How to Stop Condensation on Your Windows
26 May 2026 · 6 min read
Wet windowsills and dripping glass every morning are more than an annoyance — left unchecked they cause mould and damage. Here's how to get on top of it.
Why condensation forms on windows
Condensation appears when warm, moist air meets a cold surface — and your window glass is usually the coldest surface in the room. The air can no longer hold the moisture, so it turns to water droplets on the glass. That is why it is worst on cold mornings and in rooms where a lot of moisture is produced, such as kitchens, bathrooms, and bedrooms.
A certain amount is normal in winter. It becomes a problem when it is heavy enough to pool on the sill, soak the frame, or feed mould growth around the window.
Practical ways to reduce it
The goal is to lower indoor humidity and improve airflow. Open windows for a short while each morning, use extractor fans when cooking or showering, keep trickle vents open, and avoid drying washing on radiators. Keeping rooms at a more even temperature also helps, as cold spots are where moisture collects.
Moisture traps and small dehumidifiers can help in particularly damp rooms, and keeping curtains or blinds slightly open overnight lets a little air move across the glass.
When condensation means a failed window
There is one type of condensation you cannot ventilate away: moisture that appears between the two panes of a double-glazed unit, where you cannot wipe it off from either side. That means the sealed unit has failed and is letting moist air inside the glass itself.
This is not a humidity problem — it is a glass problem, and the fix is to replace the sealed unit while keeping your existing frame. It is far cheaper than a whole new window, and a glazier can usually swap the unit in a single short visit.
Why it is worth dealing with
Persistent condensation is not just unsightly. Over time it rots timber frames, blackens seals with mould, and signals that heat is escaping through cold glass. Tackling the cause — and replacing any failed units — protects your home and lowers your heating bills.
If you are not sure whether you have a ventilation issue or a failed unit, a quick look from a glazier will tell you which, and what it would cost to put right.
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