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Many homes have minor problems with mould on window sills often caused by condensation on windows on cold mornings. However more extensive damp or mould can be a serious problem for the structure of the building, your clothes and your furniture and for your health. Mould spores can be a serious irritant to the lungs.
Dampness can have any of three causes
Rising damp can affect any wall in contact with the ground and therefore can affect internal as well as external walls. It normally does not rise above about 1 metre in height and you will usually see a characteristic ‘tide mark’. Below the tide mark the plaster below feels cold or damp to the touch. In other respects it can look similar to penetrating damp
Rising damp is caused by a problem with your damp proof course. Either
In the last case, you need to remove the material that is bridging the course. Otherwise, you need a specialist to fix the damp proof course.
This type of damp can affect almost any location in the home and is usually the result of a building or plumbing fault allowing water to enter e.g., through holes in the roof; spilling from blocked guttering; around window frames; through cracked/leaky pipes; overflows. If you think you have a problem with penetrating damp it is advisable to have the fault rectified as soon as possible. With more extreme weather, heavy, wind-driven horizontal rain can penetrate right through mortar joints to the inside face of the wall.
If the damp comes through to the inside of a plastered wall then you can get 'blown' plaster. This happens because water in the wall dissolves salts in the material and then when it evaporates off the surface the salts crystalise out. The crystals push the plaster out of the way. You will need to fix the source of the problem, wait for the wall to dry and then replaster.
Condensation usually occurs during cold weather, whether it is raining or dry, and it does not leave a tidemark. It appears on cold surfaces and usually forms in places where there is little movement of air, e.g. corners of rooms; on or near windows; in or behind wardrobes/cupboards/window blinds; on north-facing walls. It usually affects properties during the months of October to April when home ventilation is at its lowest. During this period you tend to close windows and doors, thus allowing moisture levels to build up.
Condensation is caused by a combination of high moisture levels and/or cold areas.
To reduce moisture levels you need to reduce moisture sources and ensure you have good ventilation. Moisture can come from:
So you need ventilation but you don't want draughts. Our ventilation page has more advice on this, but here are some suggestions
The other approach to fixing condensation is to avoid cold areas. That means keeping the whole house warm. Insulation will make this easier - make sure there aren't any gaps. See our insulation advice page. However:
If you have mould you need to treat it as well as fixing the cause.
First wipe down walls and window frames with a fungicidal wash, which carries a Health and Safety Executive approval number. Follow the instructions precisely. Dry-clean mildewed clothes and shampoo carpets. If you disturb the mould by brushing or vacuuming this can increase the risk of respiratory problems.
After treating the mould you will need to redecorate. For paintwork it is a good idea to use a fungicidal paint but this won't work if you cover it with ordinary paints and wallpaper. If you are wallpapering, use a paste containing a fungicide.