One of the big news stories of the year has been rising energy prices. The cost of domestic gas, oil and electricity has rocketed, and is already double or treble what it was this time last year. So there is a big clamour for British homes to be better insulated, so that we need less energy to heat them in winter.
Some campaigners have been gluing themselves to motorways in an attempt to force Her Majesty’s Government to insulate homes for free. Professional Builder readers will no doubt have their own views on the legitimacy of these tactics!
Also, improving the energy efficiency of older buildings is not quite as simple as the campaigners would have us believe. Whacking in a few slabs of insulation board can create problems that weren’t there before – chiefly by trapping moisture behind them.
Furthermore, there is some question over whether insulating older, solid-walled homes has quite the benefit that campaigners claim. The gold standard of heat-loss calculations has always been the “U value” – measured in Watts per Square Meter per Degree C. Every building material has its U value, which is recorded in tables and websites, and in the manufacturers’ sales brochures.
So if you are building a cavity wall, say, then you combine the published U values of the brickwork, the cavity insulation, the blockwork, the drylining, the plaster skim, and you come up with a magic number that you hope will satisfy the latest version of the Building Regulations. It goes without saying that older houses, built with solid brickwork, and without the benefit of modern insulation materials, are assumed to have much higher U values, and will therefore lose more precious heat (U values are like golf scores – the lower the better.)
But the problem with U values is that they are largely theoretical. When the actual heat loss through a real wall, in a real lived-in house, is physically measured, it can turn out to be rather different from the scientists’ calculations. The Society for the Protection of Ancient Buildings has found that the heat losses through some solid masonry walls might be only half as much as estimated by the U value calculations.
And the most significant factor is making sure the wall stays dry. (Air trapped in materials is good, while moisture trapped in materials is bad). Hence the problem with sticking modern insulation onto solid walls. Whether it’s internal or external, it can trap moisture and encourage the loss of heat.
Remember, draught-proofing doors and windows is still the single most cost-effective thing you can do to stop heat loss, and upgrading loft insulation is also essential.
But thoughtlessly insulating older solid walls might actually cause more harm than good, whatever the loony protesters say. This story still has some way to run.
