Is it condensation, damp or mould?

Black spots in the bedroom corner, streaming windows every morning, a brown patch on the ceiling after a wet week: by late autumn most homes show at least one of these. They are often all called "damp", but they have different causes and very different fixes. Getting it wrong costs money, because the cure for condensation is a few habits and an extractor fan, while the cure for a leaking gutter is a ladder, and the cure for real rising damp is building work.

This guide explains how to tell condensation, penetrating damp and rising damp apart, where mould fits in, what you can fix yourself, and who to call when you cannot.

How common is damp in UK homes?

More common than it was. The government's English Housing Survey, published in January 2026, found that 1.4 million homes in England (5 percent) had a problem with damp in 2024, an increase on 2022. Damp was most common in private rented homes (10 percent), then social rented homes (7 percent) and owner occupied homes (4 percent).

The same survey shows which kind is most likely. Severe condensation was the most common form, in 3 percent of homes, followed by penetrating damp at 2 percent and rising damp at 1 percent. So if you are not sure what you have, condensation is the best first guess, and rising damp is the least likely.

The three types of damp, and where mould fits in

Government guidance, Understanding and addressing the health risks of damp and mould in the home, describes the main types like this, and calls condensation the most common.

Condensation

Everyday life puts a lot of water into the air: cooking, showers, kettles, breathing and, above all, drying washing indoors. When that warm, moist air meets a cold surface it turns back into water. You will see it on windows, in the corners of outside walls, on bathroom ceilings, and behind wardrobes and beds pushed against cold walls. It is worst on cold mornings and in rooms that are not heated much.

Penetrating damp

Water getting in from outside through a defect in the walls, roof, windows or floors. It shows as a patch, often with a darker edge, that grows after heavy or wind driven rain and shrinks in dry spells. It can be at any height. Common causes are blocked or cracked gutters and downpipes, slipped or missing roof tiles, worn pointing or cracked render, and failed seals around window frames.

Rising damp

Moisture drawn up from the ground into the bottom of a wall, usually in older homes where the damp proof course has failed or been bridged. Tell tale signs, as listed by Hartlepool Borough Council's housing team, are a tide mark on ground floor walls, damp up to about a metre high and white salt deposits on the plaster. It does not come and go with the weather much.

Leaks

The guidance also lists damp from leaking pipes, overflowing baths or sinks and burst pipes. A patch under a bathroom, or one that appears suddenly, is often a plumbing leak rather than damp at all. If a pipe has burst, our guide on how to stop pipes freezing and what to do if one bursts covers what to do first.

Mould

Mould is not a fourth type of damp. It is what grows when any of the above keeps a surface wet. Black, spotty mould on window reveals, ceilings and the backs of cupboards usually means condensation. Mould on a patch that also has a tide mark or a stain spreading from outside points to water coming through the wall.

How to tell which one you have

Four questions settle most cases:

1. Where is it? Windows, cold corners and behind furniture suggest condensation. A patch on an outside wall or ceiling suggests penetrating damp. A band along the bottom of a ground floor wall suggests rising damp.
2. When does it get worse? After showers, cooking and drying clothes: condensation. After rain: penetrating damp. Roughly the same all year: rising damp.
3. What is outside? Stand back and look at the wall from outside, directly behind the damp patch. Overflowing gutters, a dripping downpipe joint, a missing tile or a crack in the render are strong clues. So is soil, a flower bed or new paving piled up higher than the damp course, which is the line of slate or plastic usually about two bricks above the ground.
4. What does the foil test show? Tape a square of kitchen foil tightly to the damp wall and leave it for a day or two. If droplets form on the room side, the moisture is coming from the air, which means condensation. If the wall under the foil is wet, the water is coming through the wall.

It is common to have more than one at once. A cold wall made damp by a leaking gutter will also attract condensation, so fix the outside problem first and then see what is left.

How to reduce condensation yourself

Condensation is the one type you can usually solve without a tradesperson. The government guidance and council advice agree on the basics:

• Keep rooms steadily warm. Hartlepool Borough Council suggests 18 to 21 degrees in cold weather. Low, steady heat keeps walls warmer than short bursts.
• Get the moisture out where it is made. Use extractor fans when cooking and showering and leave them running for a while afterwards, put lids on pans, and close kitchen and bathroom doors so the steam does not spread.
• Dry washing outside if you can. If you cannot, use a room with the door shut and a window open, or a dehumidifier. Avoid drying clothes on radiators.
• Let air move. Keep window trickle vents open, do not block air bricks or vents, and leave a small gap between furniture and outside walls.
• Wipe windows and sills on cold mornings so the water does not soak into frames and plaster.
• Insulate. The government guidance notes that homes which are poorly insulated or hard to heat are more prone to condensation, and that bringing loft insulation up to at least 270mm is particularly effective.

To clean mould, use a fungicidal mould wash, ideally one with a Health and Safety Executive approval number, and follow the label. Do not brush it dry, which spreads spores, and do not paint over it without treating it first.

Why damp and mould matter for health

This is not only about decorating. The government guidance says damp and mould mainly affect the airways and lungs, causing coughs, wheezing, breathlessness and infections, and making asthma and other lung conditions worse, and in the most severe cases it can cause death. It lists children, older people, pregnant women and anyone with a lung condition, a weak immune system or limited mobility as most at risk. If someone in your home is in one of those groups, deal with damp sooner rather than later.

When to call a tradesperson, and which one

• Penetrating damp: fix the cause outside first. That may be a gutter clean or repair, a roofer for slipped tiles or flashing, or a builder for pointing, render or window seals. Treating the inside wall before the outside is fixed is money wasted.
• Suspected rising damp: book an independent damp survey before agreeing to any treatment. Many things look like rising damp, including bridged damp courses, high ground outside, leaking pipes and condensation itself. Ask whether the surveyor is a member of the Property Care Association, the trade body for damp and timber specialists, and ask for a written report showing how they reached their diagnosis.
• Condensation that will not go away: a damp specialist or electrician can fit humidity controlled extractor fans or a positive input ventilation unit, and a plumber or heating engineer can check radiators that are not heating a cold room properly.

Whoever you use, get the diagnosis and the price in writing before work starts. Our guide on how to check a tradesperson is genuine covers the checks worth doing.

If you rent: who is responsible?

In England, landlords of most homes let for under seven years must keep the structure and exterior in repair under section 11 of the Landlord and Tenant Act 1985, which covers leaking roofs, gutters and walls. The Homes (Fitness for Human Habitation) Act 2018 also requires the home to be fit to live in, and serious damp can make it unfit. Tenants are expected to heat and ventilate reasonably.

Social landlords now have legal deadlines too. Under Awaab's Law, in force since 27 October 2025, a council or housing association must investigate significant damp and mould within 10 working days of becoming aware of it, give you a written summary within 3 working days of the investigation, and start safety work within 5 working days where there is a significant risk. Emergency hazards must be investigated and made safe within 24 hours.

Whoever your landlord is, report damp in writing with dated photos, and keep copies. If a social landlord does not respond properly, you can complain to the Housing Ombudsman; private tenants can contact their local council's private housing team.

Find a local damp specialist

If you own your home and the damp is not simple condensation, post your job free and hear back from a local damp and mould specialist. Describe where the damp is and when it gets worse, add a photo of the inside and the outside wall, and the business you choose can come back to you with a price. You pay them directly, and there is nothing to pay online.

Or browse local businesses: damp specialists in Birmingham, damp specialists in Wolverhampton, damp specialists in Coventry, damp specialists in Walsall, damp specialists in Dudley or damp specialists in Solihull. For more winter guides, see all our home advice.