Yes — double glazing significantly reduces condensation on glass in winter. It works by keeping the inside pane of glass close to room temperature, so moisture in the air has less cold surface to condense on. It won’t fix a ventilation problem on its own, but for most Wellington homes it’s the single most effective step toward drier windows and less mould.
If you’re waking up to wet windows, damp curtains, or black mould creeping along your window sills every winter, you’re not alone. It’s one of the most common complaints we hear from homeowners across the Wellington region and Kapiti Coast between May and September. In this article, we explain why it happens, why single glazing makes it worse, and what upgrading your windows to double glazing can actually do about it.
Why Wellington Homes Get So Much Winter Condensation
Condensation forms when warm, moist indoor air meets a cold surface — most often a window pane. Wellington’s combination of high humidity, sharp overnight temperature drops, and older houses (many built before modern insulation and ventilation standards existed) makes this worse than in many other parts of the country.
A few things ramp up moisture levels inside a typical home without anyone realising it:
- Showers and baths
- Drying clothes indoors
- Cooking without extraction
- Unflued gas heaters
- Closing rooms up, reducing ventilation and airflow, particularly in bedrooms
With single glazing, the temperature of the inside surface of the glass is close to the temperature outside, making it the coldest surface in the room and the first place moisture condensates.
This isn’t unique to any one house. BRANZ notes that as New Zealand homes have become more airtight, condensation and mould have actually increased in many cases — simply because moist air has fewer places to escape.
Why Condensation Is More Than Just Annoying
A bit of fog on the window might seem harmless, but ongoing condensation is usually the first sign of a bigger moisture problem. Left unaddressed, it can lead to:
- Mould growth on sills, frames, curtains, and nearby walls — which can affect respiratory health, particularly in children and the elderly
- Water staining and rot in timber joinery, especially in older wooden window frames common in Wellington villas and bungalows
- Damaged paintwork and wallpaper near windows
- Musty odours that linger throughout the house
- Higher heating bills, since damp air feels colder and takes more energy to warm
The NZ Ministry of Health confirms that damp and mould are proven contributors to poor indoor air quality and chronic health conditions. Mould returning after cleaning is a sign the underlying moisture problem hasn’t been addressed — not a sign of a dirty home. Government building performance guide on mould in damp buildings.
How Double Glazing Reduces Condensation
Double glazing works by sealing two panes of glass together with an insulating air or gas-filled gap between them. Modern high-performance double glazing also includes an invisible coating on the inside of one pane that further reduces heat loss markedly. The combined effect is a reduction in heat loss through the glass, keeping the inside pane much closer to room temperature than a single pane would be.
The result: the inside surface of the glass stays warm enough that indoor moisture has far less opportunity to condense on it. You’ll typically notice:
- Drier windows, even on cold mornings
- Less visible fogging and water on the inside surface of the glass
- A warmer feel to rooms overall, since the window is no longer acting as a cold spot pulling down the room temperature
- Reduced risk of mould and damage to timber frames and furnishings
High-performance SuperTherm™ double glazing can reduce heat loss through windows by up to 81% — meaning better comfort, lower energy bills, and a healthier, drier home environment.
However, it’s important to understand what double glazing does and doesn’t do: it reduces condensation on the glass itself, but it isn’t a complete fix for high indoor moisture levels in a poorly ventilated home. If a home has limited airflow, dries clothes indoors constantly, or has an extraction problem in the bathroom or kitchen, double glazing needs to be paired with improved ventilation for the best result.
Image: Timber single glazed window on left vs an aluminium insert with double glazing on right.
What Else Helps Alongside Double Glazing
If mould and condensation are a recurring issue, double glazing works best as part of a broader approach:
- Ventilate wet areas — run extractor fans ventilated to the outside in bathrooms and kitchens during and after use
- Dry clothes in a well-ventilated space where possible
- Open windows briefly on dry, warmer days to let trapped moisture out
- Check for other cold surfaces — condensation can also appear on uninsulated walls or ceilings, not just glass
- Consider your worst-affected rooms first if you’re retrofitting gradually — bedrooms and living areas that lose the most heat are usually the best place to start
Retrofit or Full Replacement — Which Helps More With Condensation?
It depends on the frame. Both options resolve condensation on the glass itself, but the frame behaves differently depending on what it’s made of.
Retrofitting into standard aluminium frames will reduce condensation on the glass, but because standard aluminium conducts heat readily, you may still see condensation forming on the frames themselves. Retrofitting into timber frames performs better in this respect — timber doesn’t conduct heat the way aluminium does, so the frame stays warmer. If you want to eliminate condensation on both the glass and aluminium frames, replacement of your old aluminium frames with new thermally enhanced (sometimes called “thermally broken”) aluminium joinery is the best option that addresses both, since the thermal break stops the frame itself from becoming a cold surface.
In short:
- Retrofit into standard aluminium frames — resolves condensation on glass but condensation on original aluminium frames may still occur
- Retrofit into timber — condensation resolved on both glass and frames as timber doesn’t conduct heat like aluminium
- Full replacement with thermally enhanced aluminium — condensation resolved on both glass and frame
If you’re not sure which solution is best for your home, our guides on the benefits of retrofit double glazing, aluminium inserts and full aluminium replacement joinery go into more detail on how to choose.
If you’re weighing up whether the investment is worthwhile at all, our guide on double glazing costs and the value they add to your home are worth a read.
Frequently Asked Questions
Does double glazing completely stop condensation on the inside of my windows?
The effectiveness of double glazing at reducing condensation depends on the levels of indoor moisture and ventilation, and the type of joinery in your home. In dry, well-ventilated homes, particularly those with timber joinery, condensation is almost entirely gone. Homes with older aluminium frames may still have condensation on the frames and glass closely adjoining the frames when humidity is high. Best results occur when double glazing is paired with good ventilation and moisture control.
Does double glazing stop condensation on the outside of my windows?
Condensation on the outside of double glazing means your windows are working correctly. It shows that the glass is effectively trapping heat inside your home, leaving the exterior pane cold enough for morning dew to form. It typically occurs on clear, still, humid nights or early mornings when the temperature of the outer glass drops below the dew point, and disappears as soon as the outside temperature or breeze increases. This is completely normal.
Why does my house get mould even though I clean it regularly?
Mould keeps returning because cleaning treats the symptom, not the cause. The underlying issue is usually excess moisture and a lack of airflow or heating. Until that’s addressed, mould will keep reappearing even after a thorough clean.
Does retrofit double glazing help as much as full replacement?
Double glazing resolves condensation on the glass either way, but the frame itself behaves differently. Retrofitting into timber performs well, since timber doesn’t conduct heat like aluminium. Retrofitting into older aluminium frames can still be associated with condensation on the original frames. If you want condensation resolved on both glass and aluminium frames, full replacement with thermally enhanced aluminium joinery is the option that addresses both.
Which rooms should I prioritise?
Bedrooms and main living areas that lose the most heat overnight are usually the best place to start — these are where condensation tends to be worst and where the health impact of mould is most significant.
Talk to Wellington Glass and Mirror
If your windows are fogging up every morning or you’ve noticed mould starting to take hold, we’re happy to talk you through whether retrofit or full replacement double glazing makes the most sense for your home. As a Licensed RetroGLAZE® Partner, we specialise in both options for timber and aluminium-framed windows and doors across the wider Wellington region and Kapiti Coast.
No obligation — just straightforward advice from people who know glass.