How to Spot and Treat Penetrating Damp

Penetrating damp is when moisture gets into your house through the roof, walls, windows or doors – basically anywhere that isn’t through the floor. It’s often known as rain penetration.

Penetrating damp can be a health hazard and cause structural damage, so it’s important to treat it as quickly as possible. Keep reading to find out how to spot penetrating damp and what to do about it.

How do I know if my property has penetrating damp?

There are a few common signs of penetrating damp that you could find in your property. Look out for:

  • Mould
  • Small patches that are permanently damp
  • Damage plaster
  • Tidemarks or discoloured areas
  • Peeling paint or wallpaper
  • Rotting floor or skirting boards

What should I do if I think there’s penetrating damp in my home?

There are two main reasons why your home could have penetrating damp. Either the external ground is above your internal floor level or there are building defects that are letting moisture in.

If you want to solve a damp problem, start by looking for building defects around the damp areas in your home. This could be things like faulty roofing, cracked brickwork, leaking pipes or poorly fitting door or window frames. Fixing any of these could be a quick way to clear up the damp problems in your home.

If you can’t find any building defects or fixing them doesn’t solve the problem, you may need a more specialised damp treatment. This could involve fitting a membrane or a cavity tray if you have cavity walls. You might also need to lower the ground level outside your property.

The best way to work out how to solve a penetrating damp problem is to speak to a professional. They’ll be able to inspect your home and tell you what the best treatment is. You can then either do it yourself if you’ve got the skills or hire them to do it for you.

If you need to get in touch with a damp proofing professional to get advice or a penetrating damp treatment, click ‘Start my project’ and fill in our online form. We’ll put you in touch with up to 4 damp proofing professionals in your area.


Approx. £70 - £100 per square metre

To fit a damp proof membrane


Approx. £200 - £1,300

To lower external ground level


From approx. £3,500

To repoint an average semi-detached house

Working time

Approx. 1-3 days

Depending on the treatment and area

Advantages and disadvantages
  • Prevents penetrating damp from spreading
  • Prevents damp from damaging your property
  • Makes your home a healthier place to be