This year marks two decades since air tightness testing first became part of UK regulations, a milestone that reflects how far the industry has come. From its introduction into Part L building regulations in 2002 to its widespread adoption by 2006, testing has changed and adapted into a core component of modern building performance testing.
At Stroma, our team have played a central role throughout this journey, with teams who were part of the industry’s earliest tests still contributing today.
Our new podcast series brings together experts such as Stuart Oakes, Director of Energy Services, and Adam Nazir, Head of Operations, to explore how air testing has matured and what the next 20 years is shaping up to look like.
As the podcast highlights, air testing has been “quite a journey”, shaped by not just technology and regulations but the growing expectations around building quality and efficiency.
Listen to the '20 Years of Air Tightness' podcast
Key Takeaways on 20 Years of Air Tightness Testing
- Testing has progressed from traditional blower door testing: to quicker, low pressure pulse testing, giving teams more choice in how Air Tightness is measured
- Air tightness now needs to work in step with ventilation strategies: under Part L building regulations and Part F to maintain safe, balanced performance
- As standards tighten, the industry is refocused: on how air tightness affects energy use, comfort and overall occupant wellbeing
- Data gathered from large volumes of tests is helping: to shape better building performance testing practices and guiding decision for the next generation of buildings
The Evolution of Air Tightness Testing
Air tightness became a formal requirement through Part L building regulations in 2002. This set an initial performance threshold of 10 m³/m²/hr. At the time, this was considered “ambitious”. However, today, results below 5 m³/m²/hr are common, reflecting improvements in build quality, materials and testing methodologies.
Blower door testing was traditionally the dominant method throughout this period as it provided reliable and repeatable measurements. However, the introduction of Pulse testing now offers alternative ways to measure Air Tightness in occupied homes and sensitive environments, supporting broader building performance testing strategies.
As the Future Homes Standard continues to develop, the regulatory framework will push performance thresholds even lower, placing Air Tightness at the heart of energy efficiency.
From Early Standards to Modern Regulations
Over two decades, expectations have tightened significantly. The original 10 m³/m²/hr limit is no longer seen as acceptable for new homes or commercial buildings.
Regulatory consultations linked to the Future Homes Standard have indicated that far lower Air Tightness rates may soon be implemented, and with greater emphasis on consistent delivery, not just on compliance.
At Stroma, we continue to support industry understanding through guidance and training to ensure that requirements under Part L building regulations are implemented correctly across all sectors.
Improving Test Results Across Two Decades
In our recent podcast, Adam Nazir comments “the majority of buildings now pass first time because testing has become embedded in the build process”. This shift reflects improved detailing, increased contractor awareness and tighter supply chain coordination.
The progress in this industry is clear but with that there are challenges. It is no longer about simply achieving a ‘pass’; it is about designing and constructing buildings that minimise the risk of failure in the first instance.
Common Causes of Air Tightness Test Failures
Despite advancements and improvements in the industry, failures still occur and this is often due to issues that have persisted for years. In our podcast, Adam Nazir explains that while most buildings now pass “passing isn’t really the issue anymore, it’s about guarding against failure”.
Common issues include weak continuity of the air barrier, poor sequencing on site and inadequate understanding of Air Tightness among trades. These challenges highlight why education and early engagement are key to improving industry requirements.
Junction Detailing and Material Interfaces
Common problem areas include junctions around windows, doors, service penetrations, and changes in material type. As highlighted in the podcast, mismatches “between design and on-site reality” remain a recurring cause of failure.
Early-stage design reviews, mock ups, and ongoing site engagement can resolve a lot of these issues before the testing process actually takes place.
How Early Engagement Reduces Defects: Late-Stage Sealing and On-Site Gaps
Late-stage sealing, rushed installations, or trades unaware of the air barrier strategy may all contribute to failure. The real opportunity lies in preventing these issues upstream, not catching them at the test stage. All the above will either directly or indirectly cause cost increases, so they are seriously worth consideration.
At Stroma, we support teams through consultancy, toolbox talks, and design reviews across a range of services:
The above services we provide sit alongside air tightness within a wider building performance testing framework.
Using Data to Improve Building Performance
With thousands of domestic tests carried out each year, at Stroma, our team can spot patterns that individual projects simply can’t reveal. Repeated testing across similar house types and developments highlight where designs perform well and where issues often occur.
As discussed in our recent podcast, this volume of data offers real insight to help clients avoid recurring problems and refine their approach on future plots. Rather than data being a record of past performance, it now becomes a tool for improving building performance testing outcomes across entire developments.
What Large-Scale Domestic Testing Reveals
Patterns are becoming increasingly clear: certain construction types and sealing methods consistently outperform others, especially where detailing has been considered from the outset. This repeatability helps refine approaches to both testing and construction sequencing.
Feeding Insights Back into Design and Procurement
Using test data at the design and procurement stage helps developers make clearer decisions about products, detailing, and construction methods. When common issues are identified early, they can be designed out rather than fixed on site. As discussed in our podcast, feeding insight back into specification leads to fewer failures, better energy performance, and a smoother experience for homeowners.
Design Assumptions and Ventilation Balance
Air Tightness is closely linked to ventilation strategies. in our podcast we highlight how SAP, HEM, and SBEM outputs are influenced by Air Tightness, particularly at very low-test values. Below 2.5 m³/m²/hr systems such as MVHR are often required to maintain air quality, particularly with the introduction of Part O, which focuses on overheating.
A balanced approach, air tightness, ventilation, and thermal performance working together, is essential as we move towards the Future Homes Standard.
The Growing Role of Air Testing in Retrofit Projects
The retrofit market continues to grow, and air tightness testing now plays a key role in assessing existing homes. A common assumption is that older homes and buildings are always “leaky”, but many traditional constructions, such as solid walls and wet plaster, can be far more airtight than expected.
Carrying out retrofit air tightness testing before any upgrades can help to ensure heat pumps are sized correctly and that ventilation strategies match the real performance of the building.
Complementary Services and the Performance Gap
Air tightness testing is now one part of the larger performance verification approach.
Heat Transfer Coefficient (HTC) Measurements
Demand for HTC (Heat Transfer Coefficient) measurements, 3D U-values and mould risk analysis is growing. This is particularly true in retrofit projects. These services validate real-world heat loss, helping to ensure the building performs as designed. Whilst this may add some cost, it does provide huge value.
Reducing Performance Gaps with Integrated Testing
Integrated testing can help to close the gap between design intent and operational performance, reducing running costs, improving comfort and raising asset value. This supports a broader shift from ‘compliance’ to building performance testing as standard.
Final Thoughts on 20 years of Air Tightness Testing
Two decades of innovation has reshaped how we approach air tightness, with technology data and regulation driving continuous improvement. As our podcast concludes, the industry is moving from tick box exercises to a focused mindset on performance assurance.
Why Continuous Testing and Verification Matter
Continuous improvement through testing reduces risk, supports efficient design, improves occupant comfort, and strengthens long-term building performance. All of these are key priorities as we move towards the Future Homes Standard.