BRITISH ROCK
How energy efficient are the walls in century-old homes in the English countryside?
Ever wondered about the energy performance of a granite and gypsum-skinned farmhouse in Oxenham, or a cottage in Selborne with walls made of straw, clay, cedar and an air space?
No one had ever checked, until the Society for the Protection of Ancient Buildings began taking U-value measurements last year.
The group found the farmhouse, for example, had a U-value of 1.27 (roughly R-1) and the cottage stood at 0.28 (R-3.5). But walls that average 16 in. thick make a difference. In 79% of the 30 buildings studied, including the farmhouse and cottage, heat loss was less than a widely used thermal performance software had calculated.
The society performed this research out of concern that homeowners were mucking up historic buildings with wall insulation in the name of energy efficiency. Old walls made of traditional materials were meant to breathe and shed dampness, the group said, and shouldn’t be judged solely by U-values.
The fieldwork, done by Caroline Rye at the University of Portsmouth, is continuing with research into air tightness, moisture and air quality.
“Research within the UK is still at quite an early stage,” Rye said. “There is probably a role for improving thermal performance by improving airtightness, but the degree of permeability needs to be carefully considered to avoid long-term damage to the fabric of traditional structures, as well as avoiding adverse consequences for human health.”
Worried that homeowners in the United Kingdom are ruining historic walls in the name of energy efficiency, the Society for the Protection of Ancient Buildings sponsored a first-of-its-kind study of heat loss. A sensor attached to this 25-in.-thick wall made of granite and slate recorded a U-value of 1.25, or roughly R-0.8. But the society maintains that U-values are an inadequate way to judge the performance of old walls, which benefit from their thickness and ability to breathe and shed dampness.
10.2011
29
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