Research by engineering consultancy Arup for the Climate Change Committee recently revealed the extent to which many London property types breach bedroom overheating guidelines.
The study found that old flats in the capital typically exceed 26C for 182 nighttime hours in a standard year, well above the 32 hours accepted under design assessment rules issued by the Chartered Institution of Building Services Engineers.
If global warming increases the world's temperatures by 2 degrees from pre-industrial levels — the red-alert level scientists are desperate to avoid — this rises to 421 hours of uncomfortable sleeping conditions. Even insulated detached houses would overheat almost seven times more frequently than the guidance allows under these conditions.
So what can you do to keep temperatures down in your bedroom during this heatwave and the ones to follow?
Antonietta Canta, principle environmental and sustainability engineer at Arup and co-author of the Climate Change Committee report, says using your home in the right way can slash your overheating risk by a tenth.
Keep windows and curtains closed against direct sun
While we may be stripping off layers in a heatwave, our homes need added protection.
This starts with the oft-quoted advice to keep windows and curtains closed when the sun is directly on doors and windows, while allowing cooler air in as soon as possible.
More permanent installations such as internal blinds; external shutters or overhangs; and even insulation and reflective paint will be even more effective.
Shutters were found to reduce overheating by more than 20 per cent in a typical ‘old’ London flat - but this obviously comes at a price. Solar reflective paint on outside walls was slightly more effective at a lower cost, Arup found.
“External shading devices are ideal,” says Canta. “Internally, the outcomes of different types of blinds are similar but I think Venetian are the most effective as you can choose the orientation and opening angle depending on the position of the sun.”
Reduce use of heat-emitting equipment
There is far more you can do, however, to maximise your cool, including changing your lightbulbs and thinking twice before you take the iPad to bed with you.
“Reducing the use of heat-emitting equipment, from dishwashers to lights, is really important,” says Canta. “Replace low-efficiency lighting with LED bulbs can help. And having a laptop on is really bad; you can feel the heat coming off it.”
Go window shopping
The age-old debate over whether windows should be closed or open on a hot day misses the point somewhat. Perhaps we should be asking ourselves whether our glass spaces should stay or go.
Arup's research highlighted the huge impact that can be made on temperatures by having the right kind of windows, with overheating reduced by up to a third in some cases.
The key is to ensure you can get as much air in, and keep as much sun out, which relies on openable area and a property known as G-value.
“We notice that in many flats especially there are very big windows but perhaps only a quarter of them can be opened, and maybe only to 45-degrees,” says Canta. “A G-value tells you how much heat is coming in through a window.”
Get active (cooling)
Whether on a bedside table, a stand at the foot of the bed or fixed Central America-style to the ceiling, fans can work wonders for the liveability, or sleepability, of a bedroom.
Although moving air around doesn't technically reduce the level of heat in a room significantly, it can drastically alter the way human beings experience it.
The ultimate measure to cool your bedroom is, of course, installing an air conditioning unit. This can be set to 25C and pretty much elliminate overheating under the CIBSE measure.
But Canta warns this only works to a point. “Air conditioning contributes to the heat in the urban environment so if they were installed everywhere we would make the problem worse and worse.”
Go on holiday
Instead of expensive and ultimately counter-productive electrical cooling, Canta calls for intelligent housing design and operation to make the most of passive measures.
The Arup report goes into a high level of detail about the different types of intervention that can be made, and their relative cost and effectiveness.
But its author thinks a shortcut to all this science and knowledge is to look at how it's been done for years in countries more used to the temperatures we're currently experiencing in the UK.
"I was asked at a conference recently what would be my number one tip for a friend — and I said travel," she says. “People are used to a different type of architecture here but we need to adjust to a changing climate.”