This article originally appeared in Green Building, Spring 2014
“Everybody loves the summer time”, as Carole King once sang: everybody that is, except those who are separated from their sweethearts – and those sweltering in stifling buildings that they just can’t get cool.
At its worst, overheating can be a serious – even fatal – health issue, with the very elderly, and babies and small children most vulnerable, and heart attack, stroke, and sudden infant death all possible consequences. But much more commonly it is a discomfort issue, which can affect the usability of buildings, and/or drive people to deploy energy-consuming measures such as artificial cooling.
A building that cannot be cooled down to a comfortable temperature whatever you do is obviously overheating. One that cannot be cooled in a secure and comfortable way (eg, can only be cooled via opening window onto a busy road, or by leaving patio doors open at night), overheats so far as the occupants are concerned. Both are a failure on the part of the design and construction team.
How hot is too hot? The occupant has the last word on this, but designers do need guidance on what ‘most occupants’ can cope with:
As the National Housebuilding Council reports, work by CIBSE and Arup suggests that most people begin to feel ‘warm’ at 25ºC and ‘hot’ at 28ºC. At 35ºC “there is a significant danger of heat stress.” Heat at night bad enough to interfere with sleep seems to compound the danger to health.
In practice, comfort also depends quite a lot on humidity (which determines how readily people can keep themselves cool via sweating) and air movement (ditto) .
In general, it ought to be possible to avoid overheating without sacrificing winter time comfort and energy efficiency. Despite a warming climate we’re still going to want houses (in the UK) warmer inside than out, most of the year. Continue reading