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FAQ
Airtightness testing
Do you need to test?
New buildings other than dwellings as described by Part L2A:
For buildings with a total useful floor area less than 500m²-
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Either Airtightness test carried out in accordance with ATTMA TS1
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Or an air permeability rate of 15m³h-¹/m² at 50Pa used in the calculation of the BER
For buildings with a total useful floor area greater than 500m²:
Mandatory Airtightness test carried out in accordance with ATTMA TS1
New dwellings as described by Part L1A:
Mandatory Testing required on:
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Dwellings to be tested should be selected by Building Control
Small developments consisting of 1 or 2 dwellings:
The Developer should:
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Demonstrate that the same dwelling type built on a previous development within the past 12 months was tested and met the design air permeability.
Or -
Avoid testing but use a value of 15m³/hr.m-2 when calculating the BER
What is building air leakage?
Air Leakage is the uncontrolled flow of outside air into and out of a building.
It is not planned by the designers and is due to imperfections in the building ‘envelope’ (or outer skin). This should not be confused with “ventilation” which is the controlled flow of air into and out of the building through purpose built venilators. Too much air leakage will have detrimental effects on the buildings thermal performance, comfort levels and energy efficiency. In addition a leaky construction may result in the exfiltration of warm moist air, which may lead to interstitial condensation and consequential deterioration of the building fabric.
Uncontrolled air leakage will typically take place through:
- joints, gaps and cracks in the construction
- gaps created where the structure penetrates the outer skin of the building
- cracks around door and window openings
- gaps where services enter the building
What’s involved in achieving a good level of airtightness?
Careful design, specification, quality control during construction and performance testing the building will achieve an airtight building envelope.
Design:
The building form, position and types of opening, interaction of the structure and airtight layer all effect the air leakage performance. An appropriate airtightness specification must be selected. The line of the airtight barrier should be identified as soon as possible allowing examination of details at openings and junctions in the envelope.
Build Check provide a drawing review service
Specification:
The components and systems that make up the external envelope such as curtain walling, windows, cladding etc must achieve at least the specified level of airtightness set for the building. Responsibilities for dealing with coordination at junctions should be clearly spelt out.
Construction:
All supervisory staff and subcontractors should be adequately briefed on the importance of maintaining the airtight barrier, quality control and reproduction of the designers details.
Build Check provide training seminars, site induction programmes and pre-test inspections
Airtightness, what standard should my building achieve?
The airtightness of buildings as defined in Part L of the building regulations is based on Air Permeability where the envelope area is defined as the area of the walls, roof and ground floor slab. For improved energy efficiency and much better control of the indoor environment better airtightness standards are required than those required by Part L. The following table (ref: ATTMA TS1) provides current normal and best practice airtightness criteria for different building types:
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By good design, attention to detail and good levels of quality control on site 10 m3/(hr.m2) should be achieved with minimal additional expense.
U-Value simulations
Information required to undertake thermal simulation of windows, doorsets and other building components.
Build Check Ltd provide a thermal simulation service for building components to meet the requirements of the Building Regulations, Part L. These include:
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Windows and Doors to BS EN 10077 Parts 1 & 2
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Cavity closures to IP12 and 17
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Curtain walling systems
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Building Envelope
The client can have an analysis on a job specific basis or use standard configurations to cover product range.
To calculate the thermal transmittance of a window or door in accordance with BS EN ISO 10077-1:2000 and EN ISO 10077-2:2003, certain information is required.
The client must provide the following information:
- 1:1 scale electronic drawings, in DXF format, of the window or door internal elevation.
- 1:1 scale electronic drawings, in DXF format, of the frame cross-sections.
- Electronic drawing of glazing spacer bar, in DXF Format, (if not incorporated in cross sectional drawings)
We recommend that details of the spacer bar materials, conductance and configuration are included.
Alternatively, a value can be attributed to certain spacer bars and glazing configurations from tables in the Standard. However, these values may be more onerous and have a limited range of application.
Please label:
- All internal and external environments on the drawing.
- All components of the frame sections and glazing with the material type (e.g. softwood, PVC, aluminium, butyl, EPDM etc).
- All weather seals material/conductance.
- All sealant material/conductance
In addition:
- Provide details of glazing system type (e.g. 4-16-4).
- With any Low-E coatings used, state whether the emissivity value is 'normal' or corrected.
- To calculate a BFRC rating we require UKAS accredited air Leakage results @50 Pa for the applicable window system and g-factor (more commonly known as Solar Heat Gain Coefficient) of the glazed unit.
Thermal conductance of materials
The table below contains details of some of the materials used in the construction of windows and doors and their associated thermal conductance (this list is not exhaustive).
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