Overheating in our homes is likely to become increasingly common with global warming. It’s currently 32deg according to BBC Weather. It’s too hot. So how do we keep our homes cool?
It may be particularly uncomfortable today, but in the UK, cold weather is far more of a danger to life than heat. Overheating accounts for about 2000 deaths a year. Cold weather accounts for 25,000 a year (Overheating in New Homes, NHBC, 2012). There are a number of sources of heat; external air temperature, solar gain through the building fabric (walls / roof / floor), solar gains through the windows, internal heat gains (people, computers, ovens, every electrical item…)
Design of homes has a lot to play in overheating. We can’t get away from the fact we need homes, and we can’t build them all on huge plots with big gardens. Like it or not, we have cars, and need somewhere to park them. We need roads to drive on. These hard surfaces re-emit the heat back into the surroundings more than natural landscapes. These environments can also discourage the occupants from controlling their environment. If you live on a busy road, opening a window onto traffic isn’t as enticing as opening your window onto a large garden.
Ventilation is important. Ideally, we want through ventilation (or stack ventilation, but that doesn’t help with existing houses). Opening windows on BOTH sides of the house helps to pull the cool air from one side to the other. Even on days like today, there is cooler air on one side of your house. The prevailing wind will naturally pull air through from one side of the house to the other.
Air movement helps our bodies cool. Fans to increase the air movement further will have an impact on how your feel, but they are not a replacement for good ventilation.
The most important thing is to purge your home at night. I know for a lot of people this might be less comfortable, but you need to keep the lower windows open (ground floor) as well as bedroom windows to let the heat of the day escape. Some houses have secure louvres at lower level so they can be left open whether you are in or not. If you don’t let the heat out, the temperatures will only grow.
Closing your curtains will not keep the heat out. The sun will heat the air between the glass of the windows and your curtains – i.e. the heat is still in your house. It can also stop an air flow through, so really you want them open. Internal shutters can sometimes work as the air can still pass through, but to limit the gains through the glazing, you’ll need external shading. Think France / Italy / Spain where they use shutters on the outside of their houses. In Islamic countries, they have beautiful screens called mashrabiya.
In the UK, we are reliant on the sun for heat – the majority of our year is cold rather than hot, so in the winter we want the sunlight to enter our houses and warm the space. That’s where the principle of shutters are ideal. They’re controllable by the occupants.
Planting is also brilliant, especially if you have a deciduous plant where the leaves shade in summer but the branches let the sun in during the winter. Plants also ‘sweat’ water vapour, which further cools the air.
High levels of insulation is not a cause of overheating in houses. It keeps the heat in, but also keeps the heat out. What is more of an issue is the lack of thermal mass in new buildings. That is if you think about a Victorian terrace house, it’s solid brick. That mass absorbs the heat during the day when temperatures are higher and releases it back during the night when temperatures are cooler. Newer building tend to be built of lighter materials, such as timber frame. This is a more sustainable way of construction than concrete, but it’s a balancing act between light weight construction and the benefit of thermal mass.
If you’re thinking about a really big project, looking back at designs of the past can give some ideas you might want to consider incorporating.
High ceilings – The high ceilings of the past got lower, partly to help with winter heating, but high ceilings do help to keep rooms cooler.
Designing houses around courtyards create a shaded space, especially if there’s a pool or fountain incorporated.
A porch / veranda – the shading of a porch can help with heat gains through windows but also create an outside room that can be used in nice weather. Think of it as a room, where children can play when it’s wet, you can work outside when it’s hot.
The Romans ran water through the walls of their houses to cool them. They had underfloor heating too. This quote is by Vitruvius from the late 1st Century BC. Much is still relevant today, even if we have forgotten it.
“We shall next explain how the special purposes of different rooms require different exposures, suited to convenience and to the quarters of the sky. Winter dining rooms and bathrooms should have a southwestern exposure, for the reason that they need the evening light, and also because the setting sun, facing them in all its splendour but with abated heat, lends a gentler warmth to that quarter in the evening. Bedrooms and libraries ought to have an eastern exposure, because their purposes require the morning light, and also because books in such libraries will not decay…
Dining rooms for Spring and Autumn to the east; for when the windows face that quarter, the sun, as he goes on his career from over against them to the west, leaves such rooms at the proper temperature at the time when it is customary to use them. Summer dining rooms to the north, because that quarter is not, like the others, burning with heat during the solstice, for the reason that it is unexposed to the sun’s course, and hence it always keeps cool, and makes the use of the rooms both healthy and agreeable. Similarly with picture galleries, embroiderers’ work rooms, and painters’ studios, in order that the fixed light may permit the colours used in their work to last with qualities unchanged.”