Residential developments in London must be fitted with windows up to 60% smaller than anywhere else in the UK, according to new measures outlined in the consultation document for new building regulations.
The measures will apply to all new homes and residential institutions, including student halls of residence, from 2021; the aim of which will be to improve compliance with proposed new regulations on overheating in new homes.
Government research shows that most new homes will overheat during warm summers, with the problem particularly acute in London due to higher average temperatures.
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 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 consultation is due to open on 13 April.
Read next: Sustainability Showcase | CHP
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