21/10/2026
Wet windows are a ventilation problem.
Condensation on the glass means the air inside your home is holding more moisture than the house can shed. Cooking, showering, drying laundry indoors and simply breathing put several litres of water into a typical home every day. It has to go somewhere — and if it isn't extracted, it ends up in your linings, your curtains and your lungs.
The 2023 Census found 18% of occupied homes were damp at least some of the time, and one in seven had mould larger than an A4 sheet. That isn't bad luck. It's a design outcome.
Clause G4 can be satisfied with openable windows totalling 5% of floor area — which assumes someone opens them, wide enough, often enough, through a cold winter. Compliance is not the same as performance.
What actually works:
→ Extraction at the source — bathrooms, kitchens and laundries ducted to outside, properly sized, on a run-on timer or humidity sensor
→ Make-up air from outdoors, not the roof space or the garage
→ Balanced ventilation with heat recovery for airtight new builds and deep retrofits, so fresh air doesn't cost you the heat you've paid for
And the part that gets missed: ventilation is an early design decision, not a late one. Unit locations, duct routes, external grilles and acoustic separation need space reserved before linings go on. Retrofitted afterwards, the compromises show — in noise, in performance, and in your ceiling.
Airtightness, insulation and ventilation are one system. Get one wrong, and the other two suffer.
Planning a new home, a retrofit or a multi-unit development? Let's talk about the ventilation strategy early.
Full insight link in the comments.
