Where the Water Goes: A London Flat Guide to Winter Condensation

By early November, plenty of London flats start showing the same telltale signs: misted sash windows in the morning, a cold patch behind the wardrobe, a faint musty smell in the bathroom. Condensation is not unusual in a UK winter, but London homes have a particular set of challenges. Period conversions, single-glazed windows, small rooms and indoor laundry all add moisture to the air — and then give it nowhere obvious to go.

The good news is that condensation is usually manageable if you interrupt the cycle early. You do not need a laboratory-level understanding of relative humidity. You need a routine, a few checks and a clear idea of what to clean yourself versus what to flag to a landlord.

Why London flats get so damp in winter

A flat produces moisture all day. Showers, cooking, kettle steam and drying laundry are the obvious sources. Less obvious ones include breathing, houseplants and even mopping floors. In a small flat, that water vapour has limited air volume to mix with, so it condenses quickly on the coldest surfaces — often windows, external walls, tiles and the backs of furniture.

Older London conversions can make this worse. Sash windows may be draughty in places but still trap moisture around the frames. Chimney breasts can be cold. Bathrooms are sometimes internal, with no window at all. And in a studio or one-bed flat, the distance between the shower, the drying rack and the bed can be a matter of metres.

Start with a two-minute window routine

Condensation is easiest to deal with when it is still droplets, not staining. Each morning, wipe the inside of windows with a microfibre cloth and wring it out into the sink. Do not push water into the window frame or leave a soggy cloth on the sill. If you have single glazing, this small step makes a real difference over a winter.

Then ventilate. Opening a sash window for five to ten minutes creates a quick air exchange without freezing the whole flat. Do it after showers and cooking especially. If you have trickle vents, check they are open rather than painted shut or blocked by curtains. In shared flats, agree a window routine with housemates so it is not one person’s job every day.

Test the extractor fan rather than trusting it

A noisy bathroom extractor fan is not necessarily a working one. Hold a piece of tissue near the grille while the fan is on. If it stays put, there is some suction. If it droops or falls, the fan may be weak, clogged or ducted badly. Clean the cover regularly and remove lint from the blades where possible. Run the fan during showers and for at least ten to fifteen minutes afterwards.

In kitchens, use the extractor hood every time you boil, fry or steam. If your flat has a recirculating hood rather than one ducted outside, keep the filters clean. A greasy filter will not move air efficiently, and that moisture ends up on your walls instead.

Make indoor laundry less of a moisture bomb

Drying clothes indoors is unavoidable in many London flats, especially in winter. The aim is not to ban it but to control it. Spin laundry as dry as possible before hanging. Put the airer in the bathroom with the extractor fan running and the door closed, or near a slightly open window if the room is well ventilated. Leave space between garments so air can move.

Avoid draping wet washing directly over radiators for hours. It warms the room but releases moisture into the air and can leave walls and curtains damp. A dehumidifier in the same room as the airer can help, but give it room to work and empty the tank regularly.

Give furniture and walls some breathing space

One of the most common condensation traps is a wardrobe or bed pushed flush against an external wall. Cold air meets warm indoor air behind the furniture, and mould can develop where you cannot see it. Pull large items a few centimetres away from the wall. Where possible, leave a gap behind so air can circulate.

Check behind wardrobes, under beds and in corners once a month. If you find a cold, damp patch, clean it and improve airflow before it spreads. Do not block air bricks or vents with boxes, books or bedding.

Use a dehumidifier sensibly

A dehumidifier can be a useful tool in a London flat, particularly in bedrooms, bathrooms and rooms where laundry dries. Compressor models tend to work better in warmer rooms; desiccant models can be more effective in cold spaces. A simple humidity meter can help you see whether the room is sitting in a reasonable range — many homes aim for roughly 40 to 60 per cent relative humidity. Going much lower is not necessarily better and can feel uncomfortable.

Run the dehumidifier with doors and windows closed in the room you are treating, and clean the filter as instructed. It is a support tool, not a substitute for ventilation.

Clean small mould patches, flag the bigger stuff

If you spot small patches of mould on silicone, grout or paint, clean them promptly with an appropriate product and dry the area. Wear gloves and ventilate the room. Avoid dry-brushing mould, which can send spores into the air. If the mould keeps returning in the same place, stop treating it as a cleaning problem and start asking why the area is staying wet.

Contact your landlord or managing agent if you see persistent damp patches, water staining, a leaking roof or pipe, failed extractor fans, broken windows or mould that returns quickly after cleaning. Keep photos and dates. Landlords are responsible for certain repairs and for the structure of the property, while tenants are usually expected to ventilate and clean day to day. Clear communication early is better than a bigger problem in January.

A short winter plan for every room

In the bathroom, wipe surfaces, run the fan and open a window briefly after showers. In the kitchen, use the extractor and wipe condensation from windows. In the bedroom, keep a gap between the bed and external walls and air the room in the morning. In the living room, avoid drying laundry next to cold walls and check behind the sofa. In hallways, watch for cold corners and blocked vents.

Condensation rarely disappears by itself in winter. But with a daily wipe, regular air changes, a working extractor and a bit of space behind the furniture, a London flat can stay noticeably drier — and that makes mould far less likely to settle in.