Tell condensation from rising or penetrating damp

Learn to read damp patches, smells, and patterns so you know if it's condensation, rising, or penetrating damp.

DC-01Learn what each type of damp looks likeCondensation shows as water droplets on cold glass and black mould in corners, on sealant, or on wardrobe backs, and gets worse in cold weather. Rising damp brings a tide-mark or peeling wallpaper low down near the skirting, usually only on ground floor walls. Penetrating damp appears at any height, often after rain, and comes from a fault outside such as a leak or crack. Grab a notebook, torch, and tape measure before you start checking your walls.

1 each · Notebook and pen

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1 each · LED torch

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DC-02Measure how high the damp patch sitsMeasure from the floor to the top of the damp mark. Damp below about 1000mm, especially on a ground floor wall, points towards rising damp. Damp higher up, near a window, chimney, or roofline, points towards penetrating damp or condensation. Write the height and room down so you can compare notes later.

1 each · Tape measure (5m)

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DC-03Check for condensation signsLook for droplets on windows first thing in the morning, steamed-up mirrors, and black mould spots that wipe off easily but come back. Condensation is worse in kitchens, bathrooms, and bedrooms with poor airflow, and it usually improves once you heat or ventilate the room. It rarely smells strongly of damp earth, unlike rising or penetrating damp.

DC-04Check for rising damp signsLook for a tide-mark, crumbling plaster, or white fluffy crystals (called efflorescence) near the skirting board, plus a musty smell. Go outside and check the damp-proof course, a slim line usually about 150mm above ground level, running through the brickwork. Check nothing is piled against the wall above that line, such as a flower bed, raised patio, or render bridging it, as this lets damp climb past the barrier.

1 each · Damp meter (pin-type moisture meter)

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DC-05Check for penetrating damp signs outsideGo outside and look at the wall directly behind the damp patch. Check pointing and render for cracks, gutters and downpipes for leaks or blockages, and the roof for missing or slipped tiles. If you use a ladder to check gutters, keep three points of contact and don't overreach. A patch that grows after rain and shrinks in dry spells is a strong sign of penetrating damp.

DC-06Use a damp meter as a guide, not a verdictPress the meter's pins into the plaster in a few spots around the patch and note the readings. Meters are more reliable on timber than on masonry, and salts, foil-backed wallpaper, or metallic paint can give falsely high readings. Use the meter alongside what you've seen and smelled, not as the only answer.

1 each · Damp meter (pin-type moisture meter)

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DC-07Rule out easy condensation causesCheck kitchen and bathroom extractor fans switch on and actually pull air, and that window trickle vents aren't painted shut or blocked. Check whether laundry gets dried on radiators or a tumble dryer vents indoors without a hose to outside, as both pump moisture into the air. Condensation is the most common and cheapest cause to fix, so it's worth ruling out before assuming worse.

DC-08Decide your next step and tidy upIf signs point to condensation, improve ventilation and heating first and see if it clears within a few weeks. If you see a low tide-mark with no obvious bridging fixed yet, or damp that keeps returning after rain, get a professional damp survey before paying for any remedial work. Photograph the patch with today's date so you can track whether it changes, then wipe down your tools and store them dry.

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