An air tightness test is also known as an air leakage test/Air Pressure Test. An air test will quantify the amount of uncontrolled air loss or gain through cracks, holes or gaps in the fabric of a building. These are felt as draughts and conversely, lead to heat loss.
An air test is usually carried out on completion of the building.
Air testing is a building regulation requirement. Approved Document Part L 1a sets out the applicable regulations for England and Wales.
Achieving a good level of air tightness is important for the energy efficiency of the building. Not only will it save on heating costs but it will reduce the impact of carbon emissions.
Good air tightness enhances the comfort of occupants and protects against airborne pollutants, dust and pollen.
The air test engineer will obtain the necessary information to complete the test. This includes the building dimensions and Design Air Permeability of the building.
The building is either pressurised or depressurised using a blower fan. Interval pressure readings are then taken within the building. These readings will ascertain how much air leakage there is in the building. The result of the test will be compared with the Design Air Permeability figure set by the SAP/SBEM assessor, and rated pass or fail.
The air test engineer will seal the applicable parts of the building, check U bend traps are filled with water, and make sure the building is fit for testing. (A Building Preparation Form can be downloaded from our website). A calibrated blower fan is fitted within an external door frame of the building and readings are recorded. Environmental readings, wind speed, air temperature and air pressure are taken as these influence the result. The engineer uses computer software to calculate the result.
The engineer is then able to produce a report and issue the certificate.
There is a minimum requirement that a building must achieve an Air Permeability result of 10m3/(h.m2)@50Pa. This represents the quantity of air leakage (m3 per hour) per m2 of the building envelope.
Refer to our Air Checklist for the full details
‘Build tight, ventilate right’.
The Communities and Local Government Accredited Construction Details (ACD) are an excellent point of reference.
If it fails, the engineer will advise on the potential leakage points. These can often be easily remedied on the day and then re-tested. If the problem is more substantial, a further re-test may need to be arranged on another day.
Any remedial work is usually completed by the builder, unless an arrangement is made with the testing engineer. There are often disclaimers in place for remedial works carried out by the engineer in relation to a non-guarantee of a test result passing.
Building Regulations Part L1A specifies that:
3.17 On each development an air pressure test should be carried out on three units of each dwelling type or 50 per cent of all instances of that dwelling type, whichever is less. For the purpose of this approved document, a block of flats should be treated as a separate development, irrespective of the number of blocks on the site. The dwelling(s) to be tested should be taken from the first completed batch of units of each dwelling type.
Note: Most larger developments include many dwelling types. Multiple units of each type should be tested to confirm the robustness of the designs and the construction procedures.
Outline of dwelling types:
Below is a formula for testing multiples of the same dwelling type:
|No. of Units Per House Type||Tests Required|
|1 or 2 of a single house type||1 Test|
|3 or 4 of a single house type||2 Tests|
|5 or More of a single house type||3 Tests|
The tested dwelling must then attain an Air Permeability rate of 2 or less, than the Design rate. If this does not occur, then further dwellings are tested.
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