London homes to have smaller windows than rest of UK

Residential developments in London will have to be fitted with windows up to 60% smaller than elsewhere in the UK to comply with proposed regulations to control overheating in new homes.

The measures are included in a consultation document for new building regulations launched last week and will apply to all new homes and residential institutions including student halls of residence from 2021.

Government research has revealed that most new homes will overheat during warm summers with the problem particularly acute in London due to higher temperatures than elsewhere in the country. Climate change is set to make the problem worse.

The draft regulations propose that new London homes fitted with windows on opposite facades cannot have a window area greater than 13% of the floor area. Similar homes built elsewhere in England will be permitted to have a window area up to 21% of the floor area.

External shutters, overhangs or high-performance solar control glass will also be compulsory in London on the south, east and west elevations of a development to control solar gain.

Internal blinds and nearby trees will not be allowed to count as solar shading.

Homes will also need to include an unrestricted ventilation area equivalent or greater than the glazing area to remove excess summer heat. Windows must be designed to open to a minimum of 60 degrees with new minimum window threshold heights on upper floors to mitigate the risk of people falling out of open windows.

Developers will be able to use dynamic thermal modelling as an alternative to prescriptive window sizes and solar shading which may provide some flexibility in situations where a development is heavily shaded by adjacent properties or landscape features.

Government figures show the measures should save developers money as solid walls cost less than glazing. The impact assessment, which accompanies the draft regulations, states the savings add up to £5,147 for the average home.

The proposals are part of a consultation on proposed changes to Parts L and F which control energy and ventilation respectively; the new overheating regulation hasn’t yet been assigned a letter.

The consultation is open until 13 April.