Damp is the household problem that costs the most to ignore and is most often treated as the wrong thing. Almost every failed damp job starts by attacking the mould instead of the water feeding it.
Three causes, three different fixes
- Condensation. By far the most common. Warm, moist air meets a cold surface and the
water comes out of the air onto the wall or glass. The fix is ventilation, heating and insulation, not a damp-proof course.
- Penetrating damp. Water getting in from outside through a failed gutter, a cracked
render, a blocked air brick or a slipped tile. The patch is usually localised and gets worse after rain.
- Rising damp. Genuinely rare, and vastly over-diagnosed by people selling injection
treatment. It shows as a tide mark up to about a metre with salt deposits. If someone offers a free survey and then diagnoses rising damp, get a second opinion from an independent surveyor who is not selling the remedy.
Telling them apart is mostly timing. Condensation is worse in cold weather and on cold surfaces. Penetrating damp is worse after rain. Rising damp does not change much either way.
Dealing with condensation, which is most of it
- Produce less moisture. Lids on pans, dry clothes outside where you can, vent the
tumble dryer properly.
- Get it out. Extractor fan on during a shower and for fifteen minutes after. Window
open a crack when cooking. Trickle vents unblocked.
- Keep surfaces warmer. A cold external wall condenses first. Low background heat
across the day beats short blasts of high heat.
- Leave a gap behind furniture on external walls so air can move.
Removing mould that is already there
Wear gloves and a mask, open a window, and do not dry-brush it, which puts spores in the air. A dedicated mould remover or a diluted bleach solution on hard surfaces works. Never mix it with anything else, see household chemicals. On porous surfaces like plaster or fabric the mould has roots and cleaning the surface is cosmetic.
If you rent
Damp in a rented home is your landlord's problem to fix where it is caused by the building, which covers most penetrating and rising damp and a good deal of condensation caused by inadequate ventilation or insulation.
- Report it in writing and keep a copy. Photographs with dates.
- Keep a note of when it appears and after what, which is exactly the evidence that separates
the three causes above.
- If nothing happens, your council's environmental health team can inspect and require works.
Do not stop paying rent to force the issue. It weakens your position and can put your tenancy at risk.