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22 October 2020

How to get rid of penetrating damp

We explain what could be causing your penetrating damp, from leaking gutters to blocked cavity walls, and how to deal with the problem
Old drain pipe damaged wall 442924
Liz Ransome-Croker

Fixing penetrating damp can be easy and cheap to do yourself. But, before you can treat it or decide whether to get a professional in, you'll need to identify the issue first.

1. Leaking walls

The first sign of penetrating damp is usually wet or leaking walls. Look out for a discolouration of interior walls, damp patches, mould, blistered plaster, water droplets and a wet surface, as these are all signs of penetrating damp. You'll probably need to use a specialist builder to identify and repair any long-term structural issues. Head to our Trusted Traders site to find someone near you.

2. Air gaps

Gaps in (or damage to) window frames and doors can lead to penetrating damp. Make sure your property is airtight and get damage fixed promptly if it occurs.

3. Burst gutters and pipes

You might find that your penetrating damp is being caused by water leaking from gutters and downpipes on the outside of your property, so examine them for cracks. Fixing them could well solve the problem. 

4. Porous bricks

You might also find that old bricks have become porous and are allowing water to get into your home. If this is the case, you may need to get them replaced. However, one easier option to try first is painting the bricks with an exterior silicone water-repellent fluid or limewash, that will seal your walls again while still allowing them to breathe. Damp-proof exterior paint can also be a good preventative measure, but seek professional advice first on what would work best for your home's age and building materials.  

5. Cavity wall problems

Occasionally, penetrating damp can be caused by problems with cavity walls. Walls in modern homes (and many built since 1920) are usually constructed as two layers of wall with a cavity between them, so that moisture penetrating from outside can evaporate before it gets to the inner wall.

If something 'interrupts' the wall, such as a window or pipework, you may have or need a cavity tray (see image below). These come in many different forms but effectively act as a way to drain water away from the inner wall to the outside through 'weep' holes (holes in a part of the outer wall).

If a cavity tray is defective, or there isn't one in place, you could end up with penetrating damp. In this case, you'll need to have them repaired or added.

The cavity itself can also cause damp, if it has become filled with debris, such as broken mortar or bits of brick, which take in moisture from the outer wall and pass it to the inner wall. In these cases, the debris will need to be cleared out to rectify the problem.

Find out how much these types of repairs may cost in our damp costs page

6. Poor cavity insulation

Lastly, in some rare cases, cavity wall insulation can cause damp problems. This is usually only the case if your home is exposed to severe levels of wind-driven rain or if your walls are poorly constructed or in very bad condition. You can find out more in our guide to wall insulation and damp problems.