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.

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