14/05/2026
H1 changes in New Zealand: why "H1 compliant" does not always mean "the warmest window"
New Zealand’s H1 Energy Efficiency requirements have changed, and this is especially important for windows and doors.
From 27 November 2025, the new H1/AS1 Sixth Edition applies. One of the key changes is that the old schedule method has been removed. Under the previous approach, people talked a lot about windows needing to achieve simple minimum values such as R0.46 or R0.50, depending on the climate zone.
The new approach is different.
Instead of asking whether each individual window reaches one universal number, H1 now looks at the performance of the whole building thermal envelope through the calculation method. In simple terms, the house is assessed as a complete system: roof, walls, floor, windows, doors and glazing area all together.
This change does make sense. A single R-value for every window was simple, but not always perfect. Real window performance depends on the window size, the frame-to-glass ratio, the opening type, the glass unit, Low-E coating, argon gas, spacer type, the total glazing area in the home, and the insulation levels in the roof, walls and floor.
For example, a small window and a large window do not behave the same way thermally. A small window can have a higher proportion of frame compared with glass, while a large window depends more heavily on the glass unit. So assessing the whole building envelope can be more realistic than using one fixed number for every window.
But there is also an important concern.
Under the calculation method, it may be possible for a house to pass H1 even if one small window has weaker thermal performance than the old R0.46 requirement. If the home is well insulated and the window area is small, the overall calculation may still pass.
That means "H1 compliant" does not automatically mean that every window is the warmest or best-performing option.
This is especially important with standard aluminium joinery. A good glass unit, for example Low-E, argon and a better spacer, can help aluminium windows meet the overall H1 calculation. From a compliance point of view, that may be acceptable.
But the physical issue of a cold aluminium frame does not simply disappear... Read more (https://upvcnz.co.nz/blog/new-h1-rules-why-window-frames-still-matter)
