Heating a timber house: where the money actually goes

Solid wood is a mediocre insulator and an excellent regulator. Understanding which of those you are buying saves more than another twenty millimetres of beam.

The numbers

Pine across the grain conducts at roughly 0.16 W/(m·K). A 200 mm wall therefore sits well below what a current energy standard would ask of a wall alone. In practice houses of this type pass because the losses are distributed: the roof is insulated generously, the windows are good, and the air-tightness at the corners is where the real work happens.

Where the heat leaves

• The roof, if the insulation is thin or compressed at the eaves. Budget 250–300 mm and a ventilated gap that actually ventilates.
• The corners and the crown joint, if the tape was laid in the cold or skipped. A thermal camera on a frosty morning finds this in a minute.
• The windows, where the frame meets the opening. In a timber house that joint moves; it must be sealed with something that moves too.

Insulating from outside — yes or no

If you insulate a glulam wall, do it from outside, with a vapour-open material and a ventilated facade, and accept that the wood disappears from view. Insulating from inside moves the dew point into the beam, which is how you get rot in a house that looks perfect. Most owners who bought glulam for its appearance are better served by spending the same money on the roof and the windows.