Condensation is damp that is generated inside the home. When you cook, shower, dry clothes indoors or simply breathe, the air fills with water vapour. When that air touches a cold surface, the vapour turns into droplets, just as it does on a glass of cold water in summer.
If it happens every day, the wall is always damp and mould appears. It is one of the most common types of damp and also one of the most poorly treated, because waterproofing does not fix it.
How to recognise it
- Black mould in corners, where the wall meets the ceiling and behind wardrobes and furniture.
- Steamed-up windows and droplets on the window frames in the morning.
- It gets worse in winter and in the least ventilated rooms.
- It mainly affects walls that face outside or onto lightwells.
- It does not depend on rain.
Why it happens
Lots of vapour
Kitchens without extraction, bathrooms without a window, clothes dried indoors or many people in a small space.
Poor ventilation
Homes that are not aired, or new windows that seal so well that the air is no longer renewed.
Cold walls
Uninsulated walls and thermal bridges at pillars, slab edges and around windows, where the vapour condenses.
What works to get rid of it
- Ventilate more and better: open the windows every day, use the cooker hood and the bathroom extractor fan and, when that is not enough, install controlled mechanical ventilation, which renews the air continuously; with heat recovery, you do not lose warmth.
- Warm up the walls: insulate cold walls and eliminate thermal bridges. From the outside, with external wall insulation (ETICS); from the inside, with insulated wall lining when the facade cannot be touched.
- Improve the windows: well-insulated frames keep the glass warmer and reduce condensation on it.
- Clean and protect mouldy surfaces with a fungicidal treatment, once the cause has been resolved.
What does not work: waterproofing the facade or the roof, or simply painting. Anti-mould paint and dehumidifiers help, but only as a complement.
Condensation in buildings and interior lightwells
In old buildings, narrow interior lightwells and poorly ventilated common areas are frequent sources of mould. In a building in Ciutat Vella we improved ventilation in the common areas, treated the surfaces with fungicide and proposed insulating the coldest walls: mould growth fell significantly.
Why it pays to act
Mould is not just a cosmetic problem: it aggravates allergies, asthma and other respiratory conditions, spoils paint, plaster and furniture, and makes a home feel cold even with the heating on.
We diagnose and treat condensation in homes and buildings. First we confirm that it really is condensation and not water ingress or rising damp, and then we propose the solution that actually gets rid of it.
From Viladecavalls (Barcelona) we work across Spain and on international projects.
Have a similar project?
We visit you, assess the building and give you a detailed, no-obligation quote.
Frequently asked questions about condensation
Why does mould appear in corners and behind furniture?
Because they are the coldest and least ventilated spots in the room. Water vapour in the air condenses there and the constant moisture lets mould grow. Corners on external walls and slab edges are the typical spots.
Why have I had condensation since I replaced my windows?
New windows seal very well and eliminate the draughts that used to refresh the air, so the vapour generated in the home stays inside. You need to compensate with ventilation: open the windows every day or install mechanical ventilation.
Does anti-mould paint solve condensation?
Not on its own. It cleans and protects the surface, but if ventilation is still poor and the walls are still cold, the mould comes back. It is applied after the cause has been resolved.
Does a dehumidifier help?
It helps lower the humidity in the air while it is switched on, but it does not get rid of cold walls or poor ventilation. It is a support, not the solution.
