The present uncharactersitic British summer heatwave has prompted a plethora of news articles on how to stay cool. An article in the Times, for example, covered dietary considerations ("In order to stay as cool as a cucumber, eat cucumbers"). But how do you keep your house cool? Do you open windows (to encourage a breeze), or close them? Should you draw curtains?
A reader (Michael Greenhill) in the Telegraph this week writes: "When I served in India 60 years ago, the daily temperature was frequently 112F. I was lucky enough to occupy a stone-built bungalow with thick walls. My daily rouine was to close all windows and doors during the day, and keep them closed until the evening, when everything was opened up until the morning, and closed again until the sun rose. Woe betide anyone who left an outside door open."
This makes a lot of sense: when the air temperature outside the house is higher than inside, one will want to keep the outside air out and the inside air in. The trick is to make sure that the inside air actually is cooler. It might not necessarily be so.
The fabric of any building will tend to absorb heat during the day, and radiate it at night, rather like a storage radiator. Thinner buildings will heat up and pass heat through to the interior more quickly. Thick, stone-walled buildings will absorb a lot more heat but will transfer it inwards more slowly. By ventilating the interior with cooler night air, the effects of internal radiation will be minimized. Keeping out the warm daytime air helps too.
Were it quite that simple. Houses are not purely stone boxes: they have windows and roofs, and most are not even constructed of stone. Glass windows allow huge amounts of solar radiation in, which is why most European houses have shutters to keep out the light, or rather heat. Roof construction is critical: dark slate tiles will absorb and transmit large amounts of heat. A tiled construction that allow for ventilation is important: warm air rises, and if it is allowed to escape through the roof it will be replaced by cooler air at ground level. Ironically, a hefty dose of loft insulation will keep warmth in during summer as well as winter. And, of course, one likes to cook...
There is also the problem that leaving all windows and doors open at night is a real security issue for many.
Your mileage therefore will vary, as they say. We are fortunate to live in a large, three-storey stone built house, though one that is south-facing and has plenty of windows (and no shutters), and good loft insulation. The inside temperature varies much less than the outside, and typically the inside is cooler than the outside during the day, with the converse at night. Our strategy is to have as many windows and doors as we safely can open at night whilst keeping shut as many as we can bear to during the day, with curtains drawn in sun-facing windows. That seems to be working well, but temperatures here have only reached 35°C (95°F); 112°F might well be a different matter.
Interestingly, the coolest the interior of our house has felt in any summer's heat is on arrival back from holiday when it has been shut up completely, day and night, for several days.
Comments (1)
Yup, you scientists have got it right. Our house (in the Loire valley) stayed cool through two weeks of +40ｰC using roughly the same methods. To avoid security risks, I rose at six every morning to open the house downstairs. Since the outside temperature had not significantly dropped till about five, there was no need to open up earlier anyway. All was shut on the south side at 8.45am with curtains drawn. North side was left open a little to catch what breeze there was. The 16th century builders had also worked out the angle (it is not EXACTLY south facing), the thickness of the walls and the height of the windows. Therefore the sun doesn't come into the house during the summer (but streams in during the winter). The main heat generator was the 1950s terrace which needed hosing down occasionally. In the afternoon, we opened the north facing veluxes to let out accumulated heat trapped by our brilliant insulation in the attic. (That's the theory anyway!) And so all visitors after a journey would enter the house with a grateful gasp at the coolness they encountered. And may the great weather continue..the grape harvest promises the best since those vintages referred to in old novels....
Posted by Nicholas Bunch | August 26, 2003 11:03 PM
Posted on August 26, 2003 23:03