Part O – Overheating 

Building Compliance Testing Limited can provide you with a fast and cost effective Overheating Calculations and Modelling to demonstrate compliance with Part O of the Building Regulations.

Overheating Assessment and TM59 Modelling

The aim of requirement O1 is to protect the health and welfare of occupants of the building by
reducing the occurrence of high indoor temperatures. In the Secretary of State’s view, requirement O1 is met by designing and constructing the building to achieve both of the following.

a. Limiting unwanted solar gains in summer.
b. Providing an adequate means of removing excess heat from the indoor environment.

The guidance and regulations are written for the purposes of protecting health and welfare and does not guarantee the comfort of building occupants.


In the Secretary of State’s view, compliance with requirement O1 can be demonstrated by using one of the following methods.
a. The simplified method for limiting solar gains and providing a means of removing excess heat
b. The dynamic thermal modelling method


What is Part O?

The goal of Part O is to limit solar gains within summer and provide adequate means of quickly removing excess heat from indoor environments through ventilation.

At Building Compliance Testing we encourage the design and construction of buildings that limit excessive solar gains to ensure compliance with Part O and ensure the end-users have guaranteed comfort and health

Here at Building Compliance Testing we can demonstrate Part O Overheating compliance through Simplified Method Assessment and TM59 Dynamic Thermal Modelling.

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Simplified Method Overheating Assessment

The simplified method for overheating assessment (as outlined in Part O of the Building Regulations) focuses on limiting solar gains and removing excess heat in new residential buildings. It considers factors such as glazing area in proportion to floor space and prescribes minimum free areas for ventilation openings. However, it’s not suitable for buildings with large amounts of glazing, bespoke ventilation systems, communal heating systems or significant horizontal pipework.


TM59 Compliant Dynamic Thermal Modelling Method

In contrast, dynamic thermal modelling (DTM) uses specialised software to model heat transfer within a building, considering factors like solar shading, thermal mass, and occupant behaviour. DTM provides a more accurate assessment, allowing for tailored solutions beyond prescribed limits, however is more costly and time consuming.

An Interdisciplinary Approach

At Building Compliance Testing we not only acknowledge risks of overheating but too take into account air quality, acoustics and ventilation. We specialise in:

    • Part F Ventilation – ensuring an adequate ventilation strategy is designed and implemented to ensure overall compliance.
    • BS8233 and BS4142 Environmental Noise Assessments – In locations where external noise maybe an issue the overheating mitigation strategy should take account of the likelihood of the windows being closed during sleeping hours. Noisy is defined as 40dB LAeq,T over 8 hours ‘2300-0700’ & 55dB LAFmax, more than 10 times a night. It maybe required to have a noise assessment performed to demonstrate these values are not exceeded.
    • Air Quality Assessments – Dwellings near significant local pollution should follow Approved document Part F to reduce the intake of pollutants.
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