Condensation in the bedroom
Bedrooms are where most UK condensation complaints start. You spend eight hours breathing out moisture, the door is often shut, the heating is down, and by the coldest part of the night the windows and outside walls are at their coldest.
What happens overnight
A sleeping adult breathes and perspires out roughly 40 grams of water an hour. Two people over eight hours add about half a litre to a room that might hold only 30 cubic metres of air. With the door shut and the trickle vents closed, there's nowhere for that moisture to go.
At the same time, the room cools. Heating often switches off at night, and outdoor temperatures fall to their lowest just before dawn. Glass, window reveals and outside wall corners follow them down. By early morning, the room air is at its wettest and the surfaces are at their coldest — so that's when you see condensation.
Signs to look for
- Water on the inside of the glass, pooling on the sill, every cold morning.
- Black spots on window seals, reveals and the top corners of outside walls.
- Mould on the wall behind a wardrobe or headboard, or on stored items.
- A musty smell, damp-feeling bedding or clothes in wardrobes on outside walls.
If moisture is between the panes of double glazing, that's a failed sealed unit, not bedroom humidity — see window condensation.
Fixes that work
1. Let the room breathe
- Open the trickle vents and leave them open. They're designed to ventilate without a draught.
- Leave the door slightly open if you can. It lets moisture spread through the house and lets warmer air in, so the bedroom isn't the only place it collects. (Close it if a bathroom or drying laundry is next door.)
- Air the room in the morning: open the window wide for 5–10 minutes after getting up, rather than a crack all night if that leaves the room very cold.
2. Keep surfaces warmer
- Move the bed, wardrobe and chests 5–10 cm off outside walls. Free, and often the single biggest help for mould behind furniture.
- Keep a little heat on overnight in very cold weather (a low thermostat setting rather than off) so walls and glass don't drop as far.
- Don't trap the window: heavy curtains drawn tight against the glass make the window colder and the trapped air wetter. Leave a gap at the top or bottom, or use a blind set back from the glass.
3. Remove extra moisture
- Don't dry laundry in the bedroom — each load adds around 1.5–2.5 litres. See drying clothes indoors.
- A small dehumidifier on a timer overnight can work well. Compressor models lose capacity in cold rooms; check real running costs and extraction.
- Wipe condensation from glass and sills each morning so it doesn't soak into frames and plaster.
Why the bedroom and not the rest of the house?
Bedrooms are often on the coldest side of the house, unheated during the day, with doors shut and the most people in the smallest volume for the longest time. North-facing bedrooms get no sun to dry them. Bedrooms over garages or under poorly insulated roofs add more cold surfaces. Our thermal bridges guide explains why corners and the wall–ceiling line are worst.
Check your bedroom
A hygrometer by the bed for a week will show how high humidity gets overnight. Enter your readings in the full assessment to see which surfaces cross the condensation and mould thresholds, and which change makes the most difference.