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How to deal with damp inside the home?

A damp problem sadly never comes on its own. So it's imperative that it is dealt with swiftly to avoid suffering the detrimental effects on your health, your home and your wallet.. Take a look at the diagram below to put in place the appropriatesteps and to get rid of your damp problem once and for all.

Airing: the first right move

Opening the windows for a few minutes will allow your home to dry. This good habit is particularly effective in winter, as cold air is drier than hot air.

Tip: ventilate briefly but vigorously! Throw the windows wide open for 5 to 10 minutes rather than leave one window ajar all day.

This uses a smaller amount of expensive energy, because it only cools the air and not the large thermal mass of the masonry.

A solution for every problem

Depending on the cause of your damp problem, there are different solutions. The first step is therefore to identify the cause(s) behind your damp problem.

Rising damp: put in a damp course

Symptom: damp on the ground floor, at the bottom of the walls

This problem only occurs on the ground floor up to 1.5 m from the floor. Old buildings are more frequently affected because walls used to be built without a damp course.

Solution: put in a damp course

The only definitive solution is to insert a damp course at the base of the wall, but this is a very big job.
These days people prefer to inject chemical damp proofing at the bottom of the walls. This is still a fairly big job to be handled by a specialist, but the result is satisfactory and the product will do its job for at least 20 years.

Avoid using products that need to be applied onto the wall surface: all they do is mask temporarily the problem without solving it.

Condensation: ventilation

Symptom: condensation on a wall

There is water vapour present in all inhabited buildings: breathing people, pets and plants, cooking, laundry, baths and showers, ironing, etc.

If it is not got rid of, this vapour condenses in droplets on the coldest wall in the room. In the past it always condensed on the windows, but with the introduction of insulated double glazing, windows no longer attract water vapour first. So it then condenses on an uninsulated wall, behind a cupboard, on a thermal bridge or a beam... with all the damage that implies.

This problem is particularly likely to occur in the summer, when the air cools down at the end of the day (see the point below: Ventilation in summer).

Solution: ventilation


There are two options to solve the problem once and for all:

  1. install one or more air extractors in rooms where the most water vapour is generated: some have a heat recovery system for outgoing air;
  2. fit the building with a controlled mechanical ventilation system (CMV) with heat recovery. This can be performed only as part of large-scale renovations.

Click here to find out more about the various ventilation systems.

Rainwater infiltration: repairing leaks

Symptom: rainwater is entering the house

Part of the roof or a ledge is leaking. The drainpipe has a hole in it or is blocked and is "watering" a wall which has become damp.

Solution: repair the leak

It is sometimes difficult to locate the leak because it is can be difficult to see. Also, seepage water can sometimes appear a fair distance away, sometimes even in an adjacent building.

Ventilation in summer is just as important

Warm air can be more humid than cold air, it’s the law of physics. Therefore, during fine weather, the important thing is to aerate the kitchen, bathroom and the entire house. Otherwise, you will find condensation on the walls as soon as the temperature drops, mainly at night. Watch out for mould, encouraged by the heat and darkness behind cupboards and wardrobes and in dark corners!

But how can you ventilate without overheating? Controlled mechanical ventilation (CMV) systems are fitted with an automatic bypass that short-circuits the heat exchanger when necessary. As such:

  • the colder outside air at night is not heated by the outgoing air (as is the case in winter) and the house is cooled to some extent during hot weather.
  • during the day on the other hand, the incoming warmer outside air transfers part of its heat to the outgoing indoor air that is relatively cooler. This avoids overheating whilst ventilating.

Controlled mechanical ventilation can also be fitted with a cooling unit that chills the incoming air and cools the house in summer. But this is not really an air conditioning system.

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