing and project managing energy efficient buildings.

Which insulators and typical flat ceiling details are used for the full fill method

Insulators: There are many breathable, non-water absorbent insulators that can be used to insulate the roof of the full fill method of construction. Most of these insulators have similar thermal conductivity values, the decision on which material to use will depend on cost and sustainability. The Rockwool and Glass wool would be easy to use and cost effective but not very sustainable; the natural materials would be easy to use and sustainable but more expensive. Blown natural material like wool is another product that could be used on flat ceilings, it is cost effective and very sustainable.

Typical details: There are three typical details that can be used with the flat ceiling the flat ceiling eave detail; the exposed gable ceiling detail and the party wall gable detail.

How to use the roof U Value calculator for the full fill method

The roof U value calculator will automatically provide the Designer with a recommended specification depending on the level of performance required. If the Designer wants to improve on this he can use the roof U value calculator for the full fill method of construction, when increasing the depth of the insulation in the calculator, the Designer should ensure the depth that is being input can technically be achieved.

The materials used in this wall calculator are suited to this method of construction, and Foresite are constantly introducing new materials to their calculators if the Designer believes that other materials should be introduced to the calculator please contact us on tech@foresitebuildingcontrol.co.uk

The integrity of the wall insulation for the full fill method

It is important that the chosen flat roof insulation is installed correctly, the integrity of the insulation can easily be checked visually, the only issue with the flat ceiling insulation is to maintain the continuity width at the eave detail. There are a couple of things that are needed to maintain the width at the eaves:

  • Ventilate the roof above the rafter, by cross battening the roof battens; this gives an extra depth of roof void that can be insulated. See diagram
  • If using fabricated roof trusses make sure that the roof rafters are cantilevered well over the wall plate, this will give extra roof void that can be insulated. See diagram 1.
  • If cutting the roof and using the wall plate as the main bearing point for the roof rafter, the wall plate will need to be at a high level, raising the block work to this level will not be stable, we suggest that the wall plate is on top of the ceiling rafters, this will need to be structurally checked by an engineer. See diagram 2.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with the eave and gable wall onsite compliance documents which will have every element of the design flat ceiling specification on it, the builder should only tick the integrity of the insulation box if the described specification is equalled or better by what has been actually used on site and if the quality of the workmanship is good. The integrity of the flat ceiling insulation should be checked by the other registered stakeholders involved in the project.

the Designer should use this compliance document as prove of compliance and should input what has be shown on this document when inputting the flat ceiling data into their version of SAP, if this document is not provided the Designer should use a default figure of when calculating a wall U value.

The thermal flat ceiling detail for the full fill method

It is important that the builder constructs the flat ceiling eave detail and gable wall details as per the typical details provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with flat ceiling eave and gable ceiling onsite compliance documents which will have every element of the design flat ceiling specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project.

The air tight flat ceiling detail required for the full fill method

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the flat ceiling details provided by the onsite floor compliance document that can be viewed on line by the builder.

The builder needs to tape and seal around all the services that come through the flat ceiling. If the flat ceiling has a lot of services and down lighters it might be hard to make the building air tight by following the flat ceiling (profile), the design team should consider running the insulation and air barrier up the rafter and do the (ridge) see sketches. It would be cheaper to follow the profile of the flat ceiling as the exposed need to be insulated.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Foresite are constantly adding new details and materials to this section of the system. assessors who are registered can contact us with details of new materials and details to tech@foresitebuildingcontrol.co.uk.

Construction Detail

Drawing Junction Description View
FF/3.1 Exposed eave for bungalow,2 storey
FF/4.1 Exposed gable ceiling detail
FF/4.2 Party wall gable ceiling detail
Standard: 2010 Depth
Ceiling Centers :
Insulation between joists :
Insulation over joists :

3.2 Design Sloping Ceiling

Best Practice

3.2 Sloped Ceiling

When considering which materials and typical details to use for the flat ceiling- the Designer should study the Construction Detail and technical data provided by this section of the system. The advice given is based on the "Fabric First" approach, technical data supplied and Foresites experience of designing and project managing energy efficient buildings.

