FixMeasure
Basics
Damp and mould at home: causes and fixes
Damp patches and black mould are more than cosmetic: they damage finishes and can affect health. The fix depends on finding where the moisture comes from.
1. Three kinds of damp
Condensation is the most common: warm, moist indoor air meets a cold surface such as a window, an outside wall or a corner and turns to water. Penetrating damp comes from outside through leaks, gutters or cracked render. Rising damp comes up from the ground in walls without a working damp-proof course; it is much rarer than often claimed.
2. Reading the signs
Mould in corners, behind furniture and around windows, worse in winter, points to condensation. A patch that grows after rain points to a leak. A tide mark up to about 1 m above the floor on a ground-floor wall may be rising damp. Fix leaks and gutters first; see Roof area and gutters: measuring and sizing.
3. Prevent condensation
Reduce moisture: use extractor fans in kitchens and bathrooms, put lids on pans, dry laundry outside or in a vented dryer. Ventilate briefly but fully several times a day. Keep rooms evenly heated and leave a gap behind furniture on outside walls. Better insulation raises surface temperatures; see R-value and U-value explained: insulation basics.
4. Cleaning small areas of mould
Small areas, roughly up to 1 m², can usually be cleaned by the occupants: wear gloves, eye protection and a mask, and wipe with water and detergent, then dry thoroughly. Throw away mouldy absorbent materials such as ceiling tiles. Larger areas, mould after flooding, or mould in a home where someone has asthma or a weakened immune system call for professional help.
Common mistakes
- Painting over mould without fixing the cause.
- Drying laundry indoors in unventilated rooms.
- Switching off extractor fans to save energy.
- Blocking trickle vents in windows.
- Assuming every damp patch is rising damp.
Frequently asked questions
What is the most common cause of mould at home?
Condensation from moist indoor air meeting cold surfaces.
Does opening windows help?
Short, full airing several times a day removes moist air without cooling the walls much.
Can I remove mould myself?
Small areas, yes, with gloves, a mask and detergent; get help for large areas.
Does bleach kill mould?
Detergent and water are usually recommended for cleaning; the key is removing the moisture source.
Will insulation stop mould?
It helps by warming surfaces, but ventilation and moisture control are needed too.