The heating goes on, the windows stay shut, and within a few weeks the black spots appear: in the corner of the bedroom ceiling, behind the wardrobe, around the bathroom window. Damp and mould is the most common home repair question in the UK every autumn and winter, and older Scottish tenements and pre-war houses are especially prone to it.
The good news is that most cases are caused by condensation and can be fixed for a few hundred pounds. The bad news is that damp is also one of the easiest problems to misdiagnose, and expensive "rising damp" treatments are sometimes sold for problems they will not fix.
This guide explains how to tell the three types of damp apart, what each fix really costs in 2026, and what has changed for renters since Awaab's Law came into force in Scotland on 6 October 2026.
The quick answer
- Mould in corners, on ceilings, behind furniture or around windows is almost always condensation. Fix it with ventilation, steady heating and better extraction, often for under £500.
- A damp patch that grows after rain, often on an outside wall or chimney breast, is usually penetrating damp. Find and fix the leak first (gutters, pointing, roof, window seals).
- A tide mark up to about 1 metre high on a ground-floor wall, with crumbly plaster and white salts, may be rising damp. It is much rarer than many quotes suggest, so get an independent diagnosis before paying for a damp proof course.
- Renting? In Scotland, all landlords must now investigate damp and mould within 10 working days and start any repairs within 5 working days after that.
The three types of damp
| Type | Where you see it | Typical signs | Usual cause |
|---|---|---|---|
| Condensation | Corners, ceilings, window reveals, behind furniture, bathrooms, kitchens | Black spotty mould, water droplets on glass, musty smell, worse in winter | Moist indoor air meeting cold surfaces |
| Penetrating damp | Outside walls, chimney breasts, ceilings under roofs | Damp patch that spreads or darkens after rain | Blocked or broken gutters, failed pointing, roof or flashing defects, leaking window seals |
| Rising damp | Bottom of ground-floor walls only | Tide mark up to about 1 m, salts on the plaster, peeling paint and skirting rot | Missing, failed or bridged damp proof course |
Many homes have more than one type at once. A small leak can make a cold wall colder, which then attracts condensation and mould.
Is it condensation? A five-minute check
- Look at the pattern. Condensation mould is usually spotty, in cold corners and behind furniture, and higher up the wall. Rising damp stays low.
- Check the windows in the morning. Heavy water on the glass and frames means the air in your home is too humid.
- Think about your routine. Drying clothes indoors, cooking without lids, long showers with the fan off and keeping trickle vents closed all add a lot of moisture.
- Try a cheap hygrometer. If indoor humidity regularly sits above about 60 to 65%, condensation is very likely.
- Watch the weather. If the patch gets worse after rain rather than after cold, dry spells, suspect penetrating damp.
What it costs to fix damp and mould in 2026
These are typical UK price ranges published by trade cost guides in 2026. Prices vary by region, property size and access, and are usually higher in London and the South East.
| Job | Typical cost |
|---|---|
| Professional mould inspection | £150 to £300 |
| Independent damp survey | £100 to £600 |
| Mould treatment, single wall | £150 to £200 |
| Mould treatment, whole property | £725 to £1,100 |
| Replace an extractor fan like-for-like | £80 to £150 |
| New extractor fan ducted through an outside wall | £250 to £450 |
| Positive input ventilation (PIV) unit, unit only | about £300 to £1,000, plus an electrician to connect it |
| Injected damp proof course, terraced house | £800 to £1,200 |
| Injected damp proof course, semi-detached | £1,500 to £2,500 |
| Injected damp proof course, detached | £2,000 to £5,000 |
| Tanking a cellar or basement | about £125 per m² |
Remember that damp proofing quotes often leave out replastering, redecorating and time for the walls to dry, which can add a lot to the final bill. Always ask what is included.
Fixes you can do yourself this week
- Keep the heating steady. A low, constant temperature keeps walls warmer than short blasts of heat followed by cold.
- Ventilate at the source. Use extractor fans while cooking and showering and leave them running for 15 to 20 minutes afterwards. Open trickle vents and keep the bathroom door closed while it clears.
- Dry clothes outside or in a vented dryer where you can. If you must dry indoors, do it in one room with the door closed and a window slightly open or a dehumidifier running.
- Move furniture a few centimetres away from outside walls so air can circulate behind it.
- Clean small patches of mould safely. Wear gloves and a mask, use a mould-removal spray made for the job, and wipe with a disposable cloth. Do not brush dry mould, which spreads spores.
- Check gutters and downpipes after heavy rain. An overflowing gutter is one of the most common causes of a damp patch on an upstairs wall.
Tip: Cleaning mould without fixing the cause only buys you a few weeks. If it keeps coming back in the same place, the room needs better ventilation, more consistent heating or a repair outside.
