Damp is the quiet epidemic of city renting. It shows up as a musty smell, a black bloom in the bathroom corner, condensation streaming down a single-glazed window on a cold morning. It’s bad for the building and worse for airways, and in a small flat it spreads fast. The good news: most of it comes down to moisture you can control.
Where the water comes from
In a sealed apartment, you are the main source of humidity — breathing, showering, cooking, drying laundry indoors. A single load of wet washing dried on a rack can release litres of water into the air over a day. That moisture has to go somewhere, and in a cold flat it condenses on the coldest surface it can find: window glass, an exterior wall, the back of a wardrobe.
The comfortable, mould-resistant range
Relative humidity in the rough range of forty to sixty percent is the sweet spot — comfortable to breathe and hostile to mould, which thrives above that. A cheap hygrometer the size of a coaster tells you where you stand. If you’re regularly above sixty, you have a ventilation problem, not a cleaning problem.
- Vent the steam at the source — bathroom fan on during and after a shower, kitchen extractor while cooking.
- Dry laundry with a window open or, ideally, not indoors at all.
- Leave a gap behind furniture on cold external walls so air can move and surfaces stay warmer.
- Heat gently and steadily rather than in cold-then-blast cycles, which drive condensation.
You can scrub mould off a wall a hundred times. Until you fix the moisture, it comes back every time.
When it’s already there
Small patches of surface mould on a hard surface can be cleaned and the area kept dry and ventilated to stop it returning. But mould is a symptom. If it keeps coming back, or covers a large area, or you smell it without seeing it, that points to a moisture source — a leak, a cold bridge, chronic under-ventilation — that needs addressing, sometimes by the landlord.
Know when it’s not yours to fix
Renters often blame themselves for damp that’s structural — a failed seal, rising moisture, inadequate building ventilation. If you’re managing your own moisture sensibly and still fighting it, document the conditions and raise it with whoever’s responsible for the building. A healthy home is partly your habits and partly the fabric around you.