Why Cape Town homes get damp in winter, and how to fix it

Damp is the most common complaint we hear from Cape Town homeowners in winter. Peeling paint at the bottom of walls, a musty smell in a bedroom, black spots on a ceiling: they look similar, but they have different causes. Treating the wrong one wastes money, so the first step is to work out which kind you have.

1. Rising damp

Rising damp is groundwater drawn up into a wall from below. It happens when a wall has no damp-proof course (DPC), the DPC has failed, or soil, paving or plaster has been built up above it so that moisture bypasses it.

Signs: a tide mark up to about a metre high, salts blooming on the plaster, and paint or plaster that crumbles at skirting level. It is usually worst on ground-floor walls and often gets worse in winter, when the water table rises.

Common causes in Cape Town: older houses built without a proper DPC, flower beds or paving laid against the wall above floor level, and walls plastered right down into the ground.

What fixes it: first, lower the ground level outside so it sits well below the DPC, and make sure paving falls away from the house. Then remove plaster that is contaminated with salts, install a new DPC if needed (often a chemical injection in older walls), and re-plaster with a suitable render. Painting over damp plaster with “damp-proof paint” alone does not work for long.

2. Penetrating damp

Penetrating damp is rain getting in from outside. Cape Town’s winter rain arrives sideways with the north-westerly wind, so walls that face north and west take most of the punishment.

Signs: damp patches that grow after rain and dry out in dry spells, often around windows, at the top of walls under a parapet, or on ceilings below a flat roof or balcony.

Common causes: cracked plaster, failed sealant around windows and doors, missing or blocked weep holes, failed flat roof waterproofing, blocked gutters and downpipes, and parapets without proper capping.

What fixes it: finding the entry point, which sometimes takes a hose test, then repairing it. That might mean re-sealing window frames, repairing cracks and repainting with a good exterior system, fixing flashings or redoing the roof waterproofing (see our flat roof guide).

3. Condensation

Condensation is moisture from inside the house: cooking, showers, drying washing, gas heaters and people breathing. It settles on the coldest surfaces.

Signs: water on windows in the morning, black mould in the corners of ceilings and behind cupboards, often in bedrooms and bathrooms. It is worst in houses that are closed up tightly in winter.

What fixes it: ventilation and warmth. Extractor fans in bathrooms and kitchens that are ducted outside, opening windows for a short time each day, not drying washing indoors, avoiding unflued gas heaters, and adding ceiling insulation so the ceiling is not the cold spot. Mould should be cleaned with a suitable treatment before repainting.

Why it matters to fix it properly

Damp ruins finishes, damages timber floors and joinery, and mould is bad for health, particularly for children and anyone with asthma. Most damp problems we see have been “treated” more than once with paint or a quick patch. A proper diagnosis costs very little compared to repainting every winter.

How we approach it

When we look at a damp problem, we check the outside ground levels, the walls, the roof and the gutters before deciding anything. Often there is more than one cause. If you have damp you cannot get rid of, get in touch and we will come and have a look.