The New Zealand Building Code now requires thermally broken joinery in new homes. But what exactly does that mean—and what are the benefits?
Double glazing has long helped regulate indoor temperatures. It works by trapping a layer of air or argon gas between two panes of glass, slowing down heat transfer. A thermal break takes this a step further. It separates conductive materials like aluminium or glass using materials that don’t conduct heat well. This reduces heat loss and gain through the joinery.
A thermally broken window includes a low-conductivity material that separates the inner and outer aluminium frames. It also adds a thermal barrier between the panes of glass. This “break” prevents heat from easily moving between the inside and outside surfaces. Essentially, the aluminium frame is split into two parts that don’t touch.
Windows are a major source of energy loss in most homes. Traditional aluminium frames allow up to eight times more energy to escape than an insulated wall of the same area. In contrast, thermally broken joinery paired with high-performance glass can achieve an R-value of up to R0.8. Standard non-thermally broken aluminium joinery typically reaches only around R0.33.
During winter, regular aluminium frames can become as cold as the outside air. This can create the feeling of a draft, as warm indoor air cools rapidly near the cold frame and begins to circulate.
In summer, these frames also help by limiting the amount of external heat entering the home. The result is a more stable, comfortable indoor climate across all seasons.
Thermally broken joinery helps prevent condensation. Because the inner frame stays warmer, it is less likely to collect moisture from indoor air. This keeps your windows clearer and reduces the risk of mould or dampness around frames.
Learn more about thermally broken joinery at wganz.org.nz
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.
