Overheating Assessments

Simplified Method or CIBSE TM59?

The Simplified Overheating Assessments offer a quick, policy compliant method to identify overheating risks early in the design phase. 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.

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.