AD-O Overheating

The first phase of the Future Homes Standard will launch in England later this year. The aim is for new dwellings to use less energy, have lower fuel bills, a lower carbon footprint, and be comfortable to live in.

Over the coming months, we’ll be writing articles to answer your questions about these regulatory changes. This time we’re covering the details of a brand new building regulation:

AD O: Overheating – What do I need to know?

From June 2022, new buildings in England will need to show compliance with AD O – an Approved Document which specifically targets overheating risk.

This is a new addition to the Building Regulation family and builds on foundations laid by urban planning departments who routinely ask for evidence that building designs won’t cause excessive internal temperatures or require extra energy for cooling systems.

AD O applies to all new dwellings, including dwelling-like buildings such as care homes and shared spaces in apartment blocks. It also applies to new homes created through change-of-use, such as a barn conversion.

There are two options available for achieving compliance. One is a quick check for houses at a lower risk of overheating, and the other is a more comprehensive approach for dwellings at a higher risk.

Developers who are working with conventional house designs outside of London and Manchester are more likely to meet compliance using the quick Simplified Method.

The Simplified targets are calculated based on the amount of glazing a dwelling has, and also the amount of openings.

To comply using this route, the targets check that there aren’t too many windows (which would lead to excessive solar gains) and enough openable doors and windows (to allow the free movement of air).

If the design of the dwelling doesn’t comply using the Simplified approach, the size of windows and doors will need to be revised, and in some cases tinted windows or sun blockers may be required.

Alternatively, the Developer can try the second path to compliance – Dynamic Thermal.

This will be more commonly used by developers of heavily glazed dwellings, apartment blocks, or sites in England’s biggest cities.

Dynamic Thermal is more complex than the Simplified approach but checks the overheating risk with greater accuracy and generates a bespoke set of results and recommendations.

Any designer who’s previously used TM59 analysis to meet a planning condition on overheating will be familiar with how the Dynamic Thermal process works.

Real-life weather data is applied to a 3D thermal model of the development to measure the impact of summer temperatures on the building.

To comply, the internal temperature needs to stay below a maximum target.

If the dwelling fails to comply with the Dynamic approach, the designer will need to go back to the drawing board based on the recommendations from the TM59 assessor.

They may need to consider a different ventilation system, better glazing, or changing the building fabric.

Using a cooling system to remedy overheating risk is a last-resort option only; it can only be considered once all other recommendations are ruled out.

This is because cooling systems use energy, so their inclusion goes against the core principles of the Future Homes Standard which is to design more efficient buildings.

As with other requirements that make up this package of new regulations, AD O will apply on new dwellings where the site is registered with Building Control from June 15th 2022.

It will also be required for any new dwellings where construction hasn’t started before June 15th, 2023 – even if the site was registered under the older version of AD L.

We’ve got five months before AD O rolls out onto new developments, but the Technical Team at Energist is ready now!

We can check the design of your upcoming developments to confirm whether they are AD O compliant, using both the Simplified and Dynamic Thermal routes.

If you have any questions about these changes, feel free to contact the Energist team. Otherwise keep an eye out on our ‘Articles’ page where follow-on information will be published.