Retrofit double glazing for timber windows
Sealed units into your existing timber sashes, so the joinery that gives a villa or bungalow its character stays exactly where it is.
Retrofitting a timber window means fitting a sealed double-glazed unit into your existing sash, so the joinery stays. Wellington Glass publishes $800–1,200 per timber window, against $550–850 for aluminium (checked 15 Sep 2026). It is the standard answer for a villa or bungalow you want to keep looking like one.
Why timber is its own job
A single-glazed timber sash was built around a 3–4mm pane. A sealed unit is thicker and heavier, so the rebate has to be prepared to take it and the sash has to be able to carry it. That is bench work, and it is why timber sits above aluminium on every published per-window band.
What stays, and what changes
- Stays: the frame, the sash, the glazing bars, the sill profile, the way the window sits in the wall, and the look from the street.
- Changes: the glass, the beading, and the weight of the sash. Sometimes the hardware, so it still holds and closes properly.
- Does not change: the frame as a heat path. Retrofit improves the glass; the timber is still timber. Only replacement gives you a new, thermally broken frame.
Which timber windows suit it
- Sound, painted or stained timber with no soft spots at the sill or the bottom rail.
- Sashes deep enough in the rebate to hold a thicker unit once it is prepared.
- Casements, double-hungs and fixed lights all retrofit; the hardware question is bigger on double-hungs, because of the weights.
- Not suitable: soft or rotten timber, sashes that have swelled out of shape, or joinery already scheduled for replacement.
The heritage question
Retrofit is often the option that keeps a character house looking right, because the original joinery survives. Whether your particular house sits inside a heritage or character overlay is a district-plan matter, and your council is the one to ask. We will not tell you your street is in a heritage zone; we do not have that data and would not guess it.
What it costs on a whole house
CheckMyBuilder puts most New Zealand retrofit jobs at $10,000–25,000 with a typical job around $16,000, and a typical Auckland job at $18,000. A villa with a lot of small timber sashes tends toward the upper part of a range, because the per-window floor bites on every one of them. The calculator applies that floor rather than hiding it.
Timber retrofit questions
How much does it cost to double glaze timber windows?
$800–1,200 per window for a timber retrofit (Wellington Glass, checked 15 Sep 2026), against $550–850 for aluminium. On an area basis both sit in the $450–800 per m² retrofit band (CheckMyBuilder); the per-window figure is what actually applies to a small sash.
Why does timber cost more than aluminium?
Workshop time. A timber sash usually comes out, goes to a bench, has its rebate prepared for a thicker unit, is reglazed and rebeaded, then goes back and gets rehung. Aluminium is generally a faster process.
Will it change how my villa looks?
From the street, very little: the sash, the profiles and the glazing bars are the character, and they stay. Up close the glass sits deeper and the beading is new. Full replacement is the option that changes the look.
What if the timber is rotten?
Then it needs repair or replacement first, and the honest answer may be that the window should be replaced rather than retrofitted. Frame and sill repairs are not in our estimate and are quoted separately after the measure.
Will the sashes still open?
They should, but a sealed unit is heavier than a single pane. Sash cords, weights, hinges and stays sometimes need work, and that is priced at the measure rather than discovered on the day.
Do I need consent, or heritage approval?
Building consent is usually not needed under Schedule 1 Exemption 8. Heritage and character controls are a separate, district-plan question and your council answers it. We flag anything we spot at the measure but we are not your council.
Can you do leadlights or coloured glass?
That is a specific question for a specific glazier and we won't answer it generically. Ask at the measure; the answer goes in your written quote or it does not go anywhere.