Damp, mould & air
Waking up to wet windows? Fix condensation
If you wake to streaming glass every morning from October onwards, your windows are reporting on last night’s air. Condensation is the most common damp problem in UK homes and the one most likely to be solved with habits rather than spending.
By the Tickover team · Published 11 May 2026 · 3 min read
The physics, briefly
Warm air holds water as invisible vapour, and the warmer it is, the more it can hold. Overnight the glass becomes the coldest surface in the room, the thin layer of air touching it cools past its dew point, and the vapour turns back into water. The windows are not the fault; they are the messenger.
Make less moisture
A household breathes, cooks and showers roughly 10 to 14 litres of water into its own air every day. You cannot stop breathing. You can put lids on pans, shut the bathroom door with the extractor fan running, and be deliberate about drying washing indoors, which adds a couple of litres per load.
Move more air
Ventilation is a trade of a little warmth for a lot of dryness, and it is a good trade. Trickle vents (the small slots at the top of modern frames) exist for exactly this: open them and leave them open. Then add a purge: ten to fifteen minutes of windows properly open each morning swaps the damp overnight air for fresh air the heating warms through the day.
Heating pattern matters too. Long, low background warmth keeps wall and glass surfaces above the dew point, while short fierce blasts leave surfaces cold and load warm air with moisture. In a home that struggles with condensation, steady and modest usually beats brief and tropical.
The morning routine
- Squeegee or towel the glass; wring out into the sink, not the radiator
- Open bedroom windows wide for ten minutes while the kettle goes on
- Leave trickle vents open all day; they are there for this
- Lids on pans and the extractor on every time you cook
- Bathroom: fan on, door shut, until the mirror clears
- Keep wardrobes and beds an inch or two off cold outside walls
40–60%
relative humidity to hold indoors
10–14L
moisture a household adds daily
15 min
morning purge to reset a bedroom’s air
The condensation year
- Heating back on: open trickle vents
- Wipe-and-vent season every morning
- Purge ventilate 10–15 minutes daily
- Wash down any mould that crept in
- Air the whole house on dry days
The dehumidifier question
A dehumidifier is a tool, not a cure. It earns its keep while washing dries in a closed room, in bedrooms that cannot be ventilated (a loud road, a ground-floor security worry), and through the coldest months while new habits bed in. If it takes one running in every room to keep mould away, the house has a moisture or ventilation problem that wants diagnosing, not drowning out.
Two things condensation is not. Mist sitting between the two panes that never wipes away is a failed sealed unit: see misted double glazing. And black speckles already growing on frames or reveals need cleaning off safely before they settle in for the winter.
Not sure what you’re dealing with?
Not sure whether it is condensation or something in the fabric of the building? Self-Diagnose in the Tickover app narrows it down in a few minutes and tells you who, if anyone, you need.
Quick answers
Why do my windows stream in the morning?
Overnight the heating goes off, surfaces cool, and the moisture from evening showers, cooking and eight hours of breathing has nowhere to go. Glass cools fastest, so the room’s vapour condenses there first. It is a sign of damp, still air rather than a fault with the windows, and bedrooms with closed doors and no vents suffer most.
Should I leave a window open at night in winter?
A trickle vent open, or a window on its night latch, makes a real difference to bedroom condensation, and leaving the bedroom door ajar helps air move too. If noise or security rules that out, purge the room for ten to fifteen minutes each morning and consider a small dehumidifier for the coldest months instead.
Do dehumidifiers stop condensation?
They remove moisture from the air, so they reduce condensation while they run, and they are excellent in drying rooms and unventilated bedrooms. They do not fix the reason a home is damp. Treat a dehumidifier as a bridge while habits, extraction and ventilation improve, not as the destination.
Is condensation on windows bad for the house?
Left to sit, yes. Water pools on cills, breaks down paint and sealant, feeds black mould on frames and reveals, and keeps the surrounding plaster cold and damp. Wiped each morning and tackled at source, it is a manageable winter quirk. Mist trapped between the panes is different: that is a failed double-glazing unit.
This guide is general information for UK homes, not advice about your specific property. Anything involving gas must be done by a Gas Safe registered engineer, and notifiable electrical work by a qualified electrician. If you smell gas, call the National Gas Emergency line on 0800 111 999. If you’re ever unsure, stop and get a professional in — that’s exactly what Tickover is for.
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