The downsides of double glazing in older Wellington houses
The disadvantages of double glazing start with the cost, and with what new glass on its own doesn't fix. A draughty sash can stay draughty, and a standard aluminium window still rates lowest for keeping heat in. Standard double glazed units also do relatively poorly against aircraft noise. Go through them before anyone quotes on double glazing an older house in Wellington.
How much each one matters depends on the house. Several of them also change what the quote needs to include.
The downsides, one at a time
Price per glass unit
On a Wellington glazing firm's price list from February 2026, retrofit work is charged per glass unit, so the more units a job has, the more it costs. National figures put a whole three-bedroom retrofit at $10,000–25,000, and GST isn't stated in those.
Draughts around old sashes
A draughty old sash lets air in through the gaps around it rather than the glass, so check the quote for new seals, whichever way of retrofitting Wellington windows with double glazing suits your frames.
Cold aluminium frames
With standard double glazing, an aluminium window rates R0.24 in MBIE's R-value table, lower than thermally broken aluminium, uPVC or timber. Standard aluminium frames can still get condensation after the new glass goes in. There's more about condensation on double glazed windows.
Heritage rules
In Wellington City, a listed heritage building, a house in a heritage area or one in a Character Precinct can need resource consent before its windows change. Check the rules for double glazing timber sashes and casements in Wellington before you order.
The wait
Forum posts from 2017 to 2024 describe waits of several months, first for a measure and then for manufacture. Ask how long each step is taking now.
Draughts and cold frames are worth a line in your enquiry, so a local installer knows about them before following up.
Ask for a quoteHow long the heating season runs, in the city and inland
Double glazing cuts the heat lost through windows, so it counts for more in a house that needs heating for more of the year. Wellington sits between Auckland and Christchurch on that.
Winter nights at Kelburn are close to Auckland's, with a July average low of 6.7°C against 7.7°C. Cooler summers stretch the season instead. Kelburn's January days average a high of 20.3°C, against 23.9°C in Auckland. By our arithmetic, more of Kelburn's extra heating need over Auckland falls between November and March than between June and August, though most of Kelburn's own heating is still needed from April to October.
Across the region, heating need is lower on the coast and higher inland. At Wallaceville in Upper Hutt and East Taratahi near Masterton, it comes close to Christchurch's. There's no station figure for Lower Hutt or Porirua.
Windows aren't the only way heat escapes, so the order of jobs matters. Up to 40% of a poorly insulated home's heating energy can be lost through its windows, according to EECA, and with double glazing the share drops to 25% or less. If the ceiling and underfloor aren't insulated yet, start there. Warmer Kiwi Homes helps eligible owner-occupiers pay for that insulation, but not for windows.
Heating need at Kelburn
About four-fifths
of Christchurch's
Well over one and a half times Auckland's
Our arithmetic, from NIWA heating degree days measured the same way in all three cities.
Aircraft and road noise, and what to check first
Wellington Airport's glazing fact sheet (February 2016) says standard double glazed units perform relatively poorly at 125–250 Hz, where aircraft noise dominates. The same sheet describes acoustic laminated glass.
If it's road or rail noise that bothers you, tell the installer before they measure. Ask for the glass to be named in the quote, along with what it's meant to do about the noise.
Wellington Airport's Quieter Homes programme
If your home is inside Wellington Airport's Air Noise Boundary and was built before 22 March 2012, it may be covered by the airport's Quieter Homes programme, which pays 75% or all of a noise package for eligible homes.
The airport works through the area in stages and contacts owners when their turn comes. It decides what each house gets. Every package includes mechanical ventilation, and not every house gets new glass.
If you're near the airport and thinking about windows for aircraft noise, check whether your home is inside the Air Noise Boundary before paying for glass yourself.
Is double glazing better than it was 20 years ago?
High-performance glass rates higher than standard double glazing, taking an aluminium window from R0.24 to R0.35. In the fifth edition of MBIE's H1 guidance, the window R-value for new Wellington housing rose to R0.46 for building consent applications from 1 May 2023.
That's a benchmark for designing new homes, not a rule the windows in an existing house have to meet.
What Healthy Homes requires of rentals
Nothing in the Healthy Homes standards requires double glazing. They do require draught stopping, which means no unreasonable gaps, windows included, and a house's age is no excuse. The deadline for private rentals to comply was 1 July 2025.
That matters in Wellington City, where 41% of households don't own the home they live in. Among New Zealand's cities and districts, only Hamilton has lower home ownership.
A landlord with draughty sashes has to deal with the gaps, whether or not the glass changes.
For a rental, say roughly how many flats and windows there are when you ask, so the quote can take in the whole property.
Ask for a quoteCheaper steps before windows
If new windows are a while off, close the curtains before dark. By EECA's figures, that saves $80–90 a year.
Window film kits are another low-cost option EECA mentions, but a kit lasts about a season, and the film won't stick to aluminium.
Households with a SuperGold Combo Card or a Community Services Card can ask the Wellington Curtain Bank about free lined curtains. When it's time to pay for the windows themselves, read about borrowing to double glaze in Wellington.
Other questions on the drawbacks
What are the downsides of double glazing?
There's the cost, to start with, and one Wellington firm's published retrofit prices run per glass unit, so every pane adds to the bill. New glass also leaves draughty gaps and standard aluminium frames as they were, and standard double glazed units are relatively weak against aircraft noise. In Wellington City, heritage and Character Precinct rules can mean a resource consent as well.
Is there a 25% glazing rule?
We couldn't find a New Zealand source for one. The 2007 schedule method for new homes applied only where windows made up no more than 30% of the wall area, and the sixth edition of MBIE's H1 guidance, in use since November 2025, caps wall glazing at 40% for its calculation method. Both apply to new homes and additions, not to the windows a house already has.
Is it worth double glazing an older Wellington house?
It depends on the house. Heating need is higher here than in Auckland, so keeping heat in counts for more, but the case is weaker while the ceiling and underfloor are uninsulated, or if the quote leaves the draughty gaps alone.
Does Wellington Airport pay for double glazing?
Through its Quieter Homes programme, the airport covers 75% or all of a noise package for eligible homes inside its Air Noise Boundary. The programme is about noise rather than warmth, and not every house gets new glass.
Do landlords have to double glaze a rental?
No. Healthy Homes doesn't require double glazing, though a landlord still has to stop draughts coming through unreasonable gaps, and that includes gaps around the windows.
Before you decide, ask about your own windows
In the form's "Anything else" box, tell us which of these downsides worries you most, and we'll pass your enquiry on to a local installer.