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  • Seb Kouyoumjian

What a Scorcher! The New Insulation (and Overheating) Regulations

As Britain has its moment (in the core) of the sun - Tyler Parkes HQ is experiencing 40°C as we write - there is no better time to list the recent changes and improvements to the Building Regulations ‘Approved Documents’* covering overheating and insulation. In this article, we’ll be referring specifically to those regulations applicable to new and extended/renovated houses in England, updated in mid-June 2022.

Approved Document L, Including Thermal Insulation

In the footnotes, we've listed the new U-values (a measure of how much heat escapes a wall, floor, roof etc.) a housing project should achieve. Bear in mind, these are a minimum standard, and it is possible to get even lower U-values with current technology, which will bring your energy bills down.

You'll be seeing a lot more solar panels

If you don't understand U-values, in short, the insulation requirements for both new houses and extensions and renovations have been tightened. So more insulation than usual will be required to walls, roofs, and floors, and windows will need to be higher performing. The days of meeting the regulations with mineral wool in cavity walls are very much over (unless the wall is lined with a very thick layer of additional insulation on the inside).

The End of Gas?

Installing gas boilers or electric panel heaters will, generally, make it hard to pass the updated Building Regulations. The regulatory update signals a shift to renewables, meaning a pass will usually require some combination of heat recovery (e.g. of waste water), air- or ground-source heat pumps, and so on. Applicants will continue to have to provide a SAP** calculation to show how the whole building performs in terms of energy loss (e.g. insulation) and energy use (e.g. heating plant).

Will All New Houses Need Triple Glazing?

In practice, the new targets for windows may require new houses to have triple-glazed windows and doors. This may be offset by a small provision of PV panels. Again it all depends on the SAP calculations for the building in question.

Approved Document O, Dealing with Overheating

This is a completely new concept for the Building Regulations (though not at all new compared to standards like Passive House, BREEAM, etc.). Applicants will need to prove their proposals will not overheat (though the Approved Document acknowledges what is considered ‘too hot’ is subjective).

Here are a few ways to comply with the rules for dwellings:

  • Do not exceed 'maximum permitted glazing areas', i.e. each external wall should not have more than a certain percentage of glazing

  • Provide cross-ventilation, meaning openable windows on opposite sides of a dwelling

  • Provide solar shading, especially in areas like London and Manchester (which are at higher risk of overheating - but Birmingham is 'medium risk'), to reduce unwanted heat from the sun getting into a building

Approved Document O will have a massive impact on design at the planning stage, as compliance will often involve the use of brise-soleils, the placing of balconies to shade windows beneath them, the use of external blinds and overhangs, and the consideration of the size and orientation of windows.

And What’s Missing?

We are pleased to see the changes as a move in the right direction – we all want more comfortable and cheaper to run homes. However, we think the construction industry needs far more guidance on not just sustainability in running a building, but also while building it, e.g. by using fewer high-carbon petrochemical-based insulating products (e.g. Kingspan, Celotex, Recticel).

For overheating, guidance is needed on how to reduce overheating through the use of sustainable materials with a low ‘decrement factor’. These are materials with properties which reduce the speed with which solar heat gets through a building’s fabric – for example stone walls and wood fibre insulation reduce overheating better than brick walls and PIR insulation.

Coming Soon…

The Future Homes Standard (FHS) is planned for 2025. This will require new homes to not be reliant on fossil fuels for heating and hot water. So we’re expecting more homes to be better insulated and fitted with smart technology to recapture waste heat.

An Important Note

The information above is intended as a guide to the changes, and should not be used as a substitute for checking the full suite of Approved Documents. If you would like to discuss how these regulations affect your project, please call Seb Kouyoumjian of our Architectural Team on 0121 744 5511 .


Updated U-values for Dwellings

New Build Houses

Element U-Value (W/m2K)

Walls 0.18

Roof 0.11

Floor 0.13

Windows/Doors 1.2 (the whole unit, including frames)***

New Elements in Extensions

Element U-Value (W/m2K)

Walls 0.18

Roof 0.15

Floor 0.18

Windows/Doors 1.4 (the whole unit, including frames)***


* The Approved Documents give guidance for how to meet the Building Regulations – the laws governing the standard of building work. Note that British Standards or other technical specifications can sometimes be used instead of the Approved Documents. It all depends on context.

** Standard Assessment Procedure, a method of modelling the environmental performance of a building.

*** Window manufacturersoften quote the performance of the glass, which in a double-glazed window can let about half as much heat through compared to the frame. So before buying windows or doors, ensure the manufacturer has given you a full calculation for the whole unit, to prove that it complies


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