When to call a professional
Get help from a qualified tradesperson if:
- the mould covers a large area (as a rough guide, more than about a square metre) or keeps returning after cleaning
- plaster is crumbling, wallpaper is lifting or skirting boards feel soft
- there is a damp patch that gets worse after rain
- your bathroom or kitchen has no working extractor fan
- someone in the home has asthma, a respiratory condition or a weakened immune system, or there is a young baby
For condensation, the right person is often an electrician (fans and PIV units) or a general builder. For penetrating damp, it is usually a roofer or a builder who does pointing and gutter work. Save the damp proofing specialist for problems that are genuinely at the base of the wall.
Watch out for the rising damp upsell
Rising damp does exist, but it is far less common than condensation and penetrating damp. Before you pay for an injected damp proof course:
- Ask how the diagnosis was made. Handheld electronic moisture meters are designed for timber and can give high readings on plaster that contains salts, even when the wall is not wet. Better surveys use methods such as calcium carbide testing or take samples.
- Ask what else was ruled out. Has the surveyor checked that outside ground levels, paths or rendering are not bridging the existing damp proof course? Sometimes lowering a flower bed or clearing an air brick solves the problem.
- Consider an independent survey from a surveyor who is not selling the treatment.
- Get at least three itemised quotes and check what guarantee is offered and who stands behind it.
Renting? Your rights under Awaab's Law
Awaab's Law is named after Awaab Ishak, a two-year-old who died in 2020 after long exposure to mould in his family's housing association flat in Rochdale. It sets legal deadlines for landlords to deal with damp and mould.
Scotland (in force since 6 October 2026)
Awaab's Law now applies to most social and private tenancies in Scotland. When a tenant reports damp or mould, the landlord must:
- Investigate within 10 working days, using a competent person.
- Give the tenant a written summary within 3 working days of finishing the investigation.
- Start any repairs needed within 5 working days of finishing the investigation.
If a landlord cannot meet these timescales, they must explain why in writing. Private rented homes must also meet the Repairing Standard, which requires a home to be substantially free from rising or penetrating damp. If a private landlord does not act, tenants can apply to the First-tier Tribunal for Scotland (Housing and Property Chamber).
England
In England, Awaab's Law has applied to social housing (council and housing association homes) since October 2025. Landlords must fix emergency hazards within 24 hours. For significant damp and mould hazards, they must start investigating within 10 working days, give a written summary within 3 working days of the investigation, make the home safe within 5 working days, and begin any further work within 12 weeks at the latest. From 30 November 2026, the law extends to more hazards, including excess cold and electrical hazards.
The government has said Awaab's Law will be extended to private renting in England. Check the latest guidance on GOV.UK, as the rules for private tenants were still being phased in at the time of writing.
Tip: Always report damp and mould to your landlord in writing (email is fine), with dated photos. The deadlines start from when the landlord is told or becomes aware of the problem.
This section is general information, not legal advice. Shelter Scotland, Shelter (England) and Citizens Advice can help with your specific situation.
How to hire the right person for the job
- Describe the problem clearly: where the mould is, how long it has been there, whether it changes with rain or cold, and photos.
- Ask for a diagnosis before a price. A good tradesperson will explain the cause, not just sell a product.
- Compare at least three written, itemised quotes.
- Check what is excluded, especially replastering, redecorating and making good.
- Ask about guarantees and insurance, and get them in writing.
You can post your damp or mould job on GetMaster for free and compare quotes from approved local tradespeople. There is no obligation to hire.
Frequently asked questions
Is black mould dangerous to health?
Mould can cause or worsen breathing problems, allergies and asthma. Babies, older people and anyone with a respiratory condition or weakened immune system are more at risk. Deal with it quickly and speak to your GP if you are worried about symptoms.
Should I use bleach on mould?
Bleach can remove the colour from mould on hard, shiny surfaces, but it often does not deal with mould in porous materials such as plaster and silicone. A purpose-made mould-removal product is usually more effective. Never mix cleaning products, and always fix the cause of the moisture.
Will a dehumidifier stop condensation mould?
A dehumidifier helps a lot, especially in a room where you dry clothes, but it works best alongside good ventilation and steady heating. It will not fix penetrating or rising damp.
Does home insurance cover damp and mould?
Usually not. Most policies exclude gradual damage such as condensation and long-term damp. Sudden events, such as a burst pipe, may be covered, so check your policy wording.
How long does a damp proof course take?
The work itself typically takes one to four days, but the walls can take several months to dry out fully before final decoration. Your installer should tell you how long to wait before replastering and painting.
My landlord says the mould is my fault. What can I do?
Lifestyle can contribute to condensation, but landlords still have to investigate properly and fix problems with the building, such as missing extraction, leaks or poor insulation. Keep a written record and photos, and contact Shelter, Shelter Scotland or Citizens Advice for advice.
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Get free quotesThis article is general information, not professional advice. Costs are indicative and vary by region, property and specification. Last updated 20 October 2026.