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Air Tightness Testing – The Three Levels Explained

The Three Levels of Air Tightness Testing – Explained

Air tightness testing, also known as air pressure testing, air permeability testing or air leakage testing, are tests designed to check the rate at which air leaks out of a property.

By installing powerful fans and bringing the internal pressure of the building to varying levels, air flow and leakage can be tested, finding the average leakage over the course of under two hours and structural weak points which might be contributing factors.

Since 2006 air testing has been part of government building regulations. Excess air leakage in a property causes increased heat loss, leading to colder properties, larger energy bills and a much higher CO2 impact.

Conversely, a lack of free air flow can cause excess condensation, damp or mould, which can lead to long term structural damage and put the occupants at risk.

Does my property need to be tested?

According to Approved Document L1A, domestic developments require a specific percentage of dwelling types to be air tested, as demonstrated in the table below.

No. of dwelling types Tests required
1 or 2 1
3 or 4 2
5 or greater 3

For commercial or other non-domestic buildings, ALL buildings over 500m2 must be tested.

Air Testing Level Specifics

Level 1: Pressure testing for single houses or small non-residential buildings up to 4000m3 internal envelope volume.

Level 1 tests are generally performed with a single blower fan installed in a standard doorway with maximum dimensions of 2.25m by 1.1m.

Level 2: Pressure testing for buildings over 4000m3, but not including Large and Complex High Rise (LCHR) or phased handover and zonal building types.

Larger buildings that require Level 2 tests need more specialised equipment, generally requiring a multi-fan blower system set up in one or more doors.

Level 3: Pressure testing for large buildings not included in Level 2 tests, including LCHR or zonal buildings.

Get a quote

If you need air tightness testing, our experienced engineers can assess your property, offering advice on the fastest and simplest ways for you to meet compliance standards. Contact us here to discuss your needs, or for an individual quote.

iATS Registered and UKAS Recognised


We are registered with iATS (Independent AirTightness Testing Scheme) and use equipment calibrated by UKAS laboratories. Our testing procedures are also recognised by UKAS.