Which insulators and typical sloped ceiling details are used for the full fill method

Insulators: There are many breathable, non-water absorbent insulators that can be used to insulate between the rafters of the 0sloping roof for the full fill method of construction. Most of these insulators have similar thermal conductivity values, the decision on which material to use will depend on cost and sustainability. The Rockwool and Glass wool would be easy to use and cost effective but not very sustainable; the natural materials would be easy to use and sustainable but more expensive.

A new product is breathable spray foam it is more expensive and its sustainability would not be as good as the natural materials but its integrity of installation would be very good and it also acts as air barrier.

The void between the sloping roof rafters are limited and the Designer might consider improving the performance of the sloping roof by adding insulated boards or indeed any of the roof insulators to the underside of the rafter, the Designer should check the technical data to see if vapour barriers are required and what depths of materials are available when using the sloping roof calculator. The vapour barrier can also act as an air tight barrier.

Typical details: There are six typical details that can be used with the sloped ceiling the dormer and 1.5 storey eave detail; the exposed gable ceiling detail and the party wall gable detail, the exposed rafter detail and the party rafter detail. To understand were these details are in a building go to the input section of the calculator.

How to use the sloped roof U Value calculator for the full fill method

The roof U value calculator will automatically provide the Designer with a recommended specification depending on the level of performance required. If the Designer wants to improve on this he can use the roof U value calculator for the full fill method of construction, when increasing the depth of the insulation in the calculator, the Designer should ensure the depth that is being input can technically be achieved.

The materials used in this wall calculator are suited to this method of construction and the sloping roof U value calculator allows the Designer improve the performance of the roof internally. Foresite are constantly introducing new materials to their calculators if the Designer believes that other materials should be introduced to the calculator please contact us on tech@foresitebuildingcontrol.co.uk.

The integrity of the sloped ceiling insulation for the full fill method

It is important that the chosen sloped roof insulation is installed correctly, the integrity of the insulation needs to be checked before the air tight barrier is installed, there is also an issue with the sloped ceiling insulation is to maintain the continuity width at the eave detail. There are a couple of things that are needed to maintain the width at the eaves:

  • Ventilate the roof above the rafter, by cross battening the roof battens; this gives an extra depth of roof void that can be insulated. See diagram
  • If using fabricated roof trusses make sure that the roof rafters are cantilevered well over the wall plate, this will give extra roof void that can be insulated.
  • If cutting the roof and using the wall plate as the main bearing point for the roof rafter, the wall plate will need to be at a high level, raising the block work to this level will not be stable, we suggest that the wall plate is on top of the ceiling rafters, this will need to be structurally checked by an engineer.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with the eave, gable and rafter onsite compliance documents which will have every element of the design sloped ceiling specification on it, the builder should only tick the integrity of the insulation box if the described specification is equalled or better by what has been actually used on site and if the quality of the workmanship is good. The integrity of the sloped ceiling insulation should be checked by the other registered stakeholders involved in the project.

the Designer should use this compliance document as prove of compliance and should input what has be shown on this document when inputting the sloped ceiling data into their version of SAP, if this document is not provided the Designer should use a default figure of when calculating a roof U value.

The thermal sloped ceiling detail for the full fill method

It is important that the builder constructs the sloped ceiling, eave details, gable wall details and rafter details as per the typical details provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with sloped ceiling eave, gable ceiling and rafter onsite compliance documents which will have every element of the design sloped ceiling specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project.

The air tight sloped ceiling detail required for the full fill method

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the sloped ceiling details provided by the onsite sloped floor compliance documents that can be viewed on line by the builder.

The builder needs to tape and seal around all the services that come through the sloped ceiling. If the ceiling has a lot of services and down lighters it might be hard to make the building air tight by following the sloped ceiling (profile), the design team should consider running the insulation and air barrier up the rafter and do the (ridge) see sketches.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Foresite are constantly adding new details and materials to this section of the system. assessors who are registered can contact us with details of new materials and details to tech@foresitebuildingcontrol.co.uk.

