Find out how the new AD L will impact your upcoming developments AD L White Paper

Part L: Will single plots need air testing?

25 Nov 2019


In this series of articles, we aim to answer some of your questions about the upcoming changes to Approved Documents L and F, SAP methodology and the Future Homes Standard.

Current proposals suggest these regulations will be coming into force in England from October 2020. Contact us with your own questions about the regulation changes, or to discuss our training seminars and workshops.


I have a single plot development. Will I need to have it air tested?

Yes. The current air test exemption rule for sites with a single dwelling is being removed.

If you are constructing a single dwelling under current building regulations you have the option to seek an exemption from having that dwelling air tested.

This approach can only be taken if you can prove the dwelling will meet the Target Emission Rate (and the Target Fabric Energy Efficiency in England) if it is based on an assumed air test result of 15.

For a building to comply with current targets the maximum air test result allowed is 10. This means the default is 50% worse than the acceptable threshold which will lead to poor performance in the SAP model and will also impact the Energy Performance Certificate rating of the dwelling.

It’s quite a challenge to achieve AD L compliance with a default 15 air test value. You need to invest heavily in the building fabric by adopting very low U-Values, significantly reducing heat loss through thermal bridging and installing triple glazing. And usually that’s still not enough.

Developers who consider taking this route find it is cheaper and more convenient to have the air test completed in most cases.

So why have the exemption if it can be used so rarely?

It’s a hangover from earlier versions of AD L when it was easier to meet the mandatory targets. A builder could opt to use a default air test value and could still reach compliance by improving the specification of the dwelling.

We are now working to such tough targets that attempting to use an air test default at 15 is rarely viable, and as we prepare to switch to AD L 2020 this air test exemption will no longer be relevant, so is being removed from the Approved Document entirely.

If the proposed changes to AD L are carried through into building regulations, then every new dwelling built from next year will need to be air tested. No exemptions for single plot developments, no sample testing and no confidence factor calculations.

The maximum air test score is being lowered from 10 to 8, but we expect tests will need to exceed this to ensure the new Target Emission and Primary Energy Rates are met.

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