Why is it so hard to guarantee an air test result?

Airtightness is influenced by a combination of factors, including the care and attention given during the build process, the design, detailing, and even the initial shape of the building. Consequently, predicting a building’s airtightness with precision is traditionally very challenging. This difficulty is why Building Regulations in the UK now require a ‘completion’ air test for every new build home. Even within a specific set of house types, each final air test can yield different results.

While you can standardise build specifications such as U-values, window choices, and wall constructions across similar house types, achieving airtightness is not straightforward. Any penetrations through walls, floors, or ceilings, such as cabling or pipework, can create leakage areas, impacting the final air test results.
Building Regulations acknowledge this variability: although an architect is required to design a continuous and robust airtightness layer, actual completion often reveals discrepancies. Even the stringent Passivhaus standard allows for some unintentional leakage, highlighting the gap between design and reality.

Traditional airtightness solutions like tapes, sheet materials, and manually applied liquids can effectively address known leakage areas. However, these methods fall short because measuring their impact on the building’s overall airtightness is difficult—often referred to as the ‘tape and pray’ approach.

Furthermore, the only time airtightness is typically checked is with the final sign-off air test, just before handover. At this point, most surfaces and fixtures are completed, making it challenging to address hidden leakage points adequately. As a result, testers can often only treat symptoms rather than underlying issues.

Incorporating airtightness strategies from the outset of your project is crucial for ensuring compliance and avoiding costly delays. By using technologies like AeroBarrier and adhering to best practices in design and construction, you can minimise the risk of project failure and ensure on-time completions and handovers.