Construction Detail

Drawing Junction Description View
FF/3.2 Expoesd eave dormer
FF/3.3 Exposed eave 1.5 storey
FF/3.4a Exposed eave to actual dormers
FF/3.4b Exposed valleys
FF/5.1 Exposed rafter detail at gable
FF/5.2 Party wall rafter detail at gable
Standard: 2010 Depth
Rafter Centers :
Insulation Between Joists :
Improvement Internally :

3.3 Design Flat Roof

Best Practice

3.3 Flat Roof

When considering which materials and typical details to use for the flat roof- the Designer should study the Construction Detail and technical data provided by this section of the system. The advice given is based on the "Fabric First" approach, technical data supplied and Foresites experience of designing and project managing energy efficient buildings.

Which insulators and typical flat roof details are used for the full fill method

Insulators: There are many breathable, non-water absorbent insulators that can be used to insulate the roof of the full fill method of construction. Most of these insulators have similar thermal conductivity values, the decision on which material to use will depend on cost and sustainability. The Rockwool and Glass wool would be easy to use and cost effective but not very sustainable; the natural materials would be easy to use and sustainable but more expensive. Anew product should be considered breathable spray foam it is expensive and not very sustainable but it also act as an air barrier.

Typical details: There are two typical details that can be chosen for the flat roof a parapet detail soffit and facia detail.

How to use the roof U Value calculator for the full fill method

The roof U value calculator will automatically provide the Designer with a recommended specification depending on the level of performance required. If the Designer wants to improve on this he can use the roof U value calculator for the full fill method of construction, when increasing the depth of the insulation in the calculator, the Designer should ensure the depth that is being input can technically be achieved.

The materials used in this wall calculator are suited to this method of construction, and Foresite are constantly introducing new materials to their calculators if the Designer believes that other materials should be introduced to the calculator please contact us on tech@foresitebuildingcontrol.co.uk.

The integrity of the roof insulation for the full fill method

It is important that the chosen flat roof insulation is installed correctly, the integrity of the insulation can easily be checked visually before the air tight membrane or vapour barrier is fixed.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with the eave onsite compliance documents which will have every element of the design flat roof specification on it, the builder should only tick the integrity of the insulation box if the described specification is equalled or better by what has been actually used on site and if the quality of the workmanship is good. The integrity of the flat roof insulation should be checked by the other registered stakeholders involved in the project.

the Designer should use this compliance document as prove of compliance and should input what has be shown on this document when inputting the flat ceiling data into their version of SAP, if this document is not provided the Designer should use a default figure of when calculating a wall U value.

The thermal flat roof detail for the full fill method

It is important that the builder constructs the flat roof eave detail as per the typical details provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with flat ceiling eave onsite compliance documents which will have every element of the design flat roof specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project.

The air tight flat roof detail required for the full fill method

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the flat roof details provided by the onsite roof compliance document that can be viewed on line by the builder. The builder needs to tape and seal around all the services that come through the flat roof.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Foresite are constantly adding new details and materials to this section of the system. assessors who are registered can contact us with details of new materials and details to tech@foresitebuildingcontrol.co.uk.

Construction Detail

Drawing Junction Description View
FF/5.3a Flat roof detail with facia
FF/5.3b Flat roof detail with parapet
Standard: 2010
Rafter Centers : Depth
Insulation Between Joists :
Improvement Internally & Externally :

4.1 Design Windows

Best Practice

4.0 Windows & Doors

Options:

The performance of windows is usually only considered in terms of their whole window U value, but other considerations need to be taken into account when considering what windows to use, the heat transmission (U Value) its air infiltration (L Value) and solar Heat gains (g value). Windows are an example of looking at the performance against cost and the law of diminishing returns, when the performance of a 0.8w/m2K window and a 1.5 W/m2K window are used to calculate the DER the increase in performance of the dwelling by using the more expensive high performance window is minimal. For more information on window performances go to www.bfrc.org

The thermal bridge around openings.

