Tackling Overheating with New Part O Building Regulation

Tackling Overheating with New Part O Building Regulation

Part O is a brand-new approved document that’s required in building regulations to tackle overheating within dwellings and buildings that can be used for domestic purposes, which covers buildings such as student accommodation and care homes. This is a growing problem as lots of buildings use glass for natural light, but it can cause solar heat gain.

It’s a new building regulation requirement, but any experienced architects and designers will be used to designing in order to counteract solar-heat gain. But it can be an issue and as buildings become more efficient in their design, there’s an increased chance of overheating.

Let’s take a look at it in more detail:

When did Part O come into force?

The new approved document came into action on 15th June 2022, so new developments bound by building regulations must abide by Part O. But if a construction must abide by a building notice, has made plans application, or put an initial notice in place before 15th June 2022 then they will not have to consider these overheating regulations if work starts before 15th June 2023.

However, buildings developments should be aiming to prevent overheating anyway, so any responsible designers will implement this in plans regardless.

Solar gains can be limited by using shutters, external blinds, or overhangs and here at Urban Skies, we use Solar Shading and Brise Soleil and other solutions/products to prevent solar heat gain in an aesthetically pleasing way.


The requirement of the O1 Overheating Mitigation of the Building Regulations asks that dwellings and buildings used for accommodation need to do the following:

  • Limit unwanted solar gains in summer
  • Provide an adequate means to remove heat from the indoor environment

The safety of people that live in these buildings and dwellings must be considered at all times and with any action taken to prevent overheating. This can be demonstrated by:

  • The Simplified Method, as set out within Section 1 of the Approved Document O.
  • The Dynamic Thermal Modelling Method, as set out within Section 2 of the Approved Document O.

What’s the Simplified Method?

A simplified method can be actioned when a development demonstrates if it has cross-ventilation or not and if it has been assessed as moderate or high risk, which covers the following:

  • ‘High Risk’ Locations are parts of central London and some parts of Central Manchester. The Approved Document O provides post codes of areas of high risk within Appendix C.
  • ‘Moderate Risk’ Locations are all the remaining areas in England not considered as ‘High Risk’.

To limit solar overheating, maximum glazing requirements are put in place and constructions in high risk locations must provide shading by:

  • External Shutters with means of ventilation
  • Glazing with a maximum G-Value of 0.4 and a minimum light transmittance of 0.7.
  • Overhangs with 50 degrees altitude cut-off on due south-facing facades only.

Minimum free areas of openings are also required.

Dynamic Thermal Modelling can be used if a designer wants to build outside of a Simplified Method but still be compliant of Part O Building Regulations.

For more information about how the overheating approved document applies to new dwellings where people sleep overnight and what needs to be in place, get in touch with our team and we’d be happy to discuss any design questions.