How to spot signs of damp

Damp can be a horrible problem to live with. In addition to making your home feel cold and uncomfortable, it can wreck your decor, damage your furniture and exacerbate health problems like asthma.

In severe cases it could cause structural damage to your home.

Find out how to spot it and fix damp with our guide, and whether it's covered by your home insurance

A wall that's damp


What is damp?

Damp is the existence of condensation or other moisture on the structure of a property.

The build-up of moisture can lead to a host of problems, and if you don’t deal with it the result can be serious damage to the building’s infrastructure.

Damp problems tend to increase over time, but if you don’t know where to look they can happen invisibly. And by the time they’re spotted, major work can be required to put things right.


What causes damp?

If a house is suffering from a damp problem, it means there's unwanted moisture. It's usually found in the walls, ceilings or floors.

A damp problem can occur when water or moisture works its way into your house. This can simply be as a result of condensation around windows, but there can be plenty of other causes.

These include:

  • Leaking or burst pipes and overflows – you could consider getting trace and access cover to protect yourself against the cost of finding the leak
  • Broken or missing roof tiles that let water in
  • Blocked gutters
  • Leaking windows
  • Moisture rising up from the ground, particularly if there’s no damp-proof course or the damp-proof course is damaged
  • Bricks that are porous
  • A leaking dishwasher or washing machine
  • Seemingly innocent household tasks can also be problematic if there’s not adequate ventilation, such as drying wet clothes, showering, bathing or cooking.

A small patch of damp on a wall initially might not seem too bad, but if it's not dealt with it may cause more serious structural problems to your home. And you could find that if you want to claim for the costs on your home insurance, it doesn’t cover it.


Types of damp

There are 3 main types of damp:

  • Rising damp
  • Penetrating damp
  • Condensation-caused damp

Rising damp

This is where moisture rises up from the ground through walls in a capillary action. Newer houses should have a damp-proof course to guard against damp, but they can be compromised over time.

Signs of rising damp include:

  • Damp patches that start at the base of a wall and gradually move upwards
  • Rotting skirting boards or plaster
  • Floor coverings such as tiles, vinyl or carpets that are wet and lifting
  • Peeling paint or wallpaper
  • A white, powdery salt-like substance on a wall
  • Yellow or brown tide marks or staining on a wall

Penetrating damp

This is the result of external problems on your property, where water finds its way in from the outside. This could be anything from missing roof tiles to broken or porous brickwork as well as issues with guttering or damaged seals around windows and doors.

Signs of penetrating damp include:

  • Damp patches that move horizontally through walls, rather than up from the ground, and that might get darker when it’s raining
  • External damage, including to brickwork, and moss and algae growth
  • Peeling paint or wallpaper
  • Rotting plaster

Condensation-caused damp

This is the most common form of damp and is often the result of carrying out basic household tasks without decent ventilation.

This could include steam from cooking or drying damp clothes. The air condenses on cold surfaces and creates water.

Signs of condensation-caused damp include:

  • Damp patches and water running down walls in any room whether there’s likely to be steam, such as bathrooms and the kitchen
  • Water on windows
  • Mould around the windows

Early signs of damp

In the early stages, the only sign of a possible problem might be a musty smell.

To check for areas of damp in a house, carefully examine walls, floors and ceilings for any tell-tale signs. Feel for wet patches and peek under flooring that appears to be lifting.

If you suspect your house could have rising damp, a useful trick is to run your hands across the affected area. If it feels wet, you should be able to feel the plaster salts. These are white deposits that are washed out of the bricks and into the plaster.

If there’s wallpaper, listen for a slight crunching sound as you move your hand over the salts.

Other telltale signs that suggest damp in a house include:

  • The appearance of mould or mildew on walls, floors or ceilings
  • Water droplets on walls
  • Dark or discoloured patches on walls or plaster
  • Excessive condensation on windows, not just during the winter
  • Rotting woodwork, such as skirting boards

By far the best way to check for damp is to use an expert surveyor. The surveyor should thoroughly check for any signs of damp inside or outside the property, identify what type of damp it is and the likely cause. They should also offer advice on the best way to fix it.


How to spot damp when viewing a house

If you’re viewing a house before buying, check for signs of damp. Start in the basement if it has one.

Discolouration or damp patches on the walls is a telltale sign, and you might be able to smell it, too. The floorboards can rot if there’s damp underneath them, while walls and ceilings can show clear signs of damp.

A bathroom can be particularly susceptible to damp. Because of the constant use of hot water, mould should be easy to spot. It’s also worth keeping an eye on the airing cupboard and the water heater in there.


How to stop damp problems in the home

Problems caused by condensation can be improved by doing your best to remove as much moisture from a room as you can and improving ventilation.

To prevent condensation in the home, make sure you’re using extractor fans in bathrooms and kitchens, and keep windows open. Where you have a localised problem you might want to think about using a dehumidifier.

If you have penetrating damp due to porous bricks, replacing the bricks or painting them with silicone water-repellent paint should help fix the problem. You can get anti-damp paint from most DIY stores.

You might also be able stem the problem by fixing or replacing your gutters. But not all damp problems are easily resolved, though.

On some occasions, you might need expert help – particularly if it’s rising damp you’re up against. A surveyor should be able to accurately measure levels of damp and pin down the cause of the problem.

Some of the fixes professionals might suggest are:

  • Having a cavity tray either replaced or fitted to stop water from the outside reaching the inner wall.
  • Have a new damp-proof barrier or damp course fitted. This involves injecting chemicals into the wall to create a water-proof barrier.
  • Having the internal walls or floors sealed in damp-proofing material.

Your surveyor should advise on the best approach to resolve your damp problems and the costs involved. Costs can run to thousands of pounds so it’s always worth getting a couple of quotes before hiring a tradesperson.

To help reduce the risk of your property suffering from such a problem, keep your house well maintained and promptly deal with any problems that arise.

This is especially important as damp problems caused by poor maintenance isn't normally covered by your home insurance.


Damp diagnosis

Windows Walls Kitchens and bathrooms Basements
Feel cold and damp
Black mould on the sealant
A musty smell
Water on the sills
Mould on the windows and ceiling
Mould and stains on the walls
Black mould on window frames
Flaking paint
A musty smell
Peeling wallpaper