Air Leakage Testing Explained: 10 Questions Every Developer Should Know
Getting to Grips with Air Leakage
Air leakage testing is a key requirement of Part L of the Building Regulations for most new residential and commercial buildings. While many developers understand that a test is required before completion, there is often confusion about what the test involves, how to prepare for it and what happens if a building fails.
This guide answers the most common questions about air leakage testing, helping developers, architects, contractors and self-builders understand the process and achieve successful results.
1. What is Air Leakage Testing?
Air leakage testing, sometimes known as airtightness testing, air pressure testing or blower door testing, measures how much uncontrolled air escapes through the building envelope.
The purpose of the test is to assess how effectively a building has been sealed against unwanted air movement. Lower levels of air leakage generally contribute to improved energy efficiency, lower heating costs and better building performance.
2. Why is Air Leakage Testing Required?
Part L of the Building Regulations now requires all new residential and commercial buildings to undergo air leakage testing.
The test forms part of the overall energy performance assessment and helps demonstrate compliance with national energy efficiency standards. Without a valid air test result, Building Control sign-off may be delayed.
3. When Should Air Leakage Testing Be Carried Out?
Testing should only be undertaken once all works associated with sealing the building envelope have been completed.
The property does not need to be decorated and floor finishes are not usually required. However, windows, doors, ceilings, service penetrations and other elements affecting airtightness should be fully installed and completed before testing takes place.
4. What Do You Need on the Day of the Test?
A successful test requires some basic site preparation.
Before the engineer arrives, ensure:
Typically, a standard external doorway approximately 2.1m high by 1m wide is sufficient to accommodate the testing equipment.
5. Can Air Leaks Be Temporarily Sealed During Testing?
Industry standards only permit certain openings to be temporarily sealed during the test.
Examples include:
6. What Are the Most Common Causes of Air Leakage?
Many failed tests occur because small gaps and junctions have not been adequately sealed during construction.
Common problem areas include:
Even small unregulated gaps can significantly affect overall building airtightness.
7. How Can You Improve Airtightness Performance?
Good airtightness starts with attention to detail during construction.
Key recommendations include:
Taking these steps early can significantly improve test outcomes and reduce the need for remedial work later in the project.
8. Why is Dot-and-Dab Plasterboard a Critical Area?
One of the most common sources of air leakage is dot-and-dab plasterboard applied directly to blockwork.
Blockwork itself is not airtight, and the cavity created behind plasterboard can allow air to circulate through the building fabric.
To prevent this:
Proper detailing in these areas can make a significant difference to the final test result.
9. What is a Mid-Construction Air Tightness Inspection?
A mid-construction inspection is a visual site assessment carried out before completion.
The inspection identifies potential leakage paths while building elements remain accessible. This allows contractors to address issues before finishes are installed and before the final air test is undertaken.
10. Is a Mid-Construction Inspection Worth It?
In many cases, yes. Identifying airtightness issues during construction is often far more cost-effective than investigating a failed air leakage test at the end of the project.
A mid-construction inspection can:
Need Help with Air Leakage Testing?
MES Building Solutions provides air leakage testing, airtightness advice and mid-construction inspections for residential and commercial developments across the UK. Whether you’re preparing for Building Control sign-off or looking to improve overall building performance, our team can help you achieve compliance with confidence.
