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6 October 2020

FAQs: dealing with damp

Here we answer your frequently asked questions about different types of damp, treating penetrating damp and rising damp and damp proofing.
Man plastering wall 435874
Liz Ransome-Croker

Whether you're struggling to determine what type of damp you have or you want to know what a damp-proof course really is, we've answered the most common questions here. 

What type of damp do I have?

There are three different types of damp rising damp, penetrating damp and condensation. You can visit our individual guides for more information on each type.

If you've read our guide to types of damp but still can't work out where your damp problem is coming from, you will need some expert advice from a damp-proofing company, independent damp specialist, builder or surveyor.

You can find recommended builders, surveyors and specialist damp companies in your area by visiting Which? Trusted Traders.

Before you call out a damp-proofing company, make sure you take a look at our guide to damp costs to see the results of our undercover investigation, which found some companies recommending unnecessary work.

What is a damp-proof course?

External walls of houses generally have a waterproof barrier built into them to stop rising damp from getting into internal walls. This is often a horizontal plastic or bitumen felt strip in the wall, 15cm above the ground level. Building regulations came into force in 1875, specifying that damp-proof courses had to be built into houses, so older houses may not have one.

What is a damp-proof membrane?

A waterproof barrier that's laid under concrete floors to prevent damp.

Should I use a special kind of damp-proof paint?

You can buy anti-damp, damp-proof or mould resistant paint from most DIY stores reasonably cheaply. It claims to be particularly suitable for the areas around windows and outside facing walls.

We haven't tested it but some Which? members have told us that it's been successful for them.

Should I be worried about rot?

Rot in timber can be a major cause of structural damage to your home and occurs primarily due to damp or poor ventilation. It can be very serious – if you suspect you have rot, you should call in specialist help.

What's the difference between dry rot and wet rot?

Wet rot tends to grow on very wet timber where there is a constant source of moisture. It doesn't spread through brickwork and stops growing when the source of moisture dries up. Signs of wet rot include a black fungus and timber which feels soft and spongy and is possibly discoloured. There may also be a damp, musty smell.

Dry rot needs less moisture and can grow into non-timber materials, such as plaster and bricks. Signs of dry rot include white or orange growths, crumbling timber, deep cracks and a mushroom-type smell.

Can I get good damp advice from a free survey?

We did see some good practice in our damp-proofing investigation (go to how much does it cost to repair damp? to see the results). However, in two thirds of cases overall, the companies recommended unnecessary or inappropriate treatment, or missed the problem completely, according to our three damp experts.

If you are considering getting a ‘free survey’, get at least three companies to come to your property and quote for the work before you choose the best deal.

If there are inconsistencies in the type of work recommended, or if you are concerned that the companies may be recommending unnecessary treatment, consider getting an independent damp specialist to assess your home.

An independent damp specialist will have no vested interest in recommending unnecessary work, so should be able to give you an unbiased opinion on what kind of remedial treatment is necessary – however the report could cost between £100 and £750.

Is damp-proofing work guaranteed?

Most companies offer a guarantee – make sure you find out what's included in the price or available at an extra cost. Property Care Association members may also offer an additional insurance-backed guarantee that will cover you if the company goes bust.

How can I ensure my damp-proof course continues to work?

Generally, a damp-proof course should look after itself. However, you can avoid repeat problems by ensuring the external ground level remains 150mm (6in) below the damp-proof course, not bridging it with internal or external coats of plaster and making sure it's quickly repaired if damaged by any building alterations.

My new damp-proof course hasn't worked and a new surveyor said it was unnecessary.

Under the Consumer Rights Act, a service should be provided using ‘reasonable care and skill’. If your new damp-proof course work was unnecessary, the company that installed it has failed to use reasonable care and skill, and is therefore in breach of contract. To make a claim, you will need to prove this is the case. This is usually done by asking an independent expert agreed upon by you and the company to assess whether the work was necessary.

If the expert agrees the work was unnecessary, you can claim back money spent on the work. You may need to take the company to the small claims court to achieve this. For more information, see our guide on how to use the small claims court.