Overheating Mitigation to become Regulated

The proposed Approved Document ‘[X]’ prioritises key design changes to mitigate overheating, taking the London Plan cooling hierarchy approach nationwide. It will compel design teams to consider overheating mitigation in conjunction with noise, air quality, safety and security.

The consultation version of the guidance provides two approaches for developers to choose from:

• Option 1: Simplified method – prescribes a maximum amount of glazing (as a percentage of floor area), minimum free openable area for natural ventilation, and requires external shading on east, south and west facing façades;
• Option 2: Dynamic thermal analysis – allows a more flexible approach to demonstrate thermal comfort in accordance with CIBSE TM59, with some modifications to the way the modelling is carried out to allow for more realistic occupant behaviour.

Our initial investigations suggest that Option 1 is most likely to change the look of the façade by reducing window sizes and limiting full-height glazing. Whilst Option 2 provides more flexibility around the strategy, it will push developments towards the general principles of Option 1 (reduced glazing, maximised window openability and external shading).

Whichever option is selected, it is highly likely that compliant strategies will be more onerous than currently.