Retrofit double glazing for Christchurch homes
Retrofit double glazing keeps your existing frames where they are. The single pane comes out and a sealed double glazed unit goes in. It suits sound aluminium and timber windows, and it's the cheaper of the two routes. Not sure it's right for your house? Double glazed windows in Christchurch covers replacement as well.
Get a quoteWhat retrofit double glazing involves
The beads or putty come off, the old pane is lifted out, and the rebate is checked for depth and drainage. A sealed double glazed unit is made to the measured size, often with low-E glass and argon gas in the gap. The frame is then reworked to hold the thicker glass: routed deeper in timber, or fitted with an adaptor or new bead in aluminium.
The unit is heavier than the pane it replaces, so hinges and stays should be checked against the extra weight. Check your quote includes that. Prices are covered in the double glazing cost guide.
What retrofit double glazing changes in a Christchurch house
Less heat lost through the glass
EECA says a poorly insulated home can lose up to 40% of its heating energy through the windows, and double glazing cuts that to 25% or less. The room holds its heat and the heat pump works less hard.
Much less condensation on the glass
The inner pane stays close to room temperature, so the morning streaming mostly stops. A standard aluminium frame stays cold, so it can still run wet in a hard frost.
Some reduction in outside noise
Consumer NZ notes a noise benefit from double glazing. Laminated glass does more against road noise, so ask for it on street-facing rooms if traffic bothers you.
Which windows can be retrofitted, and which can't
Usually yes
- Aluminium frames with a deep enough rebate
- Sound timber joinery, including villa and bungalow sashes
- Fixed panes and awning windows
Usually no
- Rotten or badly distorted timber
- Very slim older profiles with no room for a unit
- Leadlight and some decorative glazing
If a frame isn't up to it, replace the window rather than forcing a retrofit into it. The aluminium and wooden windows pages go into what an installer looks for in each.
What a Christchurch house usually needs
Start with the year. A home consented after 31 October 2007 was built under rules that effectively required double glazing in the South Island, so if yours is part of the post-quake rebuild, check the glass before you assume it needs doing. Roughly a quarter of the city's homes fall into that group.
Most retrofit work is in the other three quarters. Aluminium joinery from the 1960s through the 1990s is usually a straightforward job if the profile has room for a unit. Villas and bungalows with painted timber sashes take a slim unit with new beads, at a higher price per pane because of the joinery work. Some older homes have been retrofitted already, so a quick look at the edge of the glass, where a sealed unit shows a spacer bar between two panes, saves a wasted call.
Then there's the cold. Christchurch averages about 85 ground-frost days a year, and July nights bottom out around 0.7°C on average, so single glazing here runs wet most winter mornings. That morning condensation is exactly what retrofit fixes.
Glass options in plain English
Low-emissivity coating
An invisible coating that reflects heat back into the room. EECA says low-E can cut the heat lost through a window by up to 30%.
Argon fill
A heavier gas than air in the sealed gap, so less heat moves across it. EECA puts the saving at 5 to 20%. It also recommends a 12 to 16 mm gap and a decent spacer.
Laminated and toughened
Safety glass, needed in doors, low panes and bathrooms under NZS 4223.3. Laminated glass also takes the edge off road noise.
Obscure and patterned
For bathrooms and street-facing rooms, matched as closely as possible to what you have.
When the frames can't take a sealed unit yet
If the frames need work first, the budget won't stretch this winter, or the glass is leadlight, a second pane fitted inside the existing window is the stop-gap. It's cheaper and reversible, but not as warm as a sealed unit.
Retrofit vs new windows vs secondary glazing compares all three, including when secondary glazing is the right call.
Not sure your frames can take it?
Send your frame type and the installer can talk it through when they call.
What happens on the day
The sequence is much the same whoever does it. Someone visits to measure every unit and check each frame, which is when a good installer tells you which windows won't work and why. The units are made to size, so there is a wait between the deposit and the install, and it is longer in winter when installers are busiest. Ask for a realistic date.
On the day, each window is done in turn: old glass out, rebate cleaned and checked, unit in, new beads or seals on, hardware adjusted or replaced. Ask whether the house is done room by room so it's never open to the weather, and what making good is included, since retrofit usually means a little paint at the beads and not much else.
Judging by Christchurch forum threads, people rarely complain about the glass afterwards. The complaints are about gaps, untidy finishing, hardware left as it was, and jobs stopped partway because parts were mis-cut. Every one of those is a question you can ask before you sign, and you have 12 months from completion to report defects under the Building Act.
What retrofit costs
Published NZ installer pricing for 2026 puts retrofit at about $400 to $900 per pane in aluminium and $800 to $1,200 in timber, including GST, or $10,000 to $25,000 for a typical three-bedroom house. The double glazing cost guide explains what moves the price, what a quote should include and why two quotes can be so far apart.
- Retrofit, aluminium frames~$400–900 / pane
- Retrofit, timber frames~$800–1,200 / pane
- Typical 3-bedroom retrofit$10,000–25,000
Published NZ installer pricing, 2026, incl GST
Retrofit double glazing FAQ
What is retrofit double glazing?
Taking the single pane out of an existing window and fitting a sealed double glazed unit in its place, with the frame left where it is. The frame is reworked to hold the thicker glass, either by routing the rebate deeper or with an adaptor or bead system. It is one of three routes EECA lists for an existing house, alongside secondary glazing and full replacement.
Is retrofitting double glazing worth it in NZ?
Where the frames are sound, usually yes. EECA puts window heat loss in a poorly insulated home at up to 40% of heating energy, falling to 25% or less with double glazing, and the inner pane stays warm enough to cut condensation right back. Where the frames are rotten, very slim or draughty, replacement is the better option. Is retrofit double glazing worth it? works through it by situation.
How much does it cost to retrofit double glazing in Christchurch?
About $400 to $900 per pane in aluminium frames and $800 to $1,200 in timber, or $10,000 to $25,000 for a typical three-bedroom house. Published NZ installer pricing, 2026, including GST. The price is per pane, not per window, so a window with one fixed pane and one that opens counts as two. There's a full breakdown of retrofit double glazing cost in the cost guide.
What is the legal requirement for double glazing in NZ?
There is no requirement to double glaze an existing house. New homes in the South Island have effectively needed it since 31 October 2007, when the Building Code's insulation rules went up, and the Healthy Homes Standards for rentals cover draughts around windows but not glazing. If you replace joinery, MBIE's guidance is that the new windows must perform at least as well as the ones removed, without having to meet the full current standard for new builds.
Do I need consent for retrofit double glazing?
Usually not. Work on windows in an existing house of up to two storeys is exempt under Schedule 1, exemption 8 of the Building Act, as long as the window being replaced hasn't failed early (the durability requirement is generally 15 years) and the work doesn't touch a specified system such as sprinklers. The work still has to meet the Building Code, including safety glass rules. Character and heritage areas are a separate planning question: check your property on the Christchurch District Plan maps first.
Will my hinges and stays be upgraded for the heavier glass?
Ask, and get the answer in the quote. A sealed unit weighs more than the single pane it replaces, and several Christchurch homeowners have reported hardware left as it was, with sashes that then dropped or wouldn't stay open. A good quote says which windows get new hinges, stays or sash hardware, and prices it in.
Get a retrofit quote for your house
The installer measures on site and prices each pane.