What Is Airtightness Testing and Why Does Your Building Need It?
Everything you need to know about air permeability testing in the UK — when it's required, how it works, and what the results mean for your building.
What is airtightness testing?
Airtightness testing — also known as air permeability testing or blower door testing — measures how much air leaks through your building envelope. It’s a critical test for understanding building performance and is often required for Building Regulations compliance.
When is it required?
Under Part L of the Building Regulations, airtightness testing is mandatory for:
- All new dwellings (with some sampling exceptions)
- New non-domestic buildings over 500m²
- Extensions over 1,000m²
How does the test work?
We install a calibrated fan in an external doorway and create a pressure difference between inside and outside the building. By measuring the airflow required to maintain this pressure, we can calculate the air permeability rate.
What do the results mean?
Results are expressed in m³/(h.m²) at 50 Pa — the volume of air passing through the building envelope per hour, per square metre of envelope area. Lower numbers mean a more airtight building.
Typical targets:
- Building Regulations: 10 m³/(h.m²) maximum
- Good practice: 5 m³/(h.m²)
- Passivhaus: 0.6 ACH (approximately 0.3-0.4 m³/(h.m²))
Common air leakage paths
During testing, we often identify leakage at:
- Window and door frames
- Service penetrations (pipes, cables)
- Loft hatches
- Suspended timber floors
- Electrical sockets on external walls
Next steps
If you need airtightness testing for a new build, retrofit project, or quality assurance purposes, get in touch. We provide BS EN ISO 9972 compliant testing with certificates issued within 48 hours.