Air Tightness Testing

Testing for Air Tightness

Air tightness testing is a recognised method of measuring the extent to which air is lost through leaks in the building fabric. It is sometimes referred to as air leakage testing or air pressure testing. When testing for air tightness the pressure differential is measured across the envelope of the building be means of a large fan installed temporarily sealed and a range of static pressures and environmental readings are taken. The fan is switched on and the air pressure in the property is gradually increased or decreased and the differential pressure is recorded at each step. The total air flow required to achieve a pressure differential of 50 Pa is calculated and divided by the total building envelope area to provide the leakage rate in m3/hr/m2.


 On each development air tightness testing should be carried out on three units of each dwelling type or 50% of all the instances of that dwelling type, whichever is less. A block of flats should be treated as a separate development irrespective of the number of blocks on the site.

Depending on the size of the property, the duration of the air tightness test should take no longer than 2 hours with the air tightness test certificate issued some 2 days later.

It is best to make sure that the building is fully prepared for the air tightness test, in most cases the main areas of air leakage are through penetrations in the kitchen and/or utility room and through penetrations in the bathrooms and cloak rooms. Other common air leakage paths are through the wall/floor junction, light fittings and boilers rooms and service cupboards.

Our fan systems are compact, discreet and fit simply into a personnel door. The system can easily be transported through areas of limited access or up to high level areas. It is for this reason that many companies working in busy city centres utilise our expertise and equipment. We are able to eliminate the site disruption caused by the larger trailer type testing equipment. Work can also continue inside the building whilst the air leakage test is being carried out.

In the event of a building failing an air tightness test,  we can offer smoke testing, which highlights the areas of leakage in the building fabric. We can then undertake a full written and photographic survey as reference for your site management and relevant subcontractors. We will also offer free advice on the best method to seal any leaking areas. The main benefits of this are:

  • Air leakage is quickly identified in the event of a test failure
  • Remedial works can start straight away
  • Practical completion can be achieved more quickly

If you require air tightness testing or domestic ventilation testing, we have the knowledge and experience to ensure your building passes first time. If you require more information please contact me direct on 07775 623464 or e-mail me at:

How Is an Air Tightness Test Undertaken?

How is an air tightness test undertaken?

A temporary airtight screen is fitted into the entrance door of the dwelling with water traps filled (or temporarily blocked), trickle vents closed (sealed under Part L 2010) and extract vents sealed – we send out a full checklist to help our client prepare for the air tightness testing.

A fan is then mounted in the screen and operated to blow air into or out of the dwelling to create a pressure difference between inside and outside of approximately 50 Pa.


The air tightness of the dwelling is quantified by measuring the rate of airflow through the fan while a range of pressure differences between the inside and outside of the dwelling is maintained.

  1. Approved Document L sets out the applicable regulations for England and Wales.
  2. Approved Document L1A sets out the air tightness requirements for new dwellings.
  3. Approved Document L1B states that reasonable provision should be made for continuity but no test requirements in existing dwellings.
  4. Approved Document L2A deals with new buildings other than dwellings.
  5. Approved Document L2B provides that extensions to buildings (other than dwellings) where the extension/s

A dwelling must achieve an air permeability result of 10m3/hr/m2, however most instances this has now been reduced to 5m3/hr/m2.

The designed air permeability rate is defined in the design stage SAP and often imposes a more stringent target. If the tested air tightness result is greater than that used in the design stage SAP, the as-built SAP may not comply and you may fail the air tightness test.

A test that does not achieve a Building Regulations minimum performance requirement would be classed as a air tightness fail. Should tests fail to achieve the necessary performance level, the property may need a smoke test and thereafter once the air leakage paths are identified remedial sealing works can be undertaken with final re-testing. In some instance the you may be asked to test further examples of that dwelling type to restore confidence and show that remedial actions have been carried forward into the remainder of the build.

If you require air tightness testing on your project, please contact us at, or call me direct on 07775623464.