Damp and Mould: Causes and Fixes

Three types of damp

Condensation damp is the most common. Moisture from cooking, washing and breathing hits cold surfaces and forms water, leading to black mould in corners, behind furniture and around windows. Penetrating damp comes in from outside — leaking gutters, cracked render, failed pointing — and shows as damp patches on walls after rain. Rising damp comes up from the ground through a failed or missing damp-proof course and leaves a tide mark low on the wall.

Fixing condensation

Reduce moisture and let it out: cover pans, dry clothes outdoors or with a vented condenser, open windows briefly each day, use extractor fans in kitchens and bathrooms, and keep heating on low rather than off-and-on. Wipe down mould with a fungicidal wash, but it will return unless ventilation improves. A positive-input ventilation (PIV) unit can help a whole house.

• •Use extractor fans and keep them clean.
• •Vent tumble driers to the outside.
• •Keep furniture slightly away from external walls.
• •Heat the home consistently to keep surfaces warm.

Fixing penetrating and rising damp

Penetrating damp is fixed by repairing the outside — gutters, downpipes, pointing, render and flashings. Get a builder to find the entry point before spending money on tanking or membranes. True rising damp is rarer than the other two and needs a new damp-proof course; but many "rising damp" diagnoses are actually condensation or penetrating damp, so get a second opinion before agreeing to injection works.