Why New Zealand houses are cold (even the new ones)

The wall is mostly insulation. Or is it?

A timber wall is studs, plates and nogs with insulation fitted in between. Timber lets heat through far more easily than insulation does, so every piece of framing is a small gap in the blanket. BRANZ, New Zealand's building research body, measured 47 new houses and found that, on average, more than a third of the outside wall area was timber framing. Regulators and the industry had assumed far less.

What that does to the numbers

In a later study, BRANZ found that a standard 90 mm timber wall with R2.8 insulation installed (an R-value measures how well something resists heat; higher is better) performs at about R1.2 to R1.4 as a whole wall. The calculation used for Building Code compliance gives that wall R1.9 to R2.0. The insulation on the label isn't what the wall delivers.

Why it's hard to fix with timber

BRANZ also found little framing that could simply be removed. Even an experienced detailer, working on a simple design, couldn't get framing below 25% of the wall. Some builders already add a second layer of insulation, which BRANZ says creates a thermal break between the framing and the outside.

The other half: how the insulation is fitted

Batts are fitted by hand, between framing, on site. Over the years they can slump, squash down or get damp, and every gap lets heat out.

What you can do in the house you have

Look up into the ceiling and under the floor, where insulation is easiest to check and top up. Use thermal curtains, and stop draughts at doors and windows.

How we approached it

Our wall panels have no studs inside them. The insulation fills the whole panel and is bonded to the steel faces in the factory, so it can't slump.

Reviewed October 2026.