Costs · retrofit
Retrofit double glazing cost in New Zealand (2026)
A retrofit keeps your frames and swaps the single glass for sealed double-glazed units. It is the most common upgrade for older New Zealand homes, and quotes vary more with the frames and access than with the glass.
What would your windows save?
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What we found
Our calculations, data as of 23 October 2026
- For 25 m² of windows, about a three-bedroom house, a low-E retrofit costs around $15,000 in aluminium frames. Glaziers’ 2026 quotes put typical whole-house retrofits between $10,000 and $25,000.
- Low-E glass adds roughly $80–150 per m², and argon $50–100 per m². In a plain aluminium frame the low-E unit lifts the window only from R0.26 to R0.30, because the frame leaks heat. In timber frames it goes from R0.44 to R0.56, so low-E is worth more there.
- Retrofit costs about half as much as new joinery for the same area: $15,000 against $31,300 for new uPVC windows, for a saving that is only $90 against $126 a year in Auckland.
- Timber sashes cost more to retrofit (about $750 per m² against $600 in aluminium), because each sash is routed out by hand to take the thicker unit.
| New timber, low-E | $42,500 |
| New uPVC, low-E | $31,300 |
| New thermally broken aluminium, low-E | $28,800 |
| Retrofit double glazing, low-E argon | $15,000 |
| Retrofit double glazing, clear | $12,500 |
| Installed low-E secondary glazing | $11,300 |
| DIY magnetic secondary glazing | $3,800 |
Mid-points of 2026 installed price ranges, including GST, for single-glazed aluminium windows. Excludes scaffolding and repairs.
What a retrofit is
In an aluminium window, the glazier removes the single pane and fits an IGU, usually with a new glazing bead or an adapted sash, since the old rebate was cut for a single sheet. In timber, the sash rebate is routed deeper to take the unit, which is skilled hand work and why timber retrofits cost more. Frames, sills and linings stay, so there is usually no plastering or repainting and the job is often done in a day or two.
Prices by window area
Our model uses the mid-points of the installed per-m² ranges New Zealand glaziers and cost guides published in 2026, GST included. For windows in aluminium frames:
| Option | 10 m² | 15 m² | 25 m² | 35 m² |
|---|---|---|---|---|
| DIY magnetic secondary glazing | $1,500 | $2,300 | $3,800 | $5,300 |
| Installed low-E secondary glazing | $4,500 | $6,800 | $11,300 | $15,800 |
| Retrofit double glazing, clear | $5,000 | $7,500 | $12,500 | $17,500 |
| Retrofit double glazing, low-E argon | $6,000 | $9,000 | $15,000 | $21,000 |
| New thermally broken aluminium, low-E | $11,500 | $17,300 | $28,800 | $40,300 |
| New uPVC, low-E | $12,500 | $18,800 | $31,300 | $43,800 |
| New timber, low-E | $17,000 | $25,500 | $42,500 | $59,500 |
And for timber frames, where only the retrofit and secondary options keep the frame:
| Option, timber frames | 10 m² | 15 m² | 25 m² | 35 m² |
|---|---|---|---|---|
| DIY magnetic secondary glazing | $1,500 | $2,300 | $3,800 | $5,300 |
| Installed low-E secondary glazing | $4,500 | $6,800 | $11,300 | $15,800 |
| Retrofit double glazing, clear | $6,500 | $9,800 | $16,300 | $22,800 |
| Retrofit double glazing, low-E argon | $7,500 | $11,300 | $18,800 | $26,300 |
Per window, 2026 quotes run roughly $400–850 for an aluminium retrofit and $800–1,200 for a timber sash. A standard window is around 1.5 m², so 15 windows is close to our 25 m² case.
What changes a quote
- Low-E and argon. Low-E adds about $80–150/m², argon $50–100/m². Worth it in timber; marginal in plain aluminium.
- Scaffolding. Upper-storey windows on a two-storey house can add $1,000–5,000.
- Frame repairs. Rotten timber or pitted aluminium needs fixing first; a retrofit cannot save a failed frame.
- Ranch sliders and large panes. Big units are heavy and may need toughened or laminated glass where the Code requires safety glass.
- Measure-and-quote fees. Some firms charge around $150, credited against the job.
What it saves
With a heat pump used mornings and evenings, a low-E retrofit of 25 m² saves about $90 a year in Auckland, $128 in Wellington and $186 in Christchurch. In homes heated all day, savings are about three times higher; see is double glazing worth it for every city and heating pattern.
Consent
Replacing glass in an existing window is building work that is generally exempt from building consent under Schedule 1 of the Building Act, unless a window installed within the last 15 years has failed, for example by letting water into the wall. Exempt work still has to comply with the Building Code. See building consent for windows.
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