What is Air Tightness Testing?

Air Tightness Testing is the process of measuring the amount of conditioned (heated or cooled) air entering and exiting a building through uncontrolled infiltration

How is Air Tightness Measured?

A calibrated fan is installed into the external envelope of the building and supplies air into, or extracts air out of, the property creating a controlled building pressure differential. The tester uses calibrated equipment and calculates an air flow into, or out of, the property. In simple terms, the amount of air going into, or out of the property when the building is subject to a pressure differential is the amount of ‘air leakage’.

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How are the Results Presented?

The results for air tightness tests can be presented in three different ways

Air Leakage, known as ‘Qpr’, is the amount of air entering or exiting the building at a given pressure.

In most countries, Q50 is used to denote the air leakage at a building pressure differential of 50 Pa. Units are m3.h-1 @ 50 Pa.

Air Permeability, known as ‘APpr’, is the amount of air leakage divided by the internal envelope area of the building.

In most countries, AP50 is used to denote the air permeability at a building pressure differential of 50 Pa. Units are m3.h-1.m-2 @ 50 Pa.

Air Changes per Hour, known as ‘Npr’, is the amount of air leakage divided by the internal volume of the building.

In most countries, N50 is used to denote the air changes per hour at a building pressure differential of 50 Pa. Units are m3.h-1.m-3 @ 50 Pa.

ATTMA Members are required to use ATTMA Lodgement which automatically creates their certificate (see image to the left)

Who is Authorised to Test?

For a testing organisation to show compliance with this standard they shall carry out their testing in an equitable manner and must remain independent of companies involved in the construction of the buildings they test.  They must also have suitable third party monitoring systems in place and this is demonstrated by either having an active membership with a CPS scheme, such as ATTMA or hold accreditation to ISO/IEC 1705:2017, or later

Authorised Levels

  • Level 1

    Air tightness tester able to test dwellings and non-dwellings up to 4000m³ gross envelope volume and tested as a single entity as stated in EN13829 2001, with a single blower door fan set, in line with training process undergone.

  • Level 2

    Air tightness tester able to test both simple and non-simple buildings, those being any buildings except those defined as large and complex, high rise (LCHR), or phased and zonal hand-over, as set out in the relevant NOS.

  • Level 3

    Testers who have been assessed for a higher level of expertise and also for LCHR buildings, phased and zonal hand-over. Level 3 testers may also be assessed as impartial scheme auditors (confidentiality, non-disclosure and conflicts of interest conditions will apply to this). There are currently no Level 3 Training Courses

  • Envelope Area Calculator

    A technician whose activity is to calculate building envelope areas, who has been assessed against the relevant NOS.

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The Air Tightness Testing & Measurement Association

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