Thermal Bridging: When Build Magazine Finally Admits What We've Known

In a recent issue, Build Magazine finally admitted what has been obvious to anyone who thinks about building physics: timber studs are a significant thermal bridging problem in conventionally framed buildings.

For decades, the industry standard has been to fill the space between timber studs with insulation and call it done. But timber itself has an R-value of roughly R0.25 per 25mm. At 140mm deep (standard for 90mm framing with service cavity), a stud delivers only about R1.4 — compared to R3.6+ for the insulated cavity beside it.

The studs act as thermal bridges. Heat flows through them at roughly three times the rate it flows through the surrounding insulation. In a standard house, timber framing covers around 25% of the wall area — meaning a quarter of your wall is conducting heat straight out of the building.

Build Magazine's Proposed Solution: Double Framing

Build Magazine's suggested fix is a double timber frame — essentially building two walls offset from each other so the studs don't align, then filling the space with insulation. It's an improvement in thinking. It would reduce thermal bridging significantly.

But there is probably an easier solution.

A SIPs wall has no studs to bridge through. The insulation is continuous from one side of the panel to the other. There are no thermal bridges at all. The R-value of the panel is the whole-wall R-value — no derating factor needed.

So Build Magazine's suggestion is essentially: build more wall to reduce the impact of a flawed system. The SIPs approach is: build one wall and get the performance you paid for.

Why This Matters

This isn't an academic argument. Thermal bridging directly affects how warm your home stays, how much you spend on heating, and whether condensation forms on cold surfaces inside your walls (which leads to mould and rot).

New Zealand has been slow to acknowledge this problem. The H1 changes are forcing higher R-values, but they can't fix bad physics. A double-stud wall with R7.0 insulation between the studs might still have an effective R-value below R5.0 — because the studs are still there, still bridging, still conducting heat.

Sometimes the simplest answer is to remove the bridge entirely.

Previously published on sips.network (2021). Updated for VILA.nz.