Window Condensation Solutions in Dunedin – Ventilation, Thermal Breaks & Low E Upgrades

Condensation forms when warm moist indoor air meets a surface below its dew point, and the coldest surface in most homes is single glazed glass or a bare aluminium frame. This city makes it worse than most. NIWA's 1991 to 2020 averages put Dunedin at roughly 50 days of ground frost a year, about 15 of them in July, and much of the older housing has no mechanical extraction at all.

Glass, frame or air: which one is yours

If the water sits on the glass, the glass is the cold surface and double glazing fixes most of it. If the glass is dry but the aluminium frame is running with water, the frame is the cold bridge and only a thermally broken frame or an insulating liner will fix it.

If both are wet in every room, the moisture load in the house is too high, and no amount of glass will fix that on its own. Unflued gas heaters, drying washing indoors and unextracted showers put litres of water into the air every day.

What double glazing does to it

A double glazed unit keeps the inner pane much closer to room temperature, so the dew point is rarely reached on the glass. Retrofitting into existing frames costs roughly half of full replacement and gets you most of that benefit.

What it does not do is warm the aluminium frame. Plenty of homes retrofit their glass and then find water still forming on the frames, which surprises people who were not told. We tell you up front.

Ventilation, and the rule for rentals

Moist air has to leave the building. That means extraction that vents outside and not into the roof space, and openable windows that get used. The Healthy Homes ventilation standard requires each habitable room in a rental to have openable windows, doors or skylights totalling at least 5 percent of the floor area, and kitchens and bathrooms to have extractor fans ducted outside.

Indoor relative humidity below about 60 percent keeps mould and dust mites in check. A cheap hygrometer will tell you where you sit, and it is worth knowing before you spend thousands on glass.

Working out which of the three you have

A hygrometer costs less than a callout

Indoor relative humidity below about 60 percent keeps condensation, mould and dust mites in check. A cheap hygrometer left in the worst room for a week tells you whether you have a moisture problem or a cold surface problem.

It is worth knowing before you spend thousands on glass, because the two need completely different answers and only one of them involves us.

Where the moisture is coming from

Unflued gas heating, drying washing indoors, showers without ducted extraction and cooking without a rangehood each put litres of water into the air every day. So does a wet subfloor.

In the low lying southern suburbs the groundwater can sit within 30cm of the surface, so a share of it is coming up through the floor rather than out of the air. Fixing the source is cheaper than fixing the symptom, and in most houses it is a fan that vents into the roof space rather than outside.

How Window and Glass Repair Dunedin delivers window condensation solutions in Dunedin

Dunedin is the hardest thermal environment in the country for windows, and it is the one place where the wrong specification is genuinely expensive over time.

1. Assess the room, not just the window

   How the room is heated, ventilated and used decides as much about the outcome as the glass does. Upgrading glazing in an unventilated bedroom moves the condensation to the frame edges rather than removing it.

2. Establish the requirement that applies

   Dunedin is H1 climate zone 5, the highest window performance requirement in New Zealand. Window and Glass Repair Dunedin confirms whether your work is consented and therefore has to meet it, or a like for like replacement that does not, because the two lead to very different products.

3. Measure and record what exists

   Opening sizes, room floor areas, existing glass type and frame construction. On compliance work that record is the evidence behind the statement you make to a tenant or to council.

4. Specify the unit deliberately

   Glass thickness, cavity width, low emissivity coating, argon fill and spacer type all get chosen for the orientation and the exposure rather than sold as a package. Window and Glass Repair Dunedin explains what each component does.

5. Be honest about the frame

   Retrofitting a sealed unit into a standard aluminium frame improves the glass and leaves the frame conducting. In a city with fifty frost days a year that frame will still sweat, and Window and Glass Repair Dunedin says so before quoting rather than after.

6. Manufacture and install

   Units are made to the measured openings, so there is a lead time and nothing is adjusted on the day. Installation includes new tape, new beads and clearing the rebate drainage.

7. Verify, document and hand over

   Every sash checked to operate and to fix open, then a written record of what was installed where. On a rental that document is what supports compliance if it is ever questioned.

What window condensation solutions is worth in a Dunedin home

The case here is stronger than anywhere else in the country and the numbers are worth knowing.

