What is Air Tightness Testing?

Bookmark this
11 June, 2019 By Robert & Adam Joselyn

Air tightness testing, also known as an air leakage, air infiltration or air permeability testing is a test to indicate the cubic metres of air leakage per hour per square metre of external area of the building – (m3/hr.m2) – as per Part L of Building Regulations.

Air leakage can occur through gaps and cracks in the fabric of the building envelope, allowing heat to escape, thus driving up heating bills and C02 production. Part L of the Building Regulations now requires that a representative sample of all new-build domestic dwellings be tested for air leakage.

All of our tests are carried out in accordance with ATTMA TSL1 (domestic) or TLS2 (commercial) and all our engineers are trained and registered members of ATTMA.

Air tightness testing is an often overlooked part of building new houses. It applies to almost every new build dwelling, and a certificate must be held in order to get building control sign-off. At RJ Acoustics, we have been providing testing and consultancy since 2010.

We always make the testing process hassle free and over the years have experience in working with a variety of parties including large development companies, property owners, self-builders and much more, so you can rest assured we are able to deal with your needs effectively.

We make sure to carry out all work at your convenience and once complete, we always endeavour to get a certificate to you as soon as possible.



To complete an air tightness test we need access to an empty dwelling. We put a large fan in an expandable door frame, which goes into an external door in the house, normally the front door. All other external doors and windows will be closed and all internal doors kept open.

The fan will then typically depressurise (although you can also perform a pressurisation test) the house to a pressure of at least -50Pa. An anemometer reads the internal pressure, external pressure and the strength that the fan has to work at to create that pressure difference. 10 readings are taken at different pressures, and along with other factors such as barometric pressure and temperature, fed into software which calculates air leakage.

The score is shown as metres cubed of air lost, per hour, per metre square of building envelope (Floor area, walls area & roof area).

Do I Need an Air Tightness Test?

Under Building Regulations Approved Document L, you will require an air tightness test if you are:

Building any new build residential dwelling(s)

Building any new build commercial space(s)

Air tightness tests are not required on:

Conversion projects

Existing dwellings


We would however, advise anyone doing any building works, or indeed anyone who owns a house or flat to have an air tightness test. We can point out areas of air leakage, which when sealed can dramatically lower your heating bills, saving you money in the long run.

Written by

Robert & Adam Joselyn

Robert & Adam Joselyn are proud of having grown from a small, family-owned firm to one of the fastest growing building regulations testing specialists in the UK. They deliver testing to the highest standard, whilst offering the best commercial value.

What is an Air Tightness Test?

Offered By

RJ Acoustics

177 Balmoral Drive
Borehamwood, Hertfordshire WD6 2QD