Home Health & Safety A Guide To Damp Proofing Your Home

A Guide To Damp Proofing Your Home


If you live in an old house it is likely there will be some damp problems. Damp can come from a broken or breached damp course, damage to roof tiles, water ingress around windows, leaking pipes, leaking drains or condensation from cooking, showering and general use. With a little know-how you can resolve many problems yourself before the need to hire a damp specialist.

Damp problems can be very costly to fix especially if they have led to wet or dry rot. Tackling a small problem early can save you a huge repair bill later down the line – it can cost around £15,000 to resolve serious problems. Luckily, with a little DIY knowledge you can solve most problems.

Causes of Damp

As mentioned above, there are several causes of damp that can be split into three main groups: rising damp, penetrating damp and condensation. Leaks are a fourth cause, but the way to resolve these is simple – identify and fix your leaking pipes.

Rising Damp

Rising damp is whenever water that is present in the ground is allowed to rise up into the house. The two most common reasons for this is either a damaged damp course or a breached damp course. Damaging the damp course is actually unusual, you have to have had a cowboy builder make a mess of your walls for this to happen. More often than not, the damp course is breached. This is either by a material being placed across the damp course, such as a new render on the house, or by earth, patios or paths being built up higher over the damp course. The solution – remove the structure that has breached the damp course. If it is a damaged damp course, this will need to be fixed by removing mortar and injecting a new one. Of course, some old homes were never built with a damp course in place – people relied on a lot of ventilation and just put up with the damp. Fortunately, most homes have been updated now.

Penetrating Damp

Penetrating damp is when water enters the house structure. The water can be from rainfall, a water supply or damaged drainage. It does not take much water to cause a problem, just one tiny leak in a pipe can result in serious damage, especially if the leak is anywhere near wood – and most older houses are built largely of wood. Although walls in older homes are usually solid (which gives rise to condensation damp problems, see below) the floors, skirting boards and roof structure are all wood.

So, one loose roof tile, or a crack in the render, or a leaking radiator pipe that runs below the floorboards can all cause a growing damp problem.

Condensation Damp

Condensation damp is usually the most common problem today. Over the years people have tried to make their homes more airtight to keep them warmer during the winter. This has involved sealing floors, installing double glazed windows, improving wall coverings with new plaster and multiple layers of paint, and in some cases, even covering up sub-floor air bricks to reduce drafts blowing up through the floorboards.

As a result, condensation in the air has no way to escape. We create a huge amount of condensation every day – just think of all the water on your bedroom windows after a cold night. Add to this moisture from showers, cooking, boiling the kettle and watering plants, and condensation can quickly become a problem.

One reason why condensation becomes a problem is because a house is not heated enough – the warmer the air is, the most moisture it can carry before it condenses to water. People tend to keep their homes warm during the day when they are being used, and then turn the heating off at night. The result is that walls, when poorly insulation, get very cold and moisture in the air condenses on them. This moisture allows mould to grow, which ultimately causes rot.

Older houses often have walls with no insulation at all, which means in winter the wall temperature drops to below the dew point and water droplets form on the walls. This results in mould and is usually seen in the corners of rooms, behind pictures and furniture – wherever there is little or no air flow.

Resolving Damp Problems

All damp problems can be resolved with a combination of ventilation, heat and extraction of moisture from the air. However, this can become very costly. You should always run an extractor fan when using your kitchen or bathroom, ideally with a 30 minute over-run for the bathroom. Also, keep your home heated overnight in winter – set the thermostat to around 17 degrees Celcius to avoid damp problems. Dehumidifiers are very effective as they extract the moisture from the air, however, they are both expensive to buy and expensive to run, so really should only be a short term solution.

Resolving damp caused by structural problems is always complex and time consuming. If a room has that musty smell, you will need at least to remove all furniture and carpets and lift some floorboards to inspect the joists and wall plates – wall plates are the planks of wood that run along dwarf walls under your floor, and joists run across these, which the floorboards sit on. Inspect under your floors to identify causes of damp – check pipes for leaks, look for signs of water entering in specific areas around the walls and prod all timbers with a screwdriver to test for rot. You can see some of the work needed to repair rotten joists here.

If the damp is not under floor, go up into the loft. Look at all the wood for signs of rot and check for obvious gaps in tiles and, if you have it, roof felt. The best time to inspect the loft is during heavy rainfall, armed with a torch. If any water is getting in you should either hear it dripping or see it.

Rising damp can be identified by the tide marks on the walls, which usually rise no more than one metre. If you have this, you really need a damp specialist.

With a little hard work you should be able to resolve most damp problems yourself, but if all your attempts fail, then call in the damp specialists. Most will identify the cause, take remedial action, and supply you with a guarantee for their work so that should the problem come back again, they will return to carry out more repair works under warranty.


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