Air Tightness Testing​

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What is Air Tightness Testing?

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.


Air leakage is the uncontrolled flow of air through gaps and cracks in the fabric (often referred to as infiltration or draughts) and not ventilation, which is the controlled flow of air in and out of the building.


Too much air leakage leads to unnecessary heat loss and discomfort for the occupants. As the Government strives to reduce CO2 emissions from new buildings, building regulations now place greater emphasis on the quality of the fabric of the building.

How is the Air Tightness Testing done?​

  All testing is completed under the strict methods prescribed by ATTMA (Air Tightness Testing Measurement Association) technical guidelines. A fan or a number of fans are installed into a suitable external opening (usually the entrance door) and the entire building is pressurised over a range of pressure difference.


Before we arrive on site though it’s important for us to accurately calculate the building external envelope to reflect the conditioned space within the completed building.


The testing is measured in air flow m3 over an average hour period at an average of 50Pa for every m2 of building fabric. 

Before the test is carried out, passive ventilation must be temporarily sealed. HVAC plant is switched off and temporarily sealed. The exterior envelope and all its openings are closed. Internally all doors are temporarily fixed open. Drainage traps should be filled.


Site workers can remain in the building during the test, or will have to remain outside until the test is complete. There are no health risks to site workers who remain in the building during the test; however there may be some discomfort from the fan noise.  


When is the Air Test needed?

To meet the minimum standards set out in Approved Document L1A, on each domestic development, an air pressure test should be carried out on three units of each dwelling type or 50% of all instances of that dwelling type, whichever is less. 

Approved Document L2A requires all non-domestic buildings over 500m2 to be tested.


The actual test results need to be better than the estimated figure specified in the design SAP or SBEM. There is an exemption for testing smaller sites and non-domestic building less than 500m2, however, this automatically triggers a more stringent target to be proved by calculation.


Getting Started

Having your building air tested need not be hassle. At NSL we like to be involved with projects as early as possible to ensure no hiccups on test day.