Wood insulation properties studied

Thursday 5 Feb 2009

 
Lincoln University researchers have studied the paradox of houses built from solid wood seeming to have greater levels of heat retention and cosiness than the insulation value of the wood wall itself would suggest. On their own, solid wooden walls have a fairly low R-value - meaning that theoretically the walls should not provide a particularly high level of thermal insulation.

"But the R-value is just a measure of the material's resistance to heat flow," Research Engineer Dr Bellamy said. "It only says how much heat is passing through, not how much is being stored." Researchers discovered the answer to this puzzle was wood's superior thermal mass. Having worked extensively with the concrete industry where concrete's ability to store heat is well known, Dr Bellamy was not expecting wood to provide as much thermal benefit as it does.

Traditionally brick and concrete were thought to have superior insulation and passive solar heating properties, but the researchers have shown that somewhat surprisingly, weight-for-weight, solid wood actually has over 2.5 times the thermal mass of concrete.

When comparing walls of the same thickness, due to the different densities of the two materials, concrete will still have greater thermal mass, but the little-appreciated thermal retention properties of solid wood walls means they do in fact play a significant role in regulating the interior comfort of a house.

They store the sun's heat during the day and release it into the house at night. Dr Bellamy used a Danish building simulation model to confirm that when the thermal mass effect was added to the relatively low R value of the external walls, the solid wood house performed very favourably. The thermal performance of the solid wood house was further increased when solid wood internal walls and ceilings were used. "Basically, the more wood you use the better, Dr Bellamy said." Source: NZ Wood


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