It is important that the builder constructs the wall opening detail as per the typical details provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

The main heat loss at construction junctions are at windows and doors, good construction details at the head, jamb, sills and thresholds can greatly reduce the thermal bridge or y factor of a building. Foresite have designed head, jamb and sill details that when used in conjunction with the Scottish Full Fill Cavity ACDs will reduce the y factor from being less than 0.08 W/m2K to less than 0.04 W/m2K for a dwelling. These Foresite details have been calculated using recognised software to a BR 497 standard and can be used to calculate an as constructed DER if compliance documents are provided to the assessor

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with wall opening onsite compliance documents which will have every element of the wall opening specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project. If compliance documents are not provided to the Designer a default figure of 0.15 W/m2K can only be used.

The air tight details around windows.

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the wall openings provided by the onsite roof compliance document that can be viewed on line by the builder.

The main infiltration of air is at window reveals and the seals to the window and door openings. Whichever method is used to make the building air tight attention to detail is important around the reveals. An agreement should be made with the window installer that any breaks in the seals of the windows that are found while the building is being air tested should be rectified by them.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Construction Detail

Drawing Junction Description View
FF/7.1 Lintel at window & door head
FF/7.1a Foresite lintel at window & door
FF/7.2 Jamb at window and door
FF/7.2a Foresite jamb at window & door
FF/7.3 cill at window
FF/7.3a Foresite cill at window
Standard: NONE U Value (W/m2k)
NONE 0

4.2 Design Doors

Best Practice

4.0 Windows & Doors

Options:

The performance of windows is usually only considered in terms of their whole window U value, but other considerations need to be taken into account when considering what windows to use, the heat transmission (U Value) its air infiltration (L Value) and solar Heat gains (g value). Windows are an example of looking at the performance against cost and the law of diminishing returns, when the performance of a 0.8w/m2K window and a 1.5 W/m2K window are used to calculate the DER the increase in performance of the dwelling by using the more expensive high performance window is minimal. For more information on window performances go to www.bfrc.org

The thermal bridge around openings.

It is important that the builder constructs the wall opening detail as per the typical details provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

The main heat loss at construction junctions are at windows and doors, good construction details at the head, jamb, sills and thresholds can greatly reduce the thermal bridge or y factor of a building. Foresite have designed head, jamb and sill details that when used in conjunction with the Scottish Full Fill Cavity ACDs will reduce the y factor from being less than 0.08 W/m2K to less than 0.04 W/m2K for a dwelling. These Foresite details have been calculated using recognised software to a BR 497 standard and can be used to calculate an as constructed DER if compliance documents are provided to the assessor

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with wall opening onsite compliance documents which will have every element of the wall opening specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project. If compliance documents are not provided to the Designer a default figure of 0.15 W/m2K can only be used.

The air tight details around windows.

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the wall openings provided by the onsite roof compliance document that can be viewed on line by the builder.

The main infiltration of air is at window reveals and the seals to the window and door openings. Whichever method is used to make the building air tight attention to detail is important around the reveals. An agreement should be made with the window installer that any breaks in the seals of the windows that are found while the building is being air tested should be rectified by them.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Construction Detail

Drawing Junction Description View
FF/7.4a Threshold insulation below slab
FF/7.4b Threshold insulation above slab
FF/7.4c Suspended timber floor
Standard: NONE U Value (W/m2k)
NONE 0

4.3 Design Rooflights

Best Practice

4.0 Windows & Doors

Options:

The performance of windows is usually only considered in terms of their whole window U value, but other considerations need to be taken into account when considering what windows to use, the heat transmission (U Value) its air infiltration (L Value) and solar Heat gains (g value). Windows are an example of looking at the performance against cost and the law of diminishing returns, when the performance of a 0.8w/m2K window and a 1.5 W/m2K window are used to calculate the DER the increase in performance of the dwelling by using the more expensive high performance window is minimal. For more information on window performances go to www.bfrc.org

The thermal bridge around openings.

