Signed Off
List your firm Get quotes
02 · Building Regulations · Part L

Air tightness testing

An air tightness test measures how much air leaks out of a building through gaps in its fabric. Under the 2021 Approved Document L, every new home in England should be tested, and the result feeds into the as-built SAP calculation.

DWGuide by Dan Wallis · Updated 27 September 2026

This guide covers the rules in England. See Wales, Scotland and Northern Ireland.

233 air tightness testersPart L
Who needs oneAnyone building a new home
Who can do itA tester registered with a recognised scheme such as ATTMA or iATS
WhenWhen the building envelope is complete, before the as-built SAP

233 air tightness testers listed across the UK

Featured (paid) listings first, then A–Z · How we check listings

Find air tightness testers by region

London (26) South East (43) East of England (38) South West (35) West Midlands (23) East Midlands (16) Yorkshire and the Humber (15) North West (12) North East (3) Wales (4) Scotland (22) Northern Ireland (17)

National providers (48)

Regional providers (check they cover your area) (1)

What the test involves

The tester seals vents and extract fans, then either uses a fan in a doorway to pressurise the home (a blower door test) or releases a short pulse of air (the pulse test). Both methods are accepted for new homes under Part L.

The result is given in m³/(h·m²) at 50 pascals. The limit for a new home is 8.0, but your SAP calculation will almost always assume a much better figure, and that design figure is what you need to achieve.

How to avoid a failed test

  • Agree the target figure with your SAP assessor early, and tell your builder
  • Seal service penetrations, loft hatches and window and door frames carefully
  • Book a pre-test or a diagnostic test on larger projects so problems can be fixed before plastering
  • Make sure the home is finished enough to test: doors, windows and sealed services in place

In Wales, Scotland and Northern Ireland

This guide describes the rules in England. Building regulations are devolved, so here is how air tightness testing works in the rest of the UK.

Wales

Every new home is tested, with the same limit of 8.0 m³/(h·m²) at 50 Pa, and pulse tests are accepted. The limit stays the same under the new Welsh rules from March 2027.

Scotland

Every new home has been tested since February 2023, with no sampling. There is no fixed pass mark like England’s 8.0: guidance recommends designing to 7 m³/(h·m²) or better, and a higher figure must be justified to building standards. Blower door and pulse tests are both accepted.

Northern Ireland

Not every home is tested. On each development, a sample of each house type is tested (three of each type, or half of them), and untested homes take the average result plus a margin. The limit is 10 m³/(h·m²), and results go to the council within 5 days. Check with the council before booking a pulse test.

Common questions

Does my extension need an air test?

Not normally. Air testing is required for new homes, and your building control body will tell you if anything else needs one.

What happens if the home fails?

The leaks are found and sealed, then the home is retested. Many testers offer a diagnostic smoke test to find the problem areas.

Is the pulse test allowed?

Yes. The low-pressure pulse method and the fan pressurisation method are both accepted for new homes under the 2021 Part L.

What is the pass mark?

The limit for a new home in England is 8.0 m³/(h·m²) at 50 pascals. Your SAP calculation will almost always assume a better figure, and that design figure is the one you need to achieve.

When should I book the test?

When the building envelope is complete, with doors, windows and sealed services in place, and before the as-built SAP. On larger projects a pre-test or diagnostic test helps find problems before plastering.

New to the jargon? See our glossary of terms, from air permeability to TrustMark.