What is an air test and when is one required?

So what is an air test? An air test is the assessment of the total leakage from a building at a set reference pressure of 50 pascals (Pa).

This is achieved through two different types of equipment: a 50Pa fan system, or a 4Pa low-pressure pulse system. Both types of equipment have pros and cons, with most air testers preferring the more tried-and-tested 50Pa ‘blower door’ system due to faster turnaround and track record.

As air tightness is part of building control sign-off, a competent professional must undertake an air test following CIBSE TM23 regulations for any buildings approved after June 2022, and ATTMA TSL1 guidelines for earlier builds. Generally, the building must have all external penetrations finished and installed, and be in its finished format:
• all exterior doors and windows in position, and
• any gas, water or electrical lines/pipework signed off.

What happens during an air test?

The air tester will set up the testing equipment and undertake numerous readings (a minimum of seven) at different reference pressures both above and below the target 50Pa value. This is used to chart a graph from which the reference 50Pa reading is taken – multiple test points give a more accurate final result.

This air leakage result is then compared with a set of building calculations detailing either the total building envelope (all external walls, floors, and ceilings) for Building Regulations or with the total air volume within the building for certain international standards, such as Passivhaus. Click here to find out more about these elements.

Here’s a condensed list of non-dwelling buildings that don’t require an air test:

• Buildings with a floor area of less than 500m2.
• If not tested, then a default value of 15 m3/(h.m2) at 50 Pa must be used.
• Factory modular buildings – can use installer-provided air testing data + 1.0 m3/(h.m2) if:
  Under 500m2
• Planned service life of over two years but mobile (not static in a single location for more than two years).
• No site assembly is required other than linking via standard details.
• Large extensions.
• If building control agrees that it would be impractical to seal off, then it would be treated as a ‘large/complex building’.
• Large/complex building.
• Detailed justification of why air testing is impractical.
• Detailed strategy on how continuous air barrier will be achieved.
• Requires expert advice – no better than 5 m3/(h.m2) at 50Pa can be claimed.
• Compartmentalised Buildings.
• If the building is made of self-contained units with no internal connections, then a reference test on a representative area can be used.
• If fails, then multiple tests will be needed to confirm that all areas achieve the expected standard.

When is an air test required?

With the push for Net Zero and improving UK housing stock, from June 2022 air tightness testing became a requirement in all new-build dwellings, and most commercial/non-dwellings. Whenever a new Energy Performance Certificate (EPC) is compiled, this follows a process document called a Standard Assessment Procedure (SAP).

To create an EPC, the SAP compiles a wide range of different data, from floor areas, glazing types, insulation values and wall orientations to estimate the amount of heating, energy efficiency and any additional elements that may need to be considered. One key component of this input data is the designed air permeability of the building, which is an estimation of the air leakage in a structure.

Alongside the improvements to minimum specifications for insulation and glazing levels in buildings – it would be difficult to build a home with single glazing and no insulation – the same applies to air tightness, with an increasing focus on making buildings less draughty and therefore more energy efficient.

So, what is air tightness?

We’ve mentioned air tightness multiple times above, but what is it and how can you improve the air tightness of your future build? This blog explains all.