It is important that the builder constructs the wall opening detail as per the typical details provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

The main heat loss at construction junctions are at windows and doors, good construction details at the head, jamb, sills and thresholds can greatly reduce the thermal bridge or y factor of a building. Foresite have designed head, jamb and sill details that when used in conjunction with the Scottish Full Fill Cavity ACDs will reduce the y factor from being less than 0.08 W/m2K to less than 0.04 W/m2K for a dwelling. These Foresite details have been calculated using recognised software to a BR 497 standard and can be used to calculate an as constructed DER if compliance documents are provided to the assessor

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with wall opening onsite compliance documents which will have every element of the wall opening specification on it, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project. If compliance documents are not provided to the Designer a default figure of 0.15 W/m2K can only be used.

The air tight details around windows.

It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction details in the building, so it is important that the builder follows all the air tight instructions for the wall openings provided by the onsite roof compliance document that can be viewed on line by the builder.

The main infiltration of air is at window reveals and the seals to the window and door openings. Whichever method is used to make the building air tight attention to detail is important around the reveals. An agreement should be made with the window installer that any breaks in the seals of the windows that are found while the building is being air tested should be rectified by them.

Compliance: Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability.

Standard: NONE U Value (W/m2k)
NONE 0

5.0 Design Thermal Bridge

Best Practice

5.0 Thermal Bridge

What is thermal bridge?

A simplified description is the loss of heat through the construction joints, so the more complicated a building is, the more heat will be lost through these joints. The measure of the heat loss for a particular building is calculated by taking a psi value for a construction joint and multiplying this value by the length of the joint, this process is repeated for all the construction joints in the building and they are added together: this result is then divided by the total exposed area of the Floor; Wall and roof: this is the y factor that is used to calculate the DER.

It is very important to measure the y factor in this way because if a default figure is used when a certain set of Accredited Details are used, it penalises good design because badly designed building will be allowed to use the same default figure. The calculator allows the Designer to calculate the y factor for an individual project and will give a printout of how it was calculated.

Options: The calculator at the moment gives the Designer two options, to use the wall opening details used by the Full fill Scottish Accredited Details or use the Foresite wall opening details that have been accredited using approved software to a BR 429 standard.

Workmanship required for the thermal bridge detail: It is important that the builder constructs all the typical details as per the drawings provided by the building control system and if the builder is in any doubt as to what is required, if he goes to the as constructed section of the building control system he will get a detailed description of what is required from viewing online or downloading the onsite compliance document.

The key to building energy efficient buildings is the attention to detail and supervision of the workmanship, this system can produce good detail and compliance documents but it is up to the builder to construct the detail as per the drawing, the detail then needs to be supervised and recorded.

Compliance: As part of the Foresite building control system, it is important that the builder downloads the customised compliance documents from the as constructed section of the system. The building control system will automatically provide the builder with the detail on how to construct the y factor for all construction joints in the onsite compliance documents, the builder should only tick the y factor box if the detail shown has been completed as per the generic drawing shown and with good workmanship. The detail and quality of the y factor detailing should be checked by the other registered stakeholders involved in the project. If compliance documents are not provided to the Designer, a default figure of 0.15 W/m2K can only be used when calculating the DER.

Design Y-Factor : W/m²K
5a

6.0 Design Air Permeability

Best Practice

6.0 Air Permeability

Three main options for the Full Fill Method of construction:

  • 1. A coat of plaster on both the external and internal block walls reduces air infiltration, but the builder will need to use air tight membrane and tapes at the construction joints. It is cost effective but will be difficult to get air exchanges of less than 5 m3/m2/hr. with this method.
  • 2. Forming a service cavity on the internal wall and using an air tight membrane with tapes at the construction joints, this is the most common method and exchanges of less than 2m3/m2/hr. can be achieved with uncomplicated designs, but the membrane is susceptible to damage from other trades.
  • 3. Spraying a breathable foam on the internal block work, is a relatively new method and exchanges of less than 2m3/m2/hr. can be achieved with even complicated designs, it is a robust air barrier and costs are similar to the membrane system.

