Failed Your Air Tightness Test? Common Causes and How to Fix Them
Few things are more frustrating than reaching the final stages of a project only to discover you’ve failed your air tightness test.
Whether you’re a developer, builder, contractor or homeowner, a failed test can mean delays, additional costs and unexpected remedial work before Building Regulations sign-off can be achieved.
The good news is that most air leakage issues are entirely fixable once they have been identified.
In this guide, we’ll explain the most common reasons buildings fail an air tightness test, where leaks are usually found, and what you can do to improve your chances of passing first time.
What Does A Failed Air Tightness Test Mean?
An air tightness test measures how much uncontrolled air escapes through the building envelope.
The lower the leakage rate, the better the building performs.
If the measured air leakage exceeds the target set within the project’s SAP calculations or energy strategy, the building may fail to meet the requirements of Part L of the Building Regulations.
This can prevent the project from achieving final sign-off until remedial work has been completed and a retest has been carried out.
Learn more about our Air Tightness Testing Services.
The Most Common Reasons Buildings Fail An Air Tightness Test
Poor Sealing Around Windows And Doors
Window and door openings are among the most common sources of air leakage.
Small gaps around frames can have a surprisingly large impact on the final result.
Even where sealants have been applied, incomplete coverage or damaged seals can allow air to pass through.
Service Penetrations Through Walls And Floors
Every pipe, cable, duct and utility connection that passes through the building envelope creates a potential leakage point.
These areas are often overlooked during construction, particularly when multiple trades are working on site.
Without appropriate sealing, air can travel freely through these gaps.
Loft Hatches And Access Panels
Loft access points, riser cupboards and service panels frequently contribute to failed air tightness tests.
If these openings are not properly sealed, they can create significant leakage pathways.
Junctions Between Building Elements
Where walls meet floors, roofs, ceilings and other structural elements, small gaps can develop during construction.
These junctions often account for a substantial proportion of overall air leakage.
Ventilation Components Installed Incorrectly
Background ventilators and mechanical ventilation systems are essential for healthy indoor environments, but poor installation can lead to unintended air leakage.
Achieving the right balance between air tightness and ventilation is critical.
Our Ventilation Compliance Services can help ensure both requirements are met.
How Air Leaks Are Identified
One of the biggest misconceptions about a failed air tightness test is that you’ll simply receive a pass or fail result.
In reality, testing can provide valuable information about where problems exist.
Depending on the project, techniques such as smoke testing, thermal imaging and Ultrasonic Air Leak Detection can be used to pinpoint leakage paths.
This allows targeted remedial work rather than costly trial-and-error repairs.
Can You Retest After Failing?
Yes.
Most projects that fail an air tightness test can be rectified and retested successfully.
Once leakage points have been identified and repaired, a further test can be arranged to verify compliance.
In many cases, the remedial work required is relatively straightforward once the source of the problem has been located.
How To Improve Your Chances Of Passing First Time
The easiest and most cost-effective approach is to think about air tightness throughout the build rather than waiting until completion.
Some practical steps include:
- Clearly identifying the air barrier strategy early in the project.
- Checking service penetrations before finishes are installed.
- Inspecting windows and doors for gaps before handover.
- Ensuring all trades understand the importance of maintaining airtightness.
- Addressing any issues before final testing takes place.
For larger developments, early testing of sample plots can often identify recurring issues before they affect multiple properties.
Why Early Testing Can Save Time And Money
Many failed air tightness tests happen because problems are discovered too late in the construction process.
At that stage, locating and repairing leaks can be more difficult, more disruptive and more expensive.
Early engagement with an experienced testing company allows potential issues to be identified before they become major obstacles to compliance.
This helps keep projects on schedule and reduces the risk of costly delays.
Need Help With A Failed Air Tightness Test?
If your project has failed an air tightness test, don’t panic.
Most issues can be identified and resolved quickly with the right approach.
At AVT UK, we work with developers, contractors, retrofit teams and homeowners across the UK to identify leakage issues, carry out testing and help projects achieve compliance.
Call 0161 706 1401 or get in touch with our team to discuss your project.