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Damp: What is it and how serious can it be?

Updated: Dec 1, 2023

The word "damp" can strike fear into house buyers and homeowners. But damp comes in many forms. Yes they are all caused by high levels of moisture where it shouldn't be and if left untreated will become problematic with damage to walls or the growth of mould, but some are more serious than others.

So what are the different kinds of damp? What causes them and how serious are they? This quick guide gives you the basics you need to know!

Rising Damp

This is potentially the most serious and costly to repair. Rising damp is caused when moisture from the earth soaks up through your walls and foundations like a sponge.

This can cause damp patches to form around the lower parts of your walls, under flooring etc. But more seriously as the damp is penetrating your walls and foundations, it can over time cause structural damage if left untreated.

Nowadays most properties protect against rising damp with a "Damp Proof Course". This is a protective, waterproof barrier laid below the concrete slab of your foundation and between some of the blockwork which needs to be at least 150mm above ground level.

Diagram of a common method of installing a Damp Proof Course

Occasionally, depending on how the blockwork is complete, you can see evidence of a damp proof course on the outside walls of a property.

Damp Proof Course Visible in Blockwork

When this waterproof layer either breaks down, becomes damaged or was installed badly, rising damp can occur.

In these cases, it can be remedied through several methods which range in price and effectiveness. This should be discussed with a builder or engineer with experience of damp proofing.

Penetrating Damp

Penetrating damp or "Water Ingress" is when water gets in through the external walls and into the property. This can be caused by a defect in the blocks or when blocks degrade over time and become porous.

This can cause damp patches to form on the inside of internal walls and can lead to flaking plaster, paint, bubbly wallpaper or more serious issue like wet rot or mould.

A sever case of penetrating damp

There are several kinds of treatment for penetrating damp depending on the cause. The cost also depends on how much damage has been done which will need to be repaired.


Condensation is one of the more common and thankfully less serious kinds of damp. But, should still be treated once found!

Condensation happens when moist air come in contact with cooler surfaces like an external walls or around windows. This is just like how condensation will form on the outside of a cold drink on a warm day!

When this condensation gets on the walls, it can seep into the wall causing damage to the surface of the wall and/or mould to form.

Damp caused by condensation

Quite often, it forms in rooms with poor ventilation, or somewhere air is prevented from circulation - like behind a couch.

Most of the time, this can be treated by thoroughly cleaning the area, applying a layer of damp proof paint, and opening a vent in a room.

However, if left untreated, like other kinds of damp it can cause more serious problems.

Damp from leaks!

Probably the most obvious way water gets where it shouldn't is through leaks!

The ceilings in rooms below bathrooms are prime locations to spot this kind of damp. It could start as a very light yellow patch on the ceiling and can be caused by even the smallest of leaks.

Signs of a leak from upstairs!

Thankfully, once you spot a leak a trusty plumber will be able to sort it for you! But depending on how long the leak has been happening, the repair may range from a new coat of paint to new plasterboards and plastering!

Will a pre-purchase survey check for damp?

Yes! From the moment the surveyor is walking towards the property they will be looking for evidence of a damp proof course. Then when in the property they will visually check every room for signs of damp and then use a moisture meter on the walls, ceilings and floors of common problem areas to ensure the moisture levels are within acceptable levels.

If any signs of damp are found, the surveyor will include them in the written report along with pictures (if the damp is visible). If the cause is known, they will also mention this and suggest a recommended course of action.

At all of our surveys are experts in spotting signs of damp. To book your survey with us, just go to and click on "Get Survey Now".

Further Reading


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