Quick answer: Not all damp patches have the same cause — condensation appears on cold surfaces and is worst in winter, penetrating damp gets worse after rain and has tide marks at its edges, rising damp appears at the base of walls with white salt deposits, and plumbing leaks appear suddenly near bathrooms or radiators. Do not simply redecorate over a damp patch — painting over damp plaster traps moisture, accelerates plaster deterioration and delays identifying the underlying problem.
A damp patch appearing on a wall or ceiling is one of those things that's easy to ignore at first — and gets harder to ignore the longer it's left. Understanding what type of damp you're dealing with, who is responsible for fixing it, and what to do in the meantime is the starting point for getting it resolved.
What type of damp is it?
Condensation — most common; caused by warm moist air hitting cold surfaces; worst in winter, improves in warmer weather, associated with mould growth on the surface. Penetrating damp — comes through the building fabric from outside through defective pointing, cracked render, failed window seals, blocked gutters or defective roofing; gets worse after rain; may have tide marks at its edges. Rising damp — comes up through the base of walls; appears on lower sections with a tide mark, white salt deposits and a musty smell; less common than it is often diagnosed — many cases attributed to rising damp are actually penetrating damp or condensation. Plumbing leaks — appear suddenly rather than gradually; located near a bathroom, kitchen, radiator, or directly below a bathroom above.
What the law says
England, all rented properties: Homes (Fitness for Human Habitation) Act 2018 — a persistent damp patch the landlord has been made aware of and not addressed is a potential breach. England, social housing: Awaab's Law — investigate within 14 days, complete emergency repairs within 7 days where there is a risk to health. Wales, all rented properties: Renting Homes (Wales) Act 2016 — continuous fitness for human habitation standard across all rented accommodation. Homeowners: identify the source correctly before spending money on treatment — treating the damp patch without fixing the cause is not a solution.
What you can do now
Document it immediately with photographs, note when it appeared, and whether it gets worse after rain or after periods of high indoor moisture. If you rent, report it in writing immediately with photographs; keep copies. Check obvious external causes — blocked or broken gutters are one of the most common causes of penetrating damp. Improve ventilation if condensation is the likely cause. Do not redecorate over a damp patch — the damp must be resolved and the surface fully dry first. If your landlord doesn't respond, contact your local council's environmental health department; they can inspect under HHSRS and require your landlord to carry out works. Be cautious of damp-proofing company surveys if you own your home — they have a commercial interest in diagnosing rising damp.
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