What is an air test pass or fail?

Ensuring a successful air test requires a thorough understanding of building regulations and their impact. With the recent updates in 2021 and the impending Future Homes Standard in 2025, every new construction project is mandated to undergo air tightness testing. As a construction professional, comprehending the significance of air test results can mean the difference between timely project completion and anxiety-inducing test days. 

Passing air tests is integral to obtaining project approvals. Therefore, grasping the fundamentals of the process, including its mechanics, the activities on the test day, and the trades involved, is crucial – have a read of our previous blog, What is an air test?, to find out more. 

The air test value specified in building regulations remains uncertain until the as-built stage, making it a final unknown in the building process. This discrepancy between the ‘designed’ and ‘as-built’ air permeability scores underscores the complexity of achieving the desired outcome. Striking the right balance is key, as being excessively airtight or leaky both pose challenges. 

Despite the absence of a fixed threshold, there exists a minimum level of air permeability allowed by current regulations — 8m3/h.m2 (AP50). Falling below this score results in a failed test at sign-off, emphasising the importance of meticulous planning and execution. 

The key for deciding what is a pass or fail for your air test, is determined by two principal factors:

Building Design – Ventilation and Airtightness 

New builds must now explain how they are designed to ensure the internal environment remains fresh and healthy – this is all explained in the new Part F building regulations, and are scored accordingly.  

These range from lower scoring ‘uncontrolled systems’ such as trickle vents right through to high-scoring smart-tech systems which recover waste heat and circulate fresh air to some or all the rooms. 

By following the adage “build tight, ventilate right”, the higher-scoring/better the active ventilation, such as MEV or MVHR, the less draughty and, therefore, more energy efficient the building can be – all helping to boost project value and achieve compliance. With active ventilation, you can never seal a building too airtight – taking one unknown element out of the equation! 

EPCs and Building Performance – Project Value 

Building Regs require the designed air permeability to be a minimum of 5m3/h.m2 (AP50)– but allow you to choose any number smaller than this, right down to ultra-low-energy homes (Passivhaus and better). By setting your ambitions higher, the SAP calculator rewards the project – more airtight = higher EPC! 

For example, in our 200m2 project with standard ventilation and airtightness, the Dwelling would achieve an EPC rating of C.  

However, when the draughts are reduced and airtightness score improved to hit best-in-class (see case study), the project gained an additional 6 SAP points – or over half a full EPC grade! To achieve the same boost, you would have to install a 2 kW (6-8 Panel) Solar Panel Array and a 4 kWh battery pack – a significant cost for any project! 

In conclusion, there’s no one-size-fits-all approach to air test success – it all depends on the design of the building. It’s essential to align ventilation and airtightness strategies with project goals and regulatory requirements – remembering the catchphrase “build tight, ventilate right” helps to ensure the building adheres to best practices and mitigates the risk of air test failures. 

Airtightness is now a key item to consider throughout the build process – and with technologies like AeroBarrier, you can guarantee no air test fails on any of your projects.