Damp, mould and structural
Damp proofing: do you actually need it?
Damp proofing is work to stop moisture rising or penetrating into a building, most often a chemical damp proof course injected into a wall plus replastering. It is genuinely needed only where rising damp is confirmed. The Property Care Association cautions that it is sometimes recommended for damp that is actually condensation, so get an independent diagnosis first.
- Also known as
- damp proof course (DPC), DPC injection, tanking
- Easily confused with
- condensation control (a different fix), leak repair, ventilation improvement
- How serious
- Moderate: needed only when rising damp is confirmed, so diagnose first
- Typical cost
- Usually no cost for DIY control
How to identify damp proofing
Damp proofing is a remedy, not a problem, so the question is whether you need it. A modern home already has a damp proof course (the visible line of engineering brick or plastic above ground level), so new damp proofing is mainly relevant to older properties where that course is missing, failed or bridged.
Recognise the situation that genuinely calls for it: confirmed rising damp, with a ground-floor tide mark and salting, after leaks and a bridged damp proof course have been ruled out.
Be wary of a quote for injection and replastering issued after a quick visual survey, particularly if the same firm will carry out the work and the symptoms point to condensation.
How serious is it?
Moderate: needed only when rising damp is confirmed, so diagnose first
The risk here is financial rather than structural. Unnecessary damp proofing is expensive and does not solve a problem that was never rising damp, leaving the real cause active.
Where rising damp is genuinely present, leaving it untreated continues to damage plaster, decoration and skirting, so correctly diagnosed damp proofing is worthwhile. The whole value depends on an accurate diagnosis first.
How to fix it yourself
- Rule out cheaper causes before considering damp proofing: condensation, leaking gutters and downpipes, and a damp proof course bridged by raised ground or render.
- Lower external ground or paths sitting above the damp proof course, and remove render that bridges it, as these alone can resolve apparent rising damp.
- Improve ventilation and heating to eliminate condensation, which is misdiagnosed as rising damp far more often than not.
- Get an independent diagnosis before agreeing to injection or tanking, and never sign up on the strength of a free survey by the firm that will do the work.
When to call a professional
- Rising damp has been confirmed independently and a damp proof course needs to be installed or repaired.
- You want a neutral diagnosis from someone who does not also sell the treatment.
Who to call
- An independent damp surveyor or a Property Care Association member for diagnosis, ideally separate from whoever would do the work.
- A Royal Institution of Chartered Surveyors (RICS) member where you want a fully impartial opinion before spending.
Frequently asked questions
Do I really need damp proofing?
Only if rising damp is genuinely confirmed. The Property Care Association warns that damp proofing is sometimes recommended for problems that are actually condensation or leaks. Get an independent diagnosis, ideally from someone who will not carry out the work, before agreeing to injection and replastering.
Why is damp proofing so often oversold?
Because many free damp surveys are done by firms that also sell the remedial work, so there is an incentive to recommend it. A genuinely independent surveyor or RICS member has no such incentive, which is why a separate diagnosis is the single best way to avoid paying for treatment you do not need.
What is a damp proof course?
A damp proof course is a barrier built into a wall near ground level to stop groundwater rising through it. Modern homes have one as standard. In older properties it can be missing, failed or bridged, which is the situation where a new chemical damp proof course may genuinely be needed.
Sources
Editor, HomesAndHedge
Oliver leads HomesAndHedge's editorial coverage of home and garden problems. He researches and writes the plain-English explainers on pests, invasive plants, damp and mould, drainage and wildlife, drawing on guidance from bodies such as the Property Care Association, the RHS and the NHS, and is clear about when a job needs a qualified professional.
Last reviewed: 8 June 2026