The New Zealand Building Code now mandates thermally broken joinery in new homes, but what does it mean and what are the benefits?
Double glazing has long been used to regulate indoor temperatures by capturing a layer of air, or argon gas, between two glass panes, interrupting heat transfer. The process is known as a “Thermal Break,” and it involves separating conductive materials (like glass or aluminium) with poor heat conductors.
A “Thermally Broken Window” refers to a window with a low conductivity material creating a break between the interior and exterior aluminium frame, as well as a thermal break between the panes of glass.
Thermally broken windows offer several benefits.
Windows are a significant source of energy loss, with traditional aluminium frames allowing eight times more energy to escape compared to the same insulated wall area. Higher R values indicate better insulation. Thermally broken frames with high-performance glass can achieve an R-value of up to 0.8. Traditional, non-thermally broken joinery would only offer an R-value of up to R0.33.
In winter, traditional aluminium window frames match the outside temperature, creating drafts when warm indoor air meets the cold frame. In contrast, thermally broken frames are less affected by the exterior temperature, staying warmer and improving temperature stability.
In summer, thermally broken frames also work to minimise heat transfer into the room. Thermally broken frames with high-performance double glazing can achieve an R value of up to 0.8, much higher than standard double glazed frames.
Thermally broken frames also help reduce condensation by maintaining a similar temperature to the room interior, minimising moisture build-up.
Learn more about thermally broken joinery at wganz.org.nz