uPVC windows in New Zealand: how they compare

uPVC is one of the best-insulating window frames sold in New Zealand. BRANZ lists it at the top of the common frame materials for thermal performance, and in the H1/AS1 5th edition table a uPVC window with basic double glazing rates R0.40, against R0.26 for the same glass in a plain aluminium frame and R0.32 in thermally broken aluminium. The catch is that uPVC means replacing the whole window, and NZ products vary.

What is a uPVC window?

uPVC is unplasticised polyvinyl chloride, a rigid plastic extruded into hollow, multi-chambered frame sections. In a window the chambers trap air, which is why the frame conducts much less heat than aluminium. BRANZ notes that uPVC frames typically include a steel stiffener for strength, and that the things to look at are UV resistance, the frame construction, the hardware and the finish, which can be natural uPVC, an aluminium facing or a PVC laminate. Opening styles include tilt-and-turn, casement, awning, sliding and double hung.

How does uPVC compare with aluminium and timber?

BRANZ lists window frame materials in approximate increasing order of thermal performance: aluminium, steel, thermally broken aluminium, thermally broken steel, composite timber and aluminium, timber, fibreglass, uPVC. Its H1 bulletin puts it more simply: timber and uPVC frames offer the best thermal performance because they are relatively poor conductors of heat, followed by thermally broken aluminium. Plain aluminium is the poorest, because aluminium conducts heat so well.

Two things stand out. First, the frame makes a big difference with the same glass: a basic double-glazed unit in uPVC (R0.40) beats a low-E, argon-filled unit in plain aluminium (R0.30–0.37). Second, uPVC and timber sit close together, with timber slightly ahead in this table. That differs from BRANZ's ranking, because the table also reflects how much of each window is frame (23% for aluminium up to 41% for timber, BRANZ says), not just the material.

BRANZ adds a caveat on the uPVC column: there is considerable variation in uPVC products in New Zealand, so the uPVC results may be less representative than the aluminium ones. Some uPVC suppliers may struggle to meet these figures; others will easily exceed them. Treat the table as a guide, and ask for the actual window's R-value, ideally from a WEERS rating (the Window Energy Efficiency Rating System BRANZ developed with the Window and Glass Association).

Does uPVC meet the H1 building code?

For new windows under the 5th edition of H1/AS1, the Schedule Method minimum is R0.46 in climate zones 1–4 and R0.50 in zones 5–6 (BRANZ). Read across the table: basic double glazing in uPVC (R0.40) falls short, but uPVC with low-E and argon (R0.50 and up) clears both thresholds. A plain aluminium window doesn't reach R0.46 with any double glazing in the table. The 6th edition, published 27 November 2025, removed the Schedule Method, and the 5th edition can be used until 26 November 2026. See H1 and your windows.

BRANZ also points out one practical advantage. A thermally broken aluminium frame only performs if it is installed so the inner half of the frame isn't exposed to outside air. uPVC and timber don't depend on that, so a less-than-ideal installation costs them less.

Can you retrofit uPVC into existing frames?

No. uPVC is a frame material, so getting uPVC means taking the old window out and putting a new one in. If your joinery is sound and you want to keep it, retrofit double glazing puts a sealed unit into your existing timber or aluminium frames instead. The two routes are compared in retrofit vs replacement windows.

How much do uPVC windows cost in NZ?

We haven't found an independent New Zealand price for uPVC specifically, so we won't invent one. What is published is the price of replacement windows in general: CheckMyBuilder puts full replacement at $800–1,600 per m², and Wellington Glass at $1,500–2,500+ per opening. The one frame uplift we have a source for is thermally broken aluminium, at 25–40% on the joinery (Superior Renovations). Get uPVC and thermally broken aluminium quoted side by side for the same openings and the same glass, and compare the R-value each quote states. What replacement involves.

uPVC or thermally broken aluminium?

• For warmth per dollar of glass, uPVC does more with the same unit: in the table it beats thermally broken aluminium by about R0.08–0.22 across the double-glazing options.
• For slim sightlines and big sliders, aluminium is the usual choice: it is stiffer, so frames can be thinner and doors larger.
• For colour and look, aluminium comes in a wide powder-coat range; uPVC is often white, with laminated or aluminium-faced options. Ask what the finish is and how the supplier backs it against UV.
• For the installer, ask how the window sits relative to the wall insulation. BRANZ says installing in line with the insulation layer gets more from any thermally efficient frame.

What to ask for on a uPVC quote

1. The whole-window R-value for each window, and how it was worked out (WEERS or the H1/AS1 method).
2. The glazing unit: low-E or clear, gas fill, cavity width, and spacer type.
3. Whether the frame has a steel stiffener, and the UV and colour warranty on the profile.
4. The warranty on the sealed unit, separate from the frame warranty.
5. Whether the job needs consent. Like-for-like replacement in an existing house of up to two storeys is usually exempt; the conditions.