R VALUE FOR SOLID WOOD
This is a reprint of a recent article on some studies done to
show that the straight R-value of solid wood is misleading. Even
though it seems worse than other materials, because wood has a
lot of mass it actually can store energy, not just prevent the
ingress ( or egress) of energy, which is only what R-values
Wood insulation properties studied
Lincoln University researchers have studied the paradox of
houses built from solid wood seeming to have greater levels of
heat retention and coziness 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
“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 favorably. 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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