What is an air permeability test?

Air permeability test Explained

As well as air tightness testing, air infiltration and permeability testing are also recognised as air leakage. Newly constructed or developed buildings must be tested for airtightness. Keep in mind that ventilation is not the same thing as air leakage.

A building envelope that is airtight with the ventilators closed is described as being airtight in Approved Document F, Ventilation.

An envelope with greater airtightness will have a lower infiltration rate.

According to them, the ability of an airtight fabric to allow air through is measured by its air permeability.

A rate of air leakage per square metre of envelope area is defined as air leakage per hour over the area of the envelope at a differential pressure differential of 50 Pascal (50 N/m2). During the design stage, the target value of air permeability is determined.

The legislation was introduced in the UK in April 2002 enforcing airtightness standards.

Besides reducing running costs, it would also ensure the quality of materials, components, and workmanship; prevent uncomfortable drafts, and avoid condensation problems.

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How an air permeability test is performed

What is an air permeability test?

The building envelope permeability (air pressure, airtightness, infiltration, or blower door testing) is measured at 50 Pascal (50 N/m2) test pressure differential across the building envelope, which is used as a benchmark to determine the per cubic metre air leakage rate.

A door, designed to incorporate a fan, is usually mounted into the frame of an external door opening.

In order to determine the permeability of the building envelope (given that its area is known), the fan extracts air from the building envelope from which the exterior and internal pressures are determined.

By measuring how well-sealed a building is, and whether or not it contains any openings, one can determine whether or not it is properly sealed. In order to conduct tests, fires must be extinguished, windows and doors must be shut, and ventilators must be sealed.

According to the building regulations, the testing method required of dwellings is ATTMA TSL1 and for non-dwellings is ATTMA TSL2.

There is an airtightness testing and measurement association called ATTMA. On behalf of the government, the ATTMA is responsible for creating the testing standards.

The regulations set a limiting air permeability of 10 m-3.h-1.m-2@50Pa, metres cubed, per hour, per metre squared of external building envelope area.

In order to comply with these standards, buildings’ Building Emission Rates (BERs) or Dwelling Emission Rates (DERs) must be calculated based upon the assessed air permeability of the dwellings and not exceed the Target Emission Rate (TER).

TER is calculated using the target value of the air permeability. In order to establish the BER or DER, the assessed air permeability is measured.

Air pressure testing

Testing is required on all residential developments this may be a sample of units and non-dwellings.

There may be an exemption for buildings with a useful floor area of less than 500m2. The calculations should be based on the assessed air permeability.

Where the air permeability of a specific unit is not tested for a large development, the air permeability that is assessed is based on the average of other units of the same type on the development.

Building regulations & advice

Air leakage testing & thermography tests

It may be impractical to test the whole compartmentalised building, so a representative area may be tested.

The air permeability test can be performed as part of a complete service (which can include SAP calculations, Energy Performance Certificates (EPCs) and an overall energy audit) or may be part of an isolated study.

To ensure that air leakage paths are correctly pinpointed, the test should not only be carried out as a compliance test but also include a detailed assessment of details and diagnostic tests like infrared thermography and smoke tests.