What the 2022 H1 building code actually requires for windows

The 2022 update to NZ Building Code clause H1 (Energy Efficiency) was the most consequential change to glazing requirements in three decades. It split the country into six climate zones — Auckland is Zone 1, Christchurch is Zone 5, Queenstown is Zone 6 — and set minimum whole-window R-values that can only realistically be met with double glazing using warm-edge spacers and thermally-broken frames. New builds and major alterations now have to meet these minimums or face design refusal at consent.

What counts as a 'major alteration'

The threshold is whether you're applying for building consent. Pure like-for-like replacement of an existing window doesn't trigger H1 — but if you're cutting a new opening, increasing window area, or doing a renovation that requires consent for other reasons, the H1 schedule applies to the windows you're touching. Most ordinary retrofit IGU work doesn't need consent and so isn't bound by H1 — but most installers spec to H1 anyway because it's the new market expectation.

The whole-window R-value targets

These look modest — a single-glazed window typically has a whole-window R around 0.15. A standard argon-filled double-glazed unit in a thermally-broken aluminium frame comes out around R 0.41–0.45, which is at the edge of compliance for Zone 1 and not enough for Zone 5–6. Hitting Zone 5 reliably needs warm-edge spacers, low-E coating, and frame thermal performance to all be optimised — or you go to triple glazing on the cold side of the house.

What this means for the spec sheet

• Argon fill — not air. Marginal cost, meaningful U-value improvement.
• Warm-edge spacer — plastic-foam composite, not aluminium. Eliminates the perimeter cold bridge.
• Soft-coat low-E coating — on surface 3 (the inside surface of the outer pane) for NZ heating-dominant climates. Reflects long-wave radiation back into the room.
• Thermally-broken frame — for aluminium, this is a continuous insulating polyamide strip in the frame profile. Non-negotiable for Zone 5–6 H1 compliance.
• For Zone 6 north-facing-or-larger windows: consider triple glazing.

The retrofit loophole (and why it's not a loophole)

Routine retrofit work doesn't trigger H1 because no building consent is required. So technically you can put any kind of double glazing you like in your existing villa. In practice, the market has converged: nearly every quote you'll get for retrofit in 2026 is to a similar warm-edge / argon / low-E spec because the cost premium over the cheap option is small and the performance gap is large. If you're getting quoted bare-spec double glazing without those line items, ask why.