Air Tightness Testing Terminology

When it comes to air tightness testing, there can be excessive amount of terminology used to describe a fairly simple type of test. To try and help our clients better understand this terminology we have collated a list and description of the most common terms:

Air test, Air tightness Test, Air Leakage Test or Air Pressure Test

The development is pressure tested by setting up blower door testing equipment and measuring the airflow rates required to keep the building at various positive pressures – usually 25-70 Pa.

Air leakage Paths

Air leakage paths defined as areas where the building envelope has not been adequately finished and sealed resulting in excess amount of air leakage.

Air barrier or Air Seal Line

The air barrier or air seal line is the physical components that make up the airtight envelope of the building. The air barrier/air seal line needs to be continuous around the whole inner envelope, including the roof, walls and ground floors and windows and doors.

Air Permeability Rate

This is expressed as the amount of air leakage in cubic metres, per hour, per square metre of envelope or also shown as m3/hr/m2 at a nominal pressure differential of 50 Pascals, between inside and outside the building envelope. The usual air permeability rate is usually shown in the design stage SAP report and most buildings now need to achieve a figure of 5m3/hr/m2.

Smoke Test

This is undertaken if the Building fails the air tightness testing to highlight areas of air leakage so targeted remedial sealing works can be undertaken. There are two types of smoke test a large scale commercial smoke test using a large smoke generator and a smaller ‘smoke puffer ’ test which is mostly used on smaller residential buildings.


this is the air flow rate required to pressurise the building envelope to 50 Pascals, the measured unit of which is cubic metres per second.

Temporarily Sealing

Temporally sealing can be undertaken to various areas within the building and is allowed in Building Regulations Part L. The usual areas that are ok to seal are trickle vents to windows and doors, fireplaces, air bricks and extract vents within kitchens, utility rooms, bathrooms and toilets.

Potential Building Performance Issues

Existing building envelope performance issues are often brought to light by occupants complaining of the buildings/rooms being too cold or draughty. The buildings are often too cold in winter or too hot in summer. These complaints are often difficult to diagnose and very difficult to remedy.

Air Pressure Testing can employ various techniques, such as air tightness testing, smoke tests, thermal imaging surveys and visual site surveys to make a diagnosis of the building performance issues. Once we have undertaken the chosen diagnosis technique, we can recommend the remedial solutions to the client so targeted remedial sealing works can be undertaken and thereafter a final air tightness test to check the air permeability rate has been lowered to acceptable levels.

If you require air tightness testing on a new or existing building then please don’t hesitate to contact us on or call Darren direct on 07775623464