Air Tightness Testing is a vital component of building regulations and energy conservation initiatives. It quantifies the volume of conditioned air, either heated or cooled, that infiltrates and exits a building through uncontrolled leakage, essentially the air that seeps through openings or fractures in the building’s structure. This process involves the use of a calibrated fan, fitted into the building’s external envelope, which either introduces air into the property or extracts it, establishing a regulated pressure differential within the building. The air tightness tester employs calibrated instruments to determine the airflow entering or leaving the property. The findings from this air tightness test can pinpoint areas in a building that require remediation to enhance energy efficiency, diminish environmental footprint, and yield savings on energy expenses. It plays a pivotal role in building design and planning, aiding in the development of more eco-friendly homes and buildings.
Air tightness is quantified by evaluating the rate of air leakage per square meter of the building’s external envelope per hour, under an artificially induced pressure differential of 50 Pascals across the envelope. This method is employed to mimic conditions of higher wind pressure and to verify the robustness of the air tightness layer. The air leakage is denoted as Xm³/hr/m²@50Pa, a measurement standard adopted by the UK Building Regulations.
In contrast, the rate at which the air volume changes in the building per hour at 50 Pa is another method of measurement. This is expressed as Xach/hr@50Pa and is the preferred measure used by Passivhaus.
The common method for these measurements is the ‘blower door’ test. This involves installing a frame with a membrane in a doorway and placing a large fan in the middle of that membrane. The fan is used to blow air into the building, and the air flow into the building is then measured.
To create a controlled building pressure differential, a calibrated fan is fitted into the building’s external envelope. This fan either supplies air into or extracts air out of the property. The air tightness tester then uses calibrated equipment to calculate the air flow into or out of the property. This ensures accurate measurements of air tightness.
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)
Air tightness testing is performed by certified individuals who are part of a recognised Competent Persons Scheme. These professionals, referred to as air tightness testers, offer air tightness testing services and are employed by a member organisation. The scheme is overseen by bodies that have been authorised by the Department for Communities and Local Government (DCLG) and the Welsh government.
The Air Tightness Testing & Measurement Association (ATTMA) operates one such Competent Persons Scheme. Members of ATTMA are registered testers who undergo independent audits and certification. Their certification encompasses air tightness testing in accordance with the ATTMA Technical Standards (TSL1 &/or TSL2) and BS EN:13829 (2001). This certification enables ATTMA member companies to demonstrate their expertise, allowing them to conduct tests on both commercial and domestic properties in line with the relevant building regulations.
ATTMA’s authorisation is recognised by the governments of England, Northern Ireland, Scotland, and Wales. Furthermore, ATTMA is listed in the relevant Building Regulations as an authorised competent persons scheme for the air tightness testing industry.
ATTMA are committed to running impartial schemes. Our impartiality statement, GDPR data management, data, whistleblowing can be accessed using the links above. This also include ATTMA’s full complaints procedure if you are not happy with ATTMA’s service.
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