The highest requirement zone in New Zealand

Climate zone 5 carries the country's highest window performance requirement because heat loss here is greater. A specification that satisfies a warmer city does not satisfy this one, which is why comparing a Dunedin quote to a friend's Auckland quote is misleading.

Retrofit is usually the best value route

Around $450 to $800 per square metre of glass, or roughly $550 to $850 per aluminium window and $800 to $1,250 for timber. A whole house commonly lands between $10,000 and $24,000, and the existing frames and finish stay.

Do the rooms you use, first

Bedrooms and living areas on the cold elevation return most of the benefit. Small hallway and toilet windows return the least and are worth doing last, or not at all.

Cold housing is under real scrutiny here

MBIE inspected fifty three Dunedin student rentals across May and June 2026. Whatever your view of the rules, the direction is clear, and upgrading ahead of enforcement is cheaper than upgrading during it.

What window condensation solutions costs in Dunedin

Thermal work here has a stronger case than anywhere else in New Zealand, and the numbers are worth seeing before the sales pitch.

Retrofit double glazing

Roughly $450 to $800 per square metre of glass, or about $550 to $850 per aluminium window and $800 to $1,250 for timber. A whole house commonly lands between $10,000 and $24,000 with the existing frames and internal finishes untouched.

Sealed unit upgrades

A low emissivity coating, an argon fill and a warm edge spacer add very little to a unit being made anyway. In climate zone 5 they are close to free performance, and retrofitting them later means paying for the unit twice.

New thermally broken joinery

Meaningfully more per window than standard aluminium and it is the only route that removes the cold bridge through the frame entirely. On consented work in this zone it is effectively the requirement rather than an upgrade.

Compliance work on a rental

Most Healthy Homes ventilation failures are hardware rather than glazing. Freeing painted shut sashes, replacing seized stays and fitting working catches usually brings a house into compliance for a fraction of what owners expect.

Where to spend it in a Dunedin home

The same budget produces very different outcomes depending on where it goes.

Bedrooms and living rooms on the cold elevation

These return most of the comfort benefit and most of the condensation reduction. Small hallway and toilet windows return the least and are worth doing last or not at all.

Extraction before glazing, every time

A vented range hood and a ducted bathroom extractor remove moisture where it is produced. This is the cheapest intervention available and it is frequently the only one needed. Upgrading glazing in an unventilated house moves the condensation rather than removing it.

The frame is the limit on a retrofit

Retrofitting a sealed unit into a standard aluminium frame improves the glass and leaves the frame conducting. With fifty frost days a year that frame will still sweat at the edges, and anyone who does not tell you this before quoting is selling rather than advising.

Stage it by room, not by elevation

Doing the rooms people actually use gets you most of the benefit for part of the spend. Doing it by elevation looks tidier from the street and delivers less.

Why Dunedin windows run with water

Condensation is a symptom of three things interacting, and treating only one of them rarely works.

Moisture being produced indoors

Cooking, showering, drying clothes inside and unflued gas heating all add litres of water to the air every day. A household of four can produce a surprising volume before anyone opens a window.

Cold surfaces for it to condense on

Single glazing and non thermally broken aluminium frames are the coldest surfaces in a room, so that is where the moisture lands first. The window is the messenger.

Not enough air changes

Without extraction and ventilation the moisture has nowhere to go. Sealing a draughty house without adding ventilation makes condensation worse rather than better.

What actually fixes it in a Dunedin home

In rough order of cost and effectiveness, and some of it is not glazing work at all.

Extraction at the source

A vented range hood and a bathroom extractor ducted outside remove moisture where it is made. This is the cheapest intervention and it is frequently the only one needed.

Thermal upgrade to the glazing

Retrofit double glazing raises the internal glass temperature so moisture stops condensing on it. Where the frames are standard aluminium, the frame edges can still sweat and we say so before quoting.

Thermally broken frames on new joinery

Where joinery is being replaced anyway, a thermal break in the frame removes the last cold bridge. It is the complete solution and it only makes sense when the frames are going regardless.

Window Condensation Solutions at a glance

Water on the glass

Retrofit double glazing or replacement units

Water on the frame

Thermally broken joinery, or accept some frame condensation

Water everywhere

Moisture load and ventilation, before any glazing spend

Target humidity

Below about 60 percent relative humidity indoors

Rental rule

Openable area at least 5 percent of floor area, plus ducted extraction

Mould

Treated at the reveal once the cause is fixed, not before