Why mould grows in winter (and how to stop it)
Cold surfaces turn indoor moisture into water
Mould grows in winter because walls and windows get cold while the air inside stays warm and moist. Warm air can hold more water vapour than cold air. When it touches a surface colder than itself, it cools, can no longer hold all that vapour, and leaves the excess behind as water. That film of condensation on a wall or window frame is all mould needs, and in winter it can form every night and never fully dry.
Summer air carries plenty of moisture too, but walls are warm, windows are open and surfaces dry quickly. Take away the cold surface and the problem largely goes, which is why so much mould seems to arrive with the first cold spell.
Why Cyprus homes are caught out
Many homes on the island are designed to stay cool. Concrete, tiled floors and little or no wall insulation work well in August, but in January those same walls get cold and stay cold. Plenty of homes have no central heating, so one or two rooms are warmed while the rest are left chilly, and moist air from the warm rooms drifts into the cold ones and condenses there. This is a common reason one room is always the mouldy one.
The way homes are heated adds to it. Portable gas heaters give off water vapour as they burn, so they warm the room and dampen it at the same time. An air-conditioner on its heating setting warms the air without taking much moisture out, and a room heated this way is usually kept sealed. North-facing rooms that get no winter sun, and ground-floor flats with cold floors, tend to suffer most.
Winter habits that add moisture
- Windows kept shut day and night to hold in the heat.
- Washing dried on airers indoors because it won't dry outside (see the hidden cost of indoor drying).
- Longer hot showers and more cooking, often with the extractor left off because it pulls in cold air.
- Wardrobes, beds and sofas pushed tight against outside walls, leaving cold, still pockets behind them where the backs of furniture start to spot.
Where winter mould usually starts
Look first at the top corners of outside walls, where ceiling meets wall, and at window reveals and sills. Then check behind furniture on outside walls, inside built-in wardrobes, and along the skirting in ground-floor rooms. Bedrooms are often hit hardest, because a closed door and a night of breathing load a small room with moisture; bedroom mould has its own guide.
Stopping it this winter
The aim is warmer surfaces and drier air. Heat the home as evenly as you can, rather than one room hot and the rest cold, and keep doors shut between warm and cold rooms. Air each room briefly every day; the piece on airing in cold weather explains why a few minutes wide open beats a window left on the latch. If you use a gas heater, let some fresh air into the room while it burns. Pull furniture a little away from outside walls, wipe wet windows each morning, and put a dehumidifier in the room that struggles most.
Small surface spots can be cleaned with a mould cleaner and a damp cloth, wearing gloves and a mask, and then dried fully. Don't paint over them, because the growth comes back through.
When it returns every winter
Mould that reappears in the same place each year usually points to a cold spot in the structure, or a second moisture source working alongside the condensation. Finding the source of the water is step one, so the mould has nothing to come back to. A check of the cold walls and corners takes moisture readings in every affected room and ends with a room-by-room moisture map sent to your phone. Typical fixes include insulating the cold spot, upgrading the extractor and finishing in an anti-mould coating. Homes that struggle every year can also use a plan with a monthly visit that keeps humidity down and catches regrowth early.
Mould back again this winter? book an inspection from €75 or call +357 99 759144.