An air tightness test measures the extent of air leakage in a building. Improving air tightness of a building not only increases the comfort of the occupants, but can also enhance the building’s energy efficiency.

Gaps and cracks in the building that cause air leakage are often difficult to detect. They may be obscured by internal building finishes or external cladding. Thus the only satisfactory way to show that a building fabric is reasonably airtight is to detect and measure leakage paths within the building fabric.

Air tightness testing is central to the revised Part L of the Building Regulations 2006. Under the new regulations developers must test each dwelling type on each development in England and Wales. The size of dwelling sample depends on whether ‘Robust Details’ have been used. New non-dwellings of 500 m2 and more must also be tested.

There a few things to consider regarding air tightness testing:

• The client needs to send our test engineers the drawings of the development and the design air permeability requirements;
• Air tightness testing can normally be undertaken in 30 – 60min;
• Local weather condition may significantly affect the results. Wind speed should be below 3m s-1 and not exceed 6m s-1;
• Test engineers need to know the size of building envelope and requirements prior to coming to the site.

Download site check list here.

Test procedure

Preparing the site to create air-tight environment:
• Open and secure all internal doors;
• Close all windows;
• Switch off all mechanical ventilation systems;
• Seal ventilation grids;
• Close smoke vents;
• Fill all drainage traps;

On-site testing procedure:
• Check weather conditions (wind speed, temperature, barometric pressure);
• Connect a fan (or fans) to an aperture in the building envelope (e.g. door);
• Set up testing equipment;
• Gradually increase the fan speed to maximum of 50-60Pa;
• Gradually decrease the fan speed to around 20Pa;
• Record the air volume flow through the fan (this equals the air leaking through the building envelope);
• Record pressure differences across the building at each fan speed;

We will thereafter analyse the recorded air tightness test data and present the results to the client in a technical report. In the event of test failure we will make every effort to advise the client on site on appropriate mitigation measures.