💧 Water & Weather
Condensation on Windows: What It Tells You About Your Home
Wet windows on a cold morning are a humidity problem, not a window problem — unless the moisture is between the panes.
Marcus Ibe · Oct 21, 2026 · 5 min read · 5 steps
Condensation forms when warm, moist air meets a cold surface. In winter, windows are usually the coldest surfaces in the room, so they show the problem first.
Left alone, it leads to black mould on frames, peeling paint, and rot in wooden sills.
Where the moisture is matters
Condensation on the inside of the glass means indoor air is too humid. On the outside, it is harmless and actually a sign of well-insulated glazing. Between the panes of double glazing, it means the sealed unit has failed and needs replacing — the frame can usually stay.
Where indoor moisture comes from
An average household releases litres of water vapour into the air every day from breathing, cooking, showers, and drying clothes. Without ventilation, it has nowhere to go.
Reduce it
- Use extractor fans when cooking and showering, and leave them on for 15 minutes afterwards
- Put lids on pans
- Dry clothes outside or in a vented dryer where possible
- Open trickle vents at the top of windows, or crack a window briefly each morning
- Keep heating at a steady low level rather than letting rooms get very cold
- Move furniture a few centimetres away from external walls
Measure humidity
A cheap hygrometer tells you what is going on. Indoor relative humidity of roughly 40 to 60 percent is comfortable. If it stays above 60 percent despite ventilation, a dehumidifier helps, and persistent damp may point to a leak or rising damp worth investigating.
Clean mould promptly
Wipe mould from frames and seals with a mould-removal product or a mild detergent solution, wearing gloves. Dry the area thoroughly. Repeated mould in the same place is a sign the underlying humidity has not been solved.
This is general home-maintenance information, not professional advice. Building codes, permits, and safe practices vary by location — consult a licensed contractor, electrician, or plumber for work beyond your experience.