Find out whether a building will overheat, before it is built.

Why it matters now

Summers in the UK are getting hotter, and London is warmer than its surroundings because of the urban heat island effect. Homes built to be airtight and well insulated keep heat in during winter, but they can also trap it in July. Bedrooms that stay too warm at night are the most common complaint.

Part O of the Building Regulations

Since June 2022, new homes in England must meet Approved Document O. It limits how much solar heat gets in and requires a way to remove excess heat. There are two ways to show compliance:

• The simplified method sets fixed limits on glazing and openable area. It is stricter in parts of London, and can force smaller windows than the design wants.
• Dynamic thermal modelling to CIBSE TM59 tests the actual design hour by hour through a hot year. It often allows more glazing, as long as shading and ventilation are shown to work.

Overheating and planning in London

The London Plan asks developments to reduce overheating through the cooling hierarchy, starting with design measures before relying on air conditioning. Many London boroughs expect an overheating assessment as part of the energy statement for larger residential schemes. We prepare it in the format the council expects.

For your own extension or loft

Extensions are not covered by Part O, but they are where overheating most often goes wrong. A south or west facing glass box can become a room the family avoids for two months of the year. Modelling it at design stage shows which changes make the real difference, such as glass specification, an overhang, external blinds or roof lights that open.

Who carries it out

Assessments are carried out by Dana, who holds an MSc in Design and Management of Sustainable Built Environments from the University of Reading, with a focus on dynamic thermal modelling in IES-VE. More about the team.