Double glazed window replacement
New joinery and new glass, for when the frames have had it, the opening is changing, or you want a thermally broken frame that a retrofit can never give you.
Full window replacement takes the whole window out — frame, sashes and all — and fits a new, factory-glazed double glazed window. It costs $800–1,600 per m² of glass (CheckMyBuilder and retroGLAZE, checked 15 Sep 2026), with a per-opening floor of $1,500–2,500+ (Wellington Glass), so roughly double a retrofit.
When replacement is the right answer
- The joinery has failed: rot, corrosion, distortion, or a window that no longer closes and seals.
- You want a thermally broken frame. Retrofit leaves the frame you have; only a new window can fix the frame as a heat path.
- The opening is changing — bigger, smaller, a door where a window was.
- You are mid-renovation with the linings off, when the marginal cost of doing it properly is lowest.
What you are paying for
| Item | Range | Source |
|---|---|---|
| Per m² of glass | $800–1,600 | CheckMyBuilder, retroGLAZE |
| Per opening (floor) | $1,500–2,500+ | Wellington Glass |
| Thermally broken aluminium joinery | +25–40% | Superior Renovations |
| Low-E / high-performance glass | +5–10% | Wellington Glass |
| Scaffolding, two storeys or more | $1,000–5,000 | CheckMyBuilder |
Frame choices
New Zealand replacement joinery is mostly aluminium, thermally broken aluminium, uPVC or timber. The choice changes the price and the frame's contribution to heat loss; it does not change the glass. We publish the joinery uplift we have a source for — thermally broken aluminium at 25–40% (Superior Renovations, Sept 2026) — and leave the rest to your written quote, which should state the exact system and its warranty.
Consent, contracts and the $30,000 line
Like-for-like replacement in the existing opening is usually exempt from building consent under Schedule 1 Exemption 8, in a dwelling of up to two storeys, where the existing window has not failed its 15-year durability requirement. Separately, residential building work of $30,000 or more including GST needs a written contract, with a disclosure statement and the MBIE checklist given before signing. We give both on every job.
What our estimate does not include
Repairing framing or linings found once the old window is out, reinstating interior and exterior finishes beyond making good, refitting curtains and blinds, and repainting. Those are quoted after the measure, or listed as variations, rather than buried in a per-m² rate.
Window replacement questions
How much does double glazed window replacement cost in NZ?
$800–1,600 per m² of glass (CheckMyBuilder and retroGLAZE, checked 15 Sep 2026), with a floor of $1,500–2,500+ per opening (Wellington Glass). Thermally broken aluminium adds 25–40% to the joinery (Superior Renovations, Sept 2026).
Why is replacement roughly double the price of retrofit?
You are buying a whole new window, not new glass. New joinery, factory glazing, removal of the old unit, flashing and making good the reveal and the exterior all sit in the price.
What is thermally broken aluminium?
Aluminium joinery with an insulating barrier through the frame, so the frame itself is much less of a heat path. It is the one thing a retrofit cannot give you, and it adds 25–40% to the joinery cost (Superior Renovations, Sept 2026).
Should I choose uPVC or aluminium?
Both are sold in New Zealand and both carry double glazing. We won't rank them here, because we haven't got a New Zealand source that compares them on the terms that matter for your house. Ask for the spec and the warranty in writing on your quote, and compare those.
Does replacement need building consent?
Like-for-like replacement in an existing opening is usually exempt under Schedule 1 Exemption 8, in a dwelling of up to two storeys, where the window hasn't failed its 15-year durability requirement. Enlarging or moving an opening is not exempt. The conditions.
What about the $30,000 rule?
Residential building work of $30,000 or more including GST needs a written contract, and the contractor must give you a disclosure statement and the MBIE checklist before you sign (building.govt.nz). Whole-house replacement often passes that threshold. We use a written contract and give both on every job, whatever the value.
Can I replace some windows and retrofit the rest?
Yes, and it is often the sensible answer: replace what has failed, retrofit what is sound. Price both in the calculator on the same window list so you are comparing the same house.