💧 Water & Weather
Why Bedrooms Get Mould and How to Stop It
Breathing overnight releases moisture into cool rooms. Ventilation and steady warmth are the cure.
Marcus Ibe · Oct 1, 2026 · 6 min read · 4 steps
Black spots on bedroom walls, behind wardrobes, and around windows are a common winter problem. Bedrooms are often kept cooler than living spaces, and people breathe out a surprising amount of moisture overnight.
That moisture condenses on the coldest surfaces, where mould grows.
Why it happens
Two adults sleeping can release a noticeable amount of water vapour in a night. If the room is closed up and cool, humidity rises and moisture settles on external walls and windows. Furniture pushed against outside walls stops air circulating, which is why mould often appears behind wardrobes and beds.
Simple fixes
- Open a window slightly or use trickle vents overnight
- Keep the bedroom gently heated rather than cold
- Move furniture a few centimetres away from external walls
- Do not dry clothes on bedroom radiators
- Open curtains and air the room each morning
Cleaning existing mould
Small patches can be cleaned with a mould remover or a mild detergent solution, wearing gloves and a mask and keeping the room ventilated. Do not brush or vacuum dry mould, which spreads spores. Large areas, or mould that keeps returning, point to an underlying problem worth investigating.
Longer-term options
A dehumidifier can help in persistently damp rooms. Improving insulation on cold external walls, upgrading windows, and installing mechanical ventilation are bigger projects that tackle the cause. If you rent, report persistent mould to your landlord in writing.
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.