Ace the air leakage test for a hassle-free certification.


Why is air leakage important?

Minimising air leakage is good for the environment and for the client: if there are holes and gaps in the building fabric, heated air can escape. Reduced air leakage makes for an energy-efficient building, with lower CO2 emissions and – happily for the customer – lower energy bills.

And booking an air leakage test is the easiest way for your property to comply with Part L regulations. Skip the test, and your build will be automatically assigned a worst-case scenario value, equivalent to the property having a window permanently open. Having an air leakage test allows you to submit an accurate value, making for a better SAP rating overall.

All in all, an air leakage test might cost money, but a hassle-free certification is priceless.   


What does the test measure?

The test seeks to prevent the uncontrolled flow of air through gaps and cracks in the fabric of the building, caused by wind blowing against or across a building.

 The build is given an air permeability rating, which is found by dividing the amount of uncontrolled air leakage by the envelope area of the property. In practical terms, this is done by depressurising the space and measuring how much air is sucked into the building when the fan runs at 50 Pascals (50 Pa is about five times the pressure a low-level building might experience on a cold winter’s day).

In order to pass, a dwelling must achieve a minimum result of 10 m3/(h.m.2) – but the SAP Assessor may well design the building to achieve a lower value (perhaps 5m3/(h.m.2)). If so, then this lower value must be met if the SAP is to comply – otherwise the result would be classified as a ‘fail’.

Under Part L, plots not tested will be subjected to a +2.0 m3/(h.m2).

If the Air Test score is higher than mandated, the property will need to have remedial work carried out and then be retested. When we carry out the test, if a property fails its target we aim to stay while the issue is fixed, and we’ll always retest for no extra fee.

If the Air Test score meets requirements, the result is given to the SAP assessor who will update their calculations, prepare final reports and issue the EPC.


When is the test carried out?

The test can be carried out at any time, but it’s sensible to do it towards the end of the building process, when all elements that affect the air barrier have been completed and sealed – door frames, windows, skirting, loft hatches and so on. The test is concerned specifically with uncontrolled air leakage, meaning trickle vents, ventilation systems and extractor fans are excluded from consideration (they are taped up before the test begins).


What if my build involves several properties?

Part L specifies that a sample of buildings should be tested. It’s a good idea to book your Air Tester early, in that case, as they can work out how many tests will be needed and when to schedule them.


How can I prepare well for the test?

Preparation for the air leakage test starts right at the beginning, at the planning stage. It’s vital that all parties involved in your build have prioritised air tightness throughout – it can save much time and expense later on.

With that in mind, plan for regular inspections throughout the build, to ensure good practice. Don’t forget to seal blockwork for external walls before beginning studwork for partitions. Remember that air can create a ‘chimney effect’ behind plasterboard, moving between floors, and that when fitting suspended ceilings, the hidden ceiling should be well-sealed to prevent air flowing into the space.

Pay particular attention to problem areas: pipework to external services, boiler flues, radiator pipes, light fittings and other electricity cables, eaves cupboards, behind the bath panel, loft hatches, and of course the careful installation of windows and doors.

Consider running a test mid-build, before the airtight barrier has been covered up, so any necessary work can be carried out quickly. Then you can catch any potential problems early, before the test at completion.

Then, a final checklist:

  • Have all external doors and windows, the loft hatch, and the light switches and sockets been fitted?
  • Have integral garage doors been fitted with draught excluders?
  • Are extractor fans and trickle vents in place, and have these been taped up?
  • Have door frames, skirting, services, windows, and any pipework to external services been thoroughly sealed?
  • Are the walls completed and decorated?
  • Have you filled all traps with water for the test?

To book an air leakage test or to ask any questions, call us on 01454 317940 or email . We prepare carefully for each test and our method is proven and thorough: we’ll make the process as easy and straightforward as possible, so you can be well on your way to a successful build.


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