A lot has been written about overheating in homes recently, especially in relation to energy efficiency measures introduced under the Green Deal. The BBC quotes Prof Chris Goodier, of Loughborough University’s department of civil and building engineering, who “said the risk of overheating had been overlooked in the ‘big rush to insulate and make homes airtight’, particularly as more extreme weather events, including heatwaves, are being predicted for the UK by meteorologists.” Rory Bergin brings some useful perspective to the debate in his blog and PRP gives an overview in its publication Summer Overheating in Dwellings but I thought it might be helpful for me to pass on some thoughts of my own.
Overheating in summer potentially results in significant energy use for cooling. The first rule is to keep the heat out. While closing curtains or blinds against the sun can help, it tends to trap a layer of hot air between them and the glass which will increase the room temperature. Shading fitted to the outside of the building is the real answer. This is why external shutters, blinds or retractable awnings are a common feature on south- and west-facing windows on the Continent, blocking the heat before it enters the building. To keep heat out it is important that shutters and curtains are closed at sunrise and opened at sunset.
Some buildings are designed with wide eaves to the roofs which help to shade the windows from the high summer sun while still allowing the lower winter sun in to provide warmth. One relatively simple and attractive way of achieving the same result is to build a pergola in front of the ground-floor windows and then to train a vine or other similar climber along the top. This has the great advantage of providing shade in the summer while still allowing plenty of light and useful solar gain to enter the house during winter when the leaves have dropped. Similarly, verandahs can shade the internal area of a house while offering semi-outdoor areas with shelter from the sun and the rain.
A strategically placed deciduous tree is another way of providing natural summer shading, but do ensure it is far enough away from the building to prevent damage to the foundations from the roots.
More high-tech are phase change materials which offer a way of adding thermal mass to structures and stabilising room temperatures. They absorb heat during the hottest part of the day and then release the warmth back into the room as the temperature falls at night.