Window Condensation Solutions in Wellington

Condensation forms when warm moist indoor air meets a surface below its dew point. In practice that means the coldest surface in the room, which in most New Zealand homes is single glazed glass or a bare aluminium frame. Wellington makes it worse because the city is both damp and windy, so people close everything up. The result is wet sills, black mould in the reveal corners and curtains that smell.

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 older villas with no subfloor ventilation a share of it comes 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.

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