Damp in the home: causes, symptoms and treatments

In this article

Signs of damp
Causes of damp
Penetrating damp
Leaking pipes
Condensation
High humidity
How to prevent damp
Dehumidifiers
Installing a damp-proof course
Cleaning mould
Decorating a damp house

What are the signs of damp?

Damp problems in houses in the UK are usually most obvious – and most prevalent - during the winter. If your ceilings are discoloured, your walls cold, slightly clammy or covered in black, speckled marks, or your wallpaper is curling and/or paint flaking, your home needs your attention.

Another sign that there are high levels of moisture in your house or flat is condensation on the windows in the morning, or black mould on frames and around the edge of baths and sinks, where silicone sealant has been used.

Moisture can be a symptom of damp but it can also cause damp, so it needs sorting out. Black mould on fabric also indicates a problem, as does a musty smell, which you'll often find in cupboards or basements that are damp.

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Brown stains are often a sign of penetrating damp, which can be caused by leaking gutters, broken roof tiles, blocked drains or cracked render. Outside ground level higher than the internal floor can also cause penetrating damp, making basements particularly susceptible.

What causes damp?

Penetrating damp

Symptom: brown stains on ceilings or walls
Likely cause: a brown stain on a ceiling, on the inside of an exterior wall or on a chimney breast is most likely to be penetrating damp, which is caused by broken or loose tiles or slates, blocked or leaky gutters, damaged flashing and chimneybreasts and dodgy rendering or mortar on outer walls.

Leaking pipes

Symptom: expanding damp patch on ceilings and floors
Likely cause: if your plumbing is leaking, you'll find an expanding damp patch somewhere on a ceiling or underneath a basin, sink, bath or radiator. Sometimes a long-term, slow trickle from something like a radiator can go unnoticed for years, rotting joists without you ever realising you have a problem until your floor goes spongy.

Condensation

Symptom: condensation on windows, wet walls, peeling paper
Likely cause: condensation occurs when warm, moist air touches a chilly windowpane or a cold external wall, and causes wet windows, and over time, black marks and mould.

High humidity

Symptom: humidity of over 60%, mould and mildew, musty smells
Likely cause: moisture generally is a common cause of damp in the home. It's generated through normal household activities like cooking, washing, showering, and drying wet laundry without proper ventilation. Other causes of damp - leaking pipes, condensation and penetrating damp, can all increase humidity too.

Chartered surveyor John Conlin answers reader questions on damp

How to prevent damp

These are the steps you can take to reduce the amount of damp in your house.

Allow air to circulate

Whether your property is old or new, if you have renewed your insulation you will probably have some kind of mould somewhere if air isn't circulating efficiently. To keep moisture at bay, open your windows every day and let fresh air circulate around the house.

Place furniture a few inches away from external walls, to allow air to circulate.

Keep curtains and blinds clear of windows if they're prone to condensation.

Keep temperature steady

Insulating an attic can help create a warmer home, and secondary or double glazing will help to avoid condensation on windows because the inner pane of glass is insulated against the cold air outdoors.

Heat all the rooms in a home to equal temperature, as it's often the difference in temperature between two rooms that causes window condensation.

Prevent moisture build-up

Close the bathroom door and open the window when showering, or install an extractor fan in bathrooms, so moisture is instantly whipped away.

When it's not raining, open a window in each room for 15 minutes a day.

Cover pans with a lid when cooking to cut condensation on kitchen windows. Switch on the cooker hood fan when using the hob, and leave on for a few minutes when finished, to clear the air. Replace filters regularly or if suitable, wash in the dishwasher.

Dry laundry outdoors when you can, or use an efficient tumble dryer. A condenser dryer doesn't need a vent to the outside and won’t allow moist air to escape into your home.

Dehumidifiers extract moisture from the air and store it in an internal bucket. Empty the bucket regularly as it can fill quickly in a very humid room. Dehumidifiers often have a laundry mode to help when drying clothes indoors.

Control humidity

Buy an electric dehumidifier to reduce humidity levels and make your home less hospitable to condensation, mould, mildew and other allergens like dust mites.

A 'smart' model will switch on automatically when humidity rises about a certain percentage. Water will collect in a bucket and need emptying at regular intervals - the damper the house the more often you will need to empty your dehumidifier. The normal range of dampness in a UK house is between 40- 60% and can be measured with a  hygrometer, available for around £10. When the humidity level reaches over 60% you are more likely to experience mould growth, especially if the room is 20C or warmer.

Pop a moisture absorber in a damp, musty cupboard to keep it dry.

Find out about some of the best dehumidifiers to buy

See to your chimney

The causes of chimneybreast damp include rubble down the chimney or chimneys that have been blocked up – at the top or the bottom - so the bricks can't breathe. Open up any vents in your fireplace to give the flue a good airing, and get the chimney checked by an expert.

Keep on top of maintenance jobs

Keep on top of maintenance on the outside. Check your roof in spring and autumn and after storms. Clear gutters at the same time, and install gutter guards to stop leaves clogging them up, and keep an eye on crumbling mortar or cracked walls.

If your problem is the roof, a specialist roofer will repair broken or loose slates or damaged flashing. They will also clear gutters - but you might need a builder to repair mortar and render on the outside walls.

An expanding wet patch on the ceiling can mean there is a leak upstairs. Check radiators, pipes, sinks and show cubicles for leaks. Plumbing leaks can also cause floorboards to become soft over time.

Locate plumbing leaks

If you suspect your plumbing is leaking, call in a plumber. It can be a long job locating a leak from a radiator and if the joists and/or flooring is affected you will need to employ a joiner or builder to do the repairs.

Install a damp-proof course

Rising damp is usually found in older homes, where damp-proof courses aren't automatically built into the construction, and new windows (double-glazed for example) and non-porous paint and other renovations have made it hard for moisture to escape. In older buildings, brick walls may absorb moisture from the ground, so installing an up-to-date damp-proof course is the answer. There are a number of methods, so consult an expert to find the best one for your style of home - and ensure you get a long-lasting guarantee on the work.

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Cleaning mould

Mouldy silicone around the bath or shower can be replaced by using sealant remover, a product that dissolves it. Then replace the silicone with a mould-resistant variety.

If walls are mouldy, wipe down with mild detergent, then dry with a clean rag. Be aware that mould spores can cause allergies, so if you're tackling a big patch, keep windows open and wear a protective mask and rubber gloves.

Mould grows on organic surfaces such as wood, wool carpets, paper, fabric and plasterboard. It is unlikely to grow on metal, plastic or glass unless there is dust or grease on it, so keep surfaces clean to reduce the risk of mould coming back.

Decorating a damp house

If you have a wall re-plastered or brickwork replaced, let the wall dry out thoroughly before applying paint. This means keeping it at an even temperature and ensuring the room is ventilated.

Do your painting and decorating when the weather is fine and you can leave windows and doors open to ventilate the space.

Choose wall finishes that resist moisture – Dulux make a huge range designed specifically for kitchens and bathrooms. They wipe clean, keep mould at bay and repel condensation.

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