Part O Overheating Calculations

Building Regulations Part O is designed to prevent excessive indoor temperatures in residential buildings, ensuring occupant comfort and safety. Compliance can be demonstrated using either the Simplified Method or Dynamic Simulation Modelling (DSM), each with distinct approaches and suitability for different projects.

What is Part O

What is Part O of the Building Regulations?

Part O of the Building Regulations was introduced in June 2022 to address the risk of overheating in residential buildings. It applies to new dwellings, care homes, and student accommodations in England and aims to ensure indoor temperatures remain at comfortable and safe levels during hot weather.

Why Was Part O Introduced?

With rising global temperatures and increasing urban density, overheating in homes has become a growing concern. Poorly ventilated and highly glazed buildings, particularly in cities, can trap heat, leading to discomfort, health risks, and even fatalities in extreme cases. Part O sets out requirements to mitigate these risks.

Compliance can be demonstrated using either the Simplified Method or Dynamic Simulation Modelling (DSM), each with distinct approaches and suitability for different projects.

Simplified vs. DSM Methods

Simplified Method – Prescriptive & Easy to Apply

This method uses a set of fixed criteria based on glazing areas, window opening sizes, shading, and cross-ventilation. If a design meets these limits, it passes. While straightforward and quick to apply, it can be restrictive—particularly in urban settings with high external temperatures or limited natural ventilation.
Dynamic Simulation Modelling (DSM) – Detailed & Flexible

DSM is a computer-based thermal analysis that models a building’s response to real-world conditions, including solar gains, ventilation rates, occupancy patterns, and external weather data. This method allows for greater design flexibility and can demonstrate compliance even when the Simplified Method fails.
Which Method to Use?
- The Simplified Method is best suited for low-risk developments with standard design features and good ventilation.
- DSM is recommended for complex designs, high-density urban areas, or buildings with extensive glazing, as it provides a more accurate assessment of overheating risk.