Main causes of damp walls

28 February 2025

Living in a home with damp walls is not only uncomfortable but can also damage the building and impact your health.

It’s better to find the cause of dampness early on so that you can address the problem quickly and with less expense.

We explain the leading causes of damp walls and what you can do to treat them.

EASY AS HACK

Diagnosing the main causes of damp in walls is essential, as is understanding that dampness and mould may be due to several issues.

AT A GLANCE

The signs of damp walls include:
Wet patches	Mould
Damaged paint	Stains
Peeling wallpaper	Moist, musty smell
Crumbling plaster	Rotting skirting boards

DIFFERENT TYPES OF DAMP

Knowing the type of damp you’re facing will help you solve dampness and mould problems in the long term. Covering the surface with paint, plaster or plasterboard is tempting, but it will mask the problem rather than address it.^[9]

Rising damp

Rising damp is often found in older properties, which you can identify by salt deposits reaching 90cm or more and tidal marks or stains on the walls and floors. ^[1] It can be caused by the movement of groundwater up through building materials like bricks or concrete.^[2]

Penetrating damp

Penetrating damp happens when water gets into the exterior walls or roof and the moisture builds up because of defects, so you see dampness coming through walls. If you spot green staining on the outside walls, it may show that rain is getting in.^[1] ^[4]

Condensation

The third cause of damp walls is condensation, which forms when the warm air inside your home cools and condenses on cold walls.^[3]

Condensation is the most common type of damp and is more apparent from October to April, depending on the outside temperature.^[2]

Read related article: How to tackle damp,mould and condensation
Read related article: How to prepare your property for Autumn

WHAT CAUSES DAMP WALLS?

The cause of damp walls is the development of excess moisture in the air inside buildings, and there’s nowhere for it to escape.^[5]

Rising damp

Rising damp is often found in older properties, which you can identify by salt deposits reaching 90cm or more and tidal marks or stains on the walls and floors.^[1] It can be caused by the movement of groundwater up through building materials like bricks or concrete.^[2]

Insufficient damp proofing

Failure or absence of a damp-proof course (DPC), typically found 15cm above ground level, is a major cause of rising damp. DPCs are present in most buildings constructed after 1875.^[2]

Plumbing issues

Defective plumbing can cause leaks that affect walls and ceilings, causing damp patches that may get bigger if no one fixes the leak – even if it’s tiny.

Leaking gutters

The reasons behind penetrating damp include missing or broken roof tiles, blocked gutters and downpipes, and damage to the render or cladding.^[3]

Cold spots

Condensation is common in poorly heated and insulated homes. However, our energy-efficient homes have improved insulation, such as double or triple glazing, that helps to trap the moisture in the air.^[2]

If your home has cold spots on a wall, it could indicate poor insulation where the heat can escape. You need to find the cause behind them.

Start by checking for leaks around windows and doors, as these may allow more cold air in and let warm air out (read how to draught-proof your home using DIY techniques).

Another factor could be a structural defect, such as leaky pipes.

SYMPTOMS OF DAMP WALLS

The main ways you can identify dampness on walls are:

A musty smell
A damp feel
Salt ‘tide marks’ on the wall
Brown stains on walls and ceilings
Peeling wallpaper
Damaged paint and plaster
Rotting skirting boards
Black mould

A specialist in dampness will gauge the amount of moisture in the surface using a damp meter.

HOW TO STOP WALLS GETTING DAMP

If moisture is not released, daily activities such as breathing, cooking, drying clothes, and showering can cause moisture buildup on internal walls. To prevent damp walls and create a healthy home, ensure sufficient ventilation and balance moisture.

The moisture we generate depends on how we use our homes and the number of people in them. A family of four will generate 280 full buckets of moisture per year compared to 100 buckets by a working couple.^[5]

Ensure rooms have ventilation

To ensure your rooms have ventilation, open windows and trickle vents and turn on extractor fans, air supply or extract valves, and cooker hoods when cooking. Even opening your windows daily for a few minutes could prevent moisture build-up. ^[5]

When using the central heating, set it to a modest background heat in all the rooms, even if unused.^[1]

Check pipes and gutters

Regular maintenance will help to prevent water from entering through the walls. Pay attention to the pointing, roof coverings, flashings, gutters and downpipes. Inspecting your home’s brickwork, stone and mortar for deterioration by the sun, rain and cold is also a good idea. ^[1]

Dry clothes outside or use a dehumidifier

Aim to reduce how much moisture you generate. One way to do this is to dry your clothes outside if possible. If you don’t have a garden or it’s raining, use a dehumidifier to remove the moisture. ^[5]

Treatments

The different treatments to prevent dampness will depend on whether it’s rising, penetrating, or condensation.

Reduce the humidity in your home by opening windows and trickle vents and using extractor fans and dehumidifiers.^[1]
Fix any water source coming into the house, such as leaking pipes and roofs, blocked gutters and downpipes. ^[4]
Wear gloves, a mask, and goggles, and remove mould promptly using an appropriate mould and mildew product (not bleach). ^[4]
Eliminate anything bridging the damp proof course.^[1]

If the cause is a fault with the building, such as faulty masonry or brickwork, you may need professional help from a specialist CSRT-qualified surveyor to identify it. The solutions they suggest might include: ^[1]

A ventilation system that replaces indoor air with filtered air, air low in moisture or external air. ^[1]
A retrofitted physical or chemical damp-proof course to correct rising damp ^[1], although these may damage a building built before 1919. ^[2]
Tanking walls to provide a waterproof barrier (depending on the wall and the building structure).^[1]

FAQs

Can you claim on insurance for damp walls?

Insurers usually only cover sudden damage, not damage that happens over time. They also do not cover damage due to lack of repair or maintenance.

However, damp may possibly be down to an insurable event which could be covered, such as an escape of water from a hidden pipe.

Can professionals treat damp walls?

Yes, an experienced professional can treat damp walls in your home

Can damp go on its own?

Damp will not go away on its own. You must treat it.

What can happen if damp is left untreated?

Leaving damp untreated can cause severe damage to a wall. Lack of proper ventilation can cause condensation, which leads to damp walls and damaged plaster and timber, increasing the possibility of dry or wet rot on wooden floors.^[2]

Can damp walls make you ill?

Dampness and mould (a form of fungus) are associated with many health issues, including asthma, rhinitis, coughs, and sinusitis, and have a severe effect on people with respiratory problems and weakened immune systems.[8] According to BRE, the NHS spends £1.4 billion a year treating illnesses associated with damp or cold housing.