H1 climate zones and window R-values: what the Building Code asks for

What we found

Our calculations, data as of 23 October 2026

1. H1 splits New Zealand into six climate zones by district. Of our 15 cities, Whangārei, Auckland and Tauranga are zone 1; Rotorua and Taupō are zone 4; Christchurch and Dunedin zone 5; Invercargill and Queenstown zone 6.
2. Under the fifth edition’s schedule method, still usable for consent applications made until 26 November 2026, new windows must reach R0.46 in zones 1–4 and R0.50 in zones 5–6. The sixth edition, in force since 27 November 2025, drops the schedule method and checks the whole house by calculation.
3. Of the upgrades for existing single-glazed homes, only low-E retrofits into timber sashes, installed low-E secondary glazing, and new uPVC or timber windows reach those minimums. Any retrofit into plain aluminium frames falls well short (R0.30).
4. The Code’s window table rates the window with its frame. The same low-E glass gives R0.30 in plain aluminium and R0.56 in timber, which is why glass-only R-values in brochures can mislead.

The six zones

The sixth edition of the acceptable solution H1/AS1, issued by MBIE on 27 November 2025, lists the zone for every territorial authority. Zone 1 is the warm north; zone 6 is the inland South Island and Southland. For our cities:

*Fifth edition, schedule method. The sixth edition sets no fixed window minimum; windows are part of a whole-house heat-loss calculation.

The zones are not a simple north–south gradient. Rotorua and Taupō, on the volcanic plateau, are in zone 4, colder on paper than Wellington City, Nelson and Palmerston North in zone 3. Tauranga is zone 1 with Auckland, while Hamilton is zone 2. Our own degree-hour data agrees: Rotorua and Taupō need more heating than Wellington; see heat loss by city.

The window table

H1/AS1 gives whole-window R-values for typical house windows by glass performance (Ug, the glass’s heat transfer; lower is better) and frame:

For housing, these values can be used instead of a calculation. They include the frame, which is why plain aluminium tops out at R0.39 even with the best double-pane glass in the table.

Fifth edition, sixth edition, and what applies when

The fifth edition of H1/AS1 (as amended) can be used for building consent applications submitted before 27 November 2026. Its schedule method sets fixed minimum R-values for each element, including R0.46 for windows in zones 1–4 and R0.50 in zones 5–6. The sixth edition removes the schedule method; designers instead show that the whole house loses no more heat than a reference building.

Which upgrades reach the new-build minimum

Windows in existing homes do not have to meet H1 when you upgrade them. But the minimum is a fair benchmark of a modern window. Against it:

This is the strongest argument for keeping timber frames, and for thermally broken or uPVC frames if you replace aluminium joinery. See glass and frames.

This week: Palmerston North

Single glazing in an aluminium frame runs below the dew point about 2,430 hours a year in Palmerston North (H1 zone 3); clear double glazing cuts that to 350. A low-E retrofit of 25 m² saves $190 a year heated mornings and evenings with a heat pump, or $569 heated all day. Fastest payback here: DIY magnetic secondary glazing, 17 years.

Cheap fix. EECA estimates that closing curtains before dark saves $80–90 a year. Lined, full-length curtains with a pelmet work best. Read more

Read next: Glass and framesReplacement costHeat loss by cityBuilding consentVillas and timber windows