The short answer
Rising damp is groundwater drawn up through the base of a wall by capillary action, usually because the damp-proof course is missing, has failed or is bridged. The classic sign is a horizontal tide-mark up to about a metre, with salt staining and perished plaster low down. Treatment normally means installing a new chemical damp-proof course and re-plastering, but rising damp is genuinely uncommon and frequently over-diagnosed — so confirm it first.
Rising damp is the most talked-about and the most over-diagnosed form of damp. True rising damp does exist, but many homes labelled with it actually have condensation or penetrating damp. This page explains what rising damp really is, the signs that point to it, how it is properly treated, and why an independent diagnosis is worth its weight in gold.
Rising damp at a glance
- Cause Groundwater rising by capillary action
- Usual reason Missing, failed or bridged DPC
- Classic sign Tide-mark up to ~1m, salt staining
- Treatment New chemical DPC + re-plaster
- Typical cost £300–£1,000+ per wall
- Note Often over-diagnosed — confirm first
What causes rising damp
Walls in contact with the ground can draw moisture upward through the tiny pores in brick and mortar, like water climbing a sponge — this is capillary action. Most homes built since the late 19th century have a damp-proof course (DPC): a physical barrier near the base of the wall that blocks this rise. Rising damp occurs when that barrier is absent (in older properties), has broken down, or is bridged — for example by raised external ground or a path above DPC level, a render skirt carried down over it, or debris in the cavity allowing moisture to track across. Bridging is a frequent culprit, and removing it can sometimes solve the problem without any new DPC at all.
Signs of rising damp
- A tide-mark — a roughly horizontal stain, typically no higher than about a metre, where the rise stops.
- Salt staining — white, fluffy or crystalline deposits (hygroscopic and efflorescent salts) carried up from the ground.
- Perished plaster and skirting — crumbling, blown plaster and decaying timber skirting low on the wall.
- Damp, cold feel low down that does not vary much with the weather, because the source is the ground rather than the air or rain.
How rising damp is treated
Where rising damp is genuinely confirmed, treatment usually involves installing a remedial damp-proof course — most commonly a chemical DPC injected into the wall to create a water-repellent band — followed by hacking off and renewing the salt-contaminated plaster with a suitable system. Any bridging must be removed first: lower raised ground, clear the cavity, or remove a render skirt. Re-plastering matters because old plaster holds hygroscopic salts that keep drawing moisture from the air even after the wall itself dries, which is why simply skimming over it tends to fail.
| Step | What it involves | Typical cost |
|---|---|---|
| Survey | Confirm rising damp; moisture profile | £150–£350 |
| Remove bridging | Lower ground, clear cavity, cut render | Varies |
| New DPC | Chemical injection course | £300–£1,000+ per wall |
| Re-plaster | Salt-resistant replastering & drying | Included / extra |
A whole-house damp-proofing job commonly falls in the region of £2,000–£5,000, depending on the number of walls, access and re-plastering. Reputable contractors usually offer a long guarantee on a chemical DPC, and the work can take some weeks to complete and the walls months to dry fully.
What rising damp is not
Several problems are routinely mistaken for rising damp. A plumbing or central-heating leak can keep the base of a wall wet exactly like rising damp; condensation behind a cold, furniture-covered wall can mimic it; and old hygroscopic salts left in plaster from a long-cured problem can keep a wall reading “damp” on a meter even when the masonry behind is dry. A competent surveyor distinguishes these by building a moisture profile up the wall and checking for salts, rather than relying on a single surface reading. This is why a diagnosis from an independent assessor — not from the firm hoping to sell you the treatment — is the safest first step.
Get it confirmed first
Because genuine rising damp is uncommon and the remedy is intrusive and costly, an independent diagnosis is essential. A qualified surveyor — ideally RICS-regulated or a PCA member, and ideally one not also selling the treatment — should confirm rising damp and rule out cheaper-to-fix causes before any DPC is installed. This page is general information, not a site-specific survey.
Told you need a damp-proof course?
Before agreeing to a new DPC, get an independent RICS or PCA diagnosis. Rising damp is over-diagnosed, and the wrong treatment is an expensive mistake.
Frequently asked questions
How high does rising damp go?
Capillary rise is generally limited to around a metre above ground level, which is why a horizontal tide-mark at roughly that height is a classic sign. Damp higher than that usually has another cause.
Is rising damp common?
No. Genuine rising damp is relatively uncommon and is frequently over-diagnosed. RICS and the PCA recommend ruling out condensation and penetrating damp before treating for rising damp.
Can I treat rising damp myself?
Removing bridging, such as lowering raised ground, can help, but installing a chemical DPC and salt-resistant re-plastering is specialist work. Confirm the diagnosis with a surveyor first.
How much does rising damp treatment cost?
A damp-proof course is often £300–£1,000+ per wall, with whole-house jobs commonly £2,000–£5,000 including re-plastering, depending on the property and access.
Sources & further reading
- RICS — Investigation of moisture and its effects in traditional buildings
- Property Care Association (PCA) — Rising damp and remedial damp-proof courses
- gov.uk — Housing Health and Safety Rating System (HHSRS)
- NHS — Can damp and mould affect my health?
This guide is general information, not a site-specific survey, medical advice or legal advice. Damp and mould should be assessed by a qualified surveyor, and health concerns discussed with a GP or the NHS.