In this article, you’ll learn what Part O of the Building Regulations is, in regards to overheating, the requirements necessary to comply, and our thoughts on which route to take.

Insulation and draught proofing are the attention-grabbing headlines of sustainable building practices to help keep buildings warm in winter. However, as the effects of climate change become more apartment with warmer summers and more frequent heatwaves, ensuring the homes are designed and built to prevent overheating is becoming more important.

Dwellings are also being more commonly built with lightweight materials such as timber frames, that lack thermal mass. This can further contribute to overheating in a dwelling.

Part O of the Building Regulations

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Part O of the Building Regulations 2010 (that took effect in June 2022) is concerned with the risk of overheating in new dwellings. It requires that buildings are designed and constructed to reduce the amount of solar gain in summer and to provide adequate means of removing heat from the indoor environment.

Overheating is a serious problem in the UK, and according to the English House Survey 2020-21, some 1.9 million households are experiencing it. A report by the Climate Change Committee has also expressed that this can lead to a number of health problems, including heatstroke, dehydration, and respiratory problems. It can also make it difficult to sleep and concentrate which is especially pertinent with more people working from home.

How do you calculate the risk of overheating?

Building Regulations Part O set out a number of requirements for new dwellings to reduce the risk of overheating with an Overheating Calculation Assessment. These include but are not limited to:

The Building Regulations also provide guidance on how to assess the risk of overheating in a particular dwelling. This assessment should take into account the location of the dwelling, the orientation of the dwelling, the type of glazing, and the amount of shading.

Approved document Part O 2021 mandates that rooms in a dwelling are evaluated in isolation instead of the previously used dwelling average and it provides two methods for assessing overheating risk in dwellings:

  1. The Simplified Route
  2. The Dynamic Thermal Modelling Route

The Simplified Route

The Simplified method can be used for moderate and high risk areas for overheating, in dwellings with or without cross ventilation. It is more suited for dwellings located outside of large cities and for traditional housing types. The simplified method is focused on design criteria including maximum glazed areas & minimum free areas of openings. The simplified method requires no modelling but requires detailed measurements and window design.

The Dynamic Thermal Modelling Route

The Dynamic thermal modelling route involves much more detail than the simplified method and involves modelling the dwelling in an approved dynamic simulation modelling tool such as DesignBuilder. Dynamic thermal modelling uses comfort-based criteria based on CIBSE TM59. It provides more design flexibility and needs to be used if nighttime noise limits, pollution or a risk of failing prevents openings from being used for natural ventilation. It also needs to be used for schemes which have long corridors or long hot water pipes and for developments within large cities, especially in London.

Is overheating compliance mandatory in the UK?

Yes. Part O of the Building Regulations states that reasonable provision must be made in respect of a dwelling containing one or more rooms for residential purposes to limit unwanted solar gains in summer, and provide an adequate means to remove heat from the indoor environment.

House builders must demonstrate to building control bodies that they have complied with the overheating requirements of Part O. This can be done by submitting an Overheating Assessment, which is a report that outlines the steps that have been taken to reduce the risk of overheating in the building.

Failure to comply with the overheating requirements of Part O can result in a number of penalties, including fines and enforcement notices.

Energy expert thoughts

Both the simplified route and dynamic thermal modelling route have a set of criteria that must be considered and reviewed. This ensures that the right assessment route is selected to show compliance.

The criteria include considering night-time noise, security for openings in ground floor bedrooms and easily accessible bedrooms, safety, protection from falling (Part K), and pollution. If after reviewing these criteria natural ventilation cannot be relied on for heat dissipation, due to noise, security, pollution, or safety then the dynamic route needs to be taken.

To find out more about Part O of the Building Regulations you can read the Part O 2021 (England) Technical Guidance. Alternatively, our team are experienced in providing overheating assessments using the simplified methodology and dynamic thermal modelling method. 

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