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Overheating – Simplified Method or CIBSE TM59 Assessments
Approved Document O of the Building Regulations allows for two methods of determining the overheating risk in new dwellings, namely the Simplified Method and the Dynamic Simulation Model, commonly known as CIBSE TM59 assessments.
Simplified Overheating Method
The simplified method is a quick, cost-effective approach to achieving Part O Building Regulations compliance. It is suitable for straightforward developments and operates by adhering to a set of prescribed design limits and criteria. These criteria include restrictions on glazing, minimum ventilation levels, and solar shading requirements based on the building’s location, orientation, and window size. If the design remains within these established limits, it is assumed to satisfy the overheating risk assessment requirements. While this method is efficient and economical, it may not be appropriate for all projects, particularly in dense urban areas or high-risk designs.
For more complex designs or situations where limits cannot be met, a dynamic simulation model is required.
Dynamic Simulation Model - CIBSE TM59 Assessment
The dynamic simulation method, often referred to as TM59, offers a detailed approach for conducting an overheating risk assessment in residential buildings. This involves creating a thermal model to simulate a building's performance over time. Utilising specialised software, the model considers factors such as CIBSE weather data, solar gains, occupancy patterns, internal heat gains, ventilation, and building materials. It predicts hourly internal temperatures, typically over a year, to identify periods when overheating may occur. The results are evaluated against the comfort criteria defined in the CIBSE TM59 methodology. If these thresholds are exceeded, mitigation measures such as enhancing shading, increasing ventilation, or reducing solar gain are necessary until acceptable conditions are reached. This method provides a more accurate and robust assessment, ensuring that dwellings are designed to remain comfortable, even during extended periods of hot weather.
From simplified analysis to dynamic simulation modelling, Energy Planning & Compliance Solutions offers tailored support for developments across the UK, ensuring they are compliant, efficient, and future-ready. To discuss your Part O compliance further, please call 01484 627535, email info@energyplanningcompliance.co.uk or complete the enquiry form below.
How can Energy Planning & Compliance Solutions Assist?
- Experienced consultancy providing practical solutions
- Advice and recommendations for appropriate mitigation measures, where necessary
- Support from early design stages through to Building Control sign-off
- Nationwide coverage
- Competitive pricing and fast turnaround times
The Overheating Assessment Process Explained
Provide your planning drawings and specifications. A detailed review of these will determine whether the simplified method or the Dynamic Simulation Modelling approach would be best suited to your project’s needs in achieving Building Regulations compliance. For the majority of smaller projects, the more affordable simplified method should be sufficient, but where compliance cannot be achieved using this method, a CIBSE TM59 assessment may be more appropriate.
Glazing ratios, façade design, and ventilation strategies, along with other key inputs such as occupancy profiles, equipment loads, and local weather data, are incorporated into a dynamic simulation model. Simulations are then conducted to evaluate temperature performance across representative spaces and orientations. If an overheating risk assessment identifies potential issues, clear and proportionate recommendations in accordance with the cooling hierarchy are provided. These may include adjustments to shading, glazing specification, ventilation design, or façade configuration.
Reports are structured for submission to Building Control or planning authorities and clearly demonstrate compliance with Part O and TM59 as required.
