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Air Pressure Test Certificate

An Air Pressure Test Certificate (also called an Air Tightness Test) records the measured air permeability of a building envelope. Required for Part L compliance on new builds and extensions, the test is carried out by an ATTMA or EAS registered tester using a blower door.

Building Regulations Part L, ATTMA TSL1/TSL2Valid: One-off (at completion)

What it covers

  • Building measurements (floor area, envelope area, volume)
  • Test method and equipment details
  • Air permeability result at 50 Pa
  • Pass/fail against Part L target
  • Wind conditions and temperature correction

Who needs a Air Tightness Test?

New build developers
Self-builders
Building Control

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Frequently asked questions about Air Tightness Test

Is an air tightness test mandatory?
For new dwellings and non-domestic buildings, yes — unless the SAP calculation uses a worst-case default of 15 m³/(h·m²), which makes it very hard to meet overall energy targets. In practice, almost all new builds are tested.
What is the pass threshold?
For new dwellings under Part L1A, the maximum air permeability is 10 m³/(h·m²) at 50 Pa. Most designs target 3-5 m³/(h·m²) to meet overall energy requirements.

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