Condensation and ventilation fixes
Most mould in Scottish homes comes from condensation. Cleaning it off without changing the conditions is why it's back by February.
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Why it happens
Warm air holds more water than cold air. When moist air from a kettle, a shower or a clothes horse hits a cold window or wall, it drops that water as condensation. Do that day after day in a room that's cool and badly ventilated, and mould takes hold.
Three things decide how bad it gets: how much moisture goes into the air, how quickly it's taken out, and how cold the surfaces are. Fixes work on one or more of those.
The usual fixes
Better extraction where the moisture is made
Kitchens and bathrooms should have extractor fans that actually move enough air and vent outside. A lot of older fans are undersized, blocked with fluff, or wired to the light so they stop the moment you leave the room. A humidity-controlled fan with an overrun timer is a common, inexpensive upgrade.
Continuous or whole-house ventilation
Where condensation is in several rooms, a specialist may suggest a continuous low-speed extract fan, or a positive input ventilation unit that brings filtered air into the home from the loft or an outside wall. These are quiet and run all the time on very little electricity.
Trickle vents and air bricks
Windows replaced in the last few decades often have trickle vents, and they're often taped or painted shut. Blocked air bricks under suspended timber floors are another common culprit. Clearing or adding vents costs little.
Warmer surfaces
Insulating a cold ceiling, the reveals around a window, or an uninsulated solid wall raises the surface temperature so moisture doesn't settle there. For stone buildings, insulation needs to suit the wall. Breathable materials matter on older masonry, and in listed buildings or conservation areas you may need consent.
Heating
Keeping rooms at a low, steady background temperature makes condensation less likely than heating hard for an hour and then letting the house go cold. Plenty of councils, including Glasgow and Renfrewshire, suggest keeping rooms above about 15°C in cold weather. Heating costs are a real problem for many households, which is why ventilation and insulation fixes are often the better long-term answer.
Habits that make a difference
- Lids on pans, and the extractor on while cooking.
- Shower with the fan on and the door shut, then leave the fan running for 15–20 minutes.
- Vent tumble dryers outside.
- Leave a gap between furniture and outside walls.
- Don't block vents to stop draughts.
What it costs
A new bathroom or kitchen extractor fan, fitted, is usually one of the cheaper fixes. Positive input ventilation units and insulation cost more. Treating the existing mould is priced separately: see the ranges in our cost guide. If you're not sure condensation is the cause, start with a damp and mould survey.
Common questions
Will a dehumidifier fix condensation?
It helps, especially while drying out a room or a wall. It doesn't fix the underlying balance between moisture, heat and air flow, and running one all the time costs money. Most specialists treat it as a stopgap.
What's a positive input ventilation unit?
A fan, usually fitted in the loft or a cupboard, that pushes filtered air gently into the home. The slight pressure pushes moist air out through gaps and vents. It's often suggested for flats and houses with condensation in several rooms.
Is condensation the landlord's responsibility?
Landlords must keep a rented home free from substantial damp and mould and provide adequate ventilation and heating. Tenants are expected to use what's provided sensibly. Under Awaab's Law in Scotland, the landlord has to investigate any report of damp or mould, whatever is thought to be causing it.
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