Critical areas of infiltration:

The main areas were air infiltration can occur are at the construction joints and in particular around the window and door reveals, when the building is being tested the seals to the windows and doors should be tested especially if low air exchanges are required.

  • Service penetrations in the floor slab can be resolved by accurately locating the service ducts in the floor slab and sealing the services with the DPM, Foresite believe the Designer should provide setting out drawings for services which will help the builder position the service ducts in the correct position.
  • Seals between the DPM and the air barrier in the walls especially at corners can be problematic and will require good workmanship. Seals between the wall barriers which in this case is the parge coat and an air tight membrane at eave and ceiling level will also require good workmanship.
  • Sealing around outlet switches and plates, were the electrical cables are chased into the wall a heavier coat should be applied in these areas and especially were electrical boxes are fitted ensuring no leakage.
  • Air infiltration through the ceilings by hatch excess, plumbing, electric lights and recessed down lighters can cause a significant source of heat loss. Proprietary products are available that can be used to seal many of these penetrations. Detail guidance on achieving airtight ceilings is given in BS 9250: 2007-Code of practice for design of ceilings in pitched roofs.
  • Extract Fans and service penetrations in the wall, this can be resolved by building the services into the wall and following the procedures outlined in the service drawing, the extract fans should be fitted with external flaps to minimise air in filtration.

Other problematic areas are roof lights and hatches into uninsulated voids; if the procedures outlined in these attached drawings are followed air infiltration will be greatly reduced. The problem of services and hatches can be eliminated in flat ceilings by running the insulation and air barrier up the roof rafter to the ridge

Forming an air tight barrier:

The aim is to form an air tight barrier or envelope with the exposed fabric of the building. The designer has two choices with the air tight barrier and insulation: To follow the profile of the roof or go up the rafter straight to the ridge and back down.

When considering how to make the ceiling air tight, the most common method for a flat external ceiling is to run the insulation and air tight membrane along the flat ceiling, problems can arise sealing hatches, plumbing, electric’s especially recessed lights when this system is used. These issues can be resolved by running the insulation and airtight membrane up the rafter, this would mean that sealing hatches, plumbing is no longer a required. This would also mean that exposed walls such as gables would need to be insulated up to the ridge and barges.

When to carry out an air test:

It is impossible to make the Part L1A of the building regulation compliant with the fabric first approach without attempting to get the air exchanges down to less than 6 m3/m2/hr. and to prove this a blower door test needs to be carried out.

With the introduction of the new building regulations in 2010 and with the target of zero carbon by 2016, the air testing of all dwellings is going to be necessary to prove compliance. All air permeability tests should be carried out to the standards outlined in the publication Measuring Air Permeability of building envelopes produced by ATTMA, if a blower door test is not forwarded to the administrator/assessor then a default figure of 10 m3/m2/hr. 50 Pascal’s can only be used to calculate the as constructed DER.

Foresite recommend that the builder should carry out a blower door test after the building has been made air tight and before the plasterboard has been fitted, the plasterboard should not be fitted until such time as the dwelling has at least achieved its design permeability. The builder is encouraged to improve on the design permeability and if they do it will be recorded by the air test and rewarded in the as constructed DER.

Compliance: It is important that the as constructed air permeability is at least equal to the design air permeability, this can only be achieved by attention to detail by the builder at all the construction points in the building, so it is important that the builder follows all the air tight instructions for all the construction joints, this detailed is provided by the onsite roof compliance document that can be viewed on line by the builder.

Compliance can only be proven when an air test is carried out on the completed building, but it is important that the builder goes through the check list at each junction; this will improve the chance of the complete building reaching the design air permeability. If air test are not carried out the Designer can only use a default figure of 10m3/m2/hr. to calculate the as constructed DER

Standard: NONE m3/m2.hr
NONE 0

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