In this blog, we’ll cover everything you need to know about the Part O Building regulations:

Part O Building Regulations: The Problem of Overheating

Overheating is a serious problem in the UK, with some 1.9 million households are experiencing it (English House Survey 2020-21).

While insulation and draught proofing remain important for sustainable building practices to help keep buildings warm in winter, the focus needs to shift towards summer comfort as well. Due to the effects of climate change become more apparent with warmer summers and more frequent heatwaves, ensuring that homes are designed and built to prevent overheating is becoming more important.

To address this growing concern, the Part O Building Regulations mandate that new homes are designed and built to prevent overheating, especially since new dwellings are increasingly built with lightweight materials such as timber frames, that lack thermal mass.

A report by the Climate Change Committee highlights the health risks of overheating, including heatstroke, dehydration, and respiratory problems. It can also disrupt sleep and concentration, a significant concern for the growing number of people working from home.

The Part O Building Regulations

Part O Building Regulations: HM Government, The Building Regulations 2010, Overheating Approved Document O, 2021 Edition
Click to view online

The Part O Building Regulations (introduced in 2010 and updated June 2022) focus on the the risk of overheating in new dwellings. These regulations aim to ensure comfortable living spaces year-round and prevent overheating by addressing the issues of excessive heat gain during summer months. They require 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.

The Part O Regulations set out a number of requirements for new dwellings to reduce the risk of overheating. These include but are not limited to:

  • Limiting the amount of solar gain in summer:
    Using shading like awnings or trees, or glazing with a low solar gain coefficient.
  • Providing adequate ventilation:
    Natural ventilation through windows or by mechanical ventilation.
  • Using thermal insulation: 
    Helping keep the heat out in summer.
  • Installing cooling systems: 
    Only be used as a last resort – they can be expensive to run.

How to Assess Overheating Risk

The Building Regulations provide guidance for assessing overheating risk in a particular dwelling. This overheating calculation assessment takes into account factors like 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 evaluating rooms individually, 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 is suitable for moderate and high overheating risk areas, with or without cross ventilation. This method is ideal for dwellings located outside of large cities and for traditional housing types. It focuses on design criteria like maximum glazed window areas & minimum ventilation openings. While no modelling is required, detailed measurements and window design are crucial.

Benefits: Quicker and easier to implement for simpler projects.

The Dynamic Thermal Modelling Route

This more detailed approach involves modelling the dwelling in an approved software tool, like DesignBuilder. It uses comfort-based criteria based on CIBSE TM59 and offers greater design flexibility. This route is necessary when:

Benefits: More flexibility for complex designs and challenging solutions.

Is Overheating Compliance Mandatory in the UK?

Yes, absolutely. Part O of the Building Regulations mandates that new dwellings, containing one or more rooms for residential purposes, have provisions to:

This ensures comfortable and healthy living spaces year-round. Anyone constructing a new dwelling must demonstrate compliance with these overheating requirements to building control bodies. This is typically done by submitting an Overheating Assessment report detailing the steps taken to mitigate overheating risk in the building. Failure to comply can result in penalties such as fines and enforcement notices.

Choosing the Right Assessment Route

Both the Simplified and Dynamic Thermal Modelling routes have specific criteria to ensure selecting the right approach for compliance. These criteria primarily focus on:

Achieving Compliance with Part O Building Regulations

By following the Part O guidelines and ensuring compliance you can not only avoid fines but also create a cool and sustainable home for the future.

To find out more about the regulations you can read Part O 2021 (England) Technical Guidance. Our team are experienced in providing overheating assessments using both the simplified methodology and dynamic thermal modelling method – get in touch today for a free consultation to discuss your specific project requirements.

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