Retrofit double glazing for aluminium windows
The usual answer for a 1970s to 1990s house with cold rooms and wet bedroom windows: new sealed units into the aluminium joinery you already have.
Retrofitting aluminium joinery means fitting a sealed double-glazed unit into the frames you already have. Wellington Glass publishes $550–850 per aluminium window (checked 15 Sep 2026), the cheapest published per-window band in New Zealand, and it is the most common retrofit done here.
Why this is the most common retrofit in NZ
New Zealand built a lot of houses with single-glazed aluminium joinery between the 1970s and the 1990s, and that joinery is generally sound decades later. The glass was the weak part, not the frame, and the glass is the part a retrofit changes. It is also the fastest and cheapest per window, which is why whole-house jobs are realistic.
What it fixes, and what it doesn't
- Fixes: a cold inside pane, and with it most of the morning condensation on the glass. EECA lists a warmer home, lower heating bills and reduced condensation and mould among the benefits of insulating windows.
- Fixes: heat going out through the glazed area. EECA says up to 40% of a home's heating energy is lost through windows, dropping to 25% or less once they are double glazed.
- Doesn't fix: the frame. Plain aluminium conducts, and it is still there after a retrofit. That is what thermally broken joinery is for, and it only comes with replacement.
- Doesn't fix: moisture. If the room is producing more water than it can vent, condensation will find the next-coldest surface.
What the measure checks
- Whether the frame section will take a thicker sealed unit at all — not every aluminium profile will.
- Corrosion, distortion and whether the drainage still works.
- Rollers, tracks, stays and catches, which carry more weight afterwards.
- Sliding doors, which are their own question: bigger units, heavier panels, and often different hardware.
- The exact glass sizes, which is what makes the quote fixed rather than a range.
Retrofit or replace this joinery?
If the aluminium still works and you want warmer rooms for the least money, retrofit. If the joinery leaks, sticks or has corroded, or if the cold frame is the thing that bothers you, price a replacement instead: $800–1,600 per m², or $1,500–2,500+ per opening (CheckMyBuilder, Wellington Glass), plus 25–40% for thermally broken joinery. Our calculator will price your windows both ways.
Aluminium retrofit questions
How much does it cost to double glaze aluminium windows?
$550–850 per window (Wellington Glass, checked 15 Sep 2026) — the cheapest published per-window retrofit band in New Zealand. On area, retrofit runs $450–800 per m² of glass (CheckMyBuilder).
Can old aluminium joinery be retrofitted?
Usually, if it still slides or swings properly and the seals and frame are intact. Aluminium from the 1970s onwards is retrofitted routinely. Corroded, distorted or leaking joinery is a replacement job.
Will it stop the condensation in my bedrooms?
It will reduce it substantially, because the inside pane is much warmer. It won't remove the moisture: that is ventilation's job. What glazing changes and what it doesn't.
My frames still feel cold. Does retrofit fix that?
No, and that is the honest limit of it. Plain aluminium conducts, and a retrofit leaves the frame as it is. If the frame itself is what you want to fix, that is a thermally broken replacement, at +25–40% on the joinery (Superior Renovations, Sept 2026).
Do the windows still slide afterwards?
They should. A sealed unit is heavier, so rollers, tracks and stays are checked at the measure and anything that needs replacing is priced then rather than found on install day.
Is low-E glass worth it on aluminium?
It adds 5–10% to the price (Wellington Glass) and EECA puts the performance improvement from a low-E coating at up to 30%. The calculator shows it as a separate line so you can see the trade for your own windows.
Do I need consent?
Usually not, under Schedule 1 Exemption 8, in an existing dwelling of up to two storeys where the window hasn't failed its 15-year durability requirement. The conditions.