The quick guide to damp

If you have a build-up of moisture in areas of your home, follow this advice on how to tackle the symptoms and prevent long-term damage

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Whether you live in a characterful period home with original features or a contemporary property complete with energy-efficient windows and insulation, the changing seasons and unpredictable weather in the UK can cause a host of maintenance issues, including damp.

If you suspect you have damp creeping into your walls, condensation in your glazing or a leak that could cause structural problems, make sure you get on top it as soon as possible. These issues can eventually become unmanageable and expensive if they are left to get worse over time.

This quick guide will give you a general overview of the causes and treatments of damp in most homes. If you live in a period property that might have a slightly more complex damp problem, read our complete guide to dealing with damp in old homes.


Related articles: What you need to know about cavity wall insulation | Your insulation questions answered | How to convert a basement


What different types of damp are there?


Most damp problems are the result of condensation due to inadequate ventilation and are common in older properties where fireplaces and wall vents have been blocked up and new windows fitted without ‘trickle’ vents. Moisture from breathing, washing, drying and cooking, if not removed, will condense on the coldest surface, typically on walls and windows, especially in closed-off, poorly ventilated rooms that are not heated, such as basements.

Common symptoms include a musty smell, black mould, and surface water. The solution is to improve the rate of air changes in affected areas by adding vents, clearing existing ones and fitting extractor fans.


A leaking roof can cause damp. Rainwater that finds its way in can travel considerable distances across joists, making it difficult to trace the source. However, the route in can be identified by a damp patch on the ceiling, or worse, a collapsed ceiling. Find the leak and repair the roof, plus repair faulty gutters or remove any blockages. Look out for patches presenting inside with paintwork bubbling or wallpaper becoming saturated and peeling off.

Penetrating damp

Persistent or driving rain can quickly saturate external walls. On modern houses, the moisture should never bridge the cavity to reach inside, and with effective protection, any moisture that does penetrate the outer wall should run into a damp proof course, or onto door and window trays, and be channelled away. If these are missing, defective, or if there’s rubble or mortar in the cavity, water can seep across and create damp patches inside.

To rectify, identify the faulty building detail and correct it. In older properties with solid walls (no cavity), penetrating damp is likely due to defective walls, such as worn pointing, slipped or broken tiles, or cracked render or cladding. So, maintain and repair the exterior, or alter the cladding material or add another layer.

Take care not to use modern, impermeable finishes on old houses, such as hard sand and cement, which prevent solid walls from ‘breathing’, worsening damp. For basements, external drainage should be improved and the walls and floors tanked.

Rising damp

Modern buildings with cavity walls should not suffer from rising damp, providing a correctly installed damp proof course is in place. This type of damp can be identified by spotting discoloured patches on walls that darken when it rains.

The ingressing water usually carries dissolved salts from the ground that form crystals on the wall where the moisture evaporates, and once these are present in the walls or plaster, they’ll attract moisture from the air. To prevent the damp, these salts need to be removed and treated.

Plus, you’ll need to check external ground levels, drives or paths have not been built up above the damp-proof course, as this could compromise its effectiveness. If it’s found to be defective, it is possible to introduce a new one into a opening in metre sections at a time, followed by re-pointing – speak to your builder, surveyor or a specialist damp company. An alternative, but less effective, option is to inject a layer of silicone into the walls to close any gaps in brickwork, forming a waterproof layer.

Rising damp is more common in traditional solid-walled properties, where there is no damp proof course. The first course of action should be to remove the source of the moisture by improving ground drainage around outside walls, removing plant growth against walls, and ensuring ground levels are at least 15-20cm below internal floor level. Then, ensure the wall can dry out naturally by restoring lime pointing or breathable render and paint finishes, both internally and externally.


Signs of damp

  • Stained walls or plaster
  • A musty smell
  • Warped wood or damp timber (which, if left untreated, can lead to wet rot)
  • Peeling paint or wallpaper mould
  • Water droplets from condensation
  • Salt deposits on walls, leaving a tide mark

There are a number of steps you can take to limit the extent of the problem:

  • clear gutters and waterways
  • fix leaks
  • add more ventilation
  • install a dehumidifier
  • ensure your damp-proof course is intact

You should also adopt a staged approach to make numerous repairs, starting with the most severe. Making basic lifestyle changes can also remedy small signs, such as seasonal condensation build-up.

If you discover any mould, regular cleaning with a mouldicide wash is vital. Follow the manufacturer’s instructions precisely to remove marks from walls and window frames, and dry-clean any upholstery or clothes where spores have grown. Vacuum cleaning or brushing the mould may increase the disruption of the spores, allowing them to spread and enter the air.

In extreme cases, redecorating may be necessary after cleaning and repairing the causes. A good-quality fungicidal paint will help to prevent mould, while a mouldicide solution that can be added to standard emulsion can also be obtained. When wallpapering, use a paste containing a fungicide to prevent further mould growth.

How much does it cost to repair?

Costs will vary depending on the amount of work required to rectify the signs of damp, as well as the extent of the problem and the type of damp found. Some smaller repairs, which you can carry out yourself, will be relatively low-cost, while treatments for condensation, such as improving ventilation and buying a dehumidifier, may require a larger initial outlay, but will provide long-lasting results.

Penetrating and rising damp are more likely to cost more to resolve, as a specialist’s expertise may be required. Always get at least three quotes from independent consultants and aim to obtain a recommendation, or look for trade body accreditation before employing help.

What to do if you have more than one type of damp

‘You should approach each individual case separately and take the appropriate steps to cure each type,’ advises Rentokil’s Berwyn Evans. ‘Instead of trying to implement a singular, universal solution, which may cause further damage to the property or move the problem to other areas, it is best to treat each damp source as an individual incident.’