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.

What is Air Tightness Testing

What is Air Tightness Testing?

Air leakage, air permeability and air tightness are all terms that refer to the uncontrolled loss of air from inside a building to the outside and the infiltration of air coming from outside to inside. This loss or gain of air through cracks, holes or gaps in the fabric of the building is often felt to us as draughts through air leakage paths.

blower door

Trying to achieve a good level of air tightness is important for the energy efficiency of the building. The benefits of improved insulation and more energy efficient heating systems are lost if warm air simply leaks out of the building and cold air can leak in. Poor air tightness can be responsible for up to 40% of heat loss from buildings resulting in much higher heating costs I winter and cooling costs in summer.

It’s important to have an air tightness test completed on the property. This allows a figure – in m3/hr/m2) to be put on the amount of air gained and lost. The attained air leakage rate can then be measured against what’s acceptable and what’s not in the eyes of the building regulations. A good practice figure is currently set at 5m3/hr/m2 which is quite easy to achieve and can drastically reduce the ongoing heating costs of the building.

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