Chemical damp-proof course (DPC) injection, the standard treatment where a wall's original damp course has genuinely failed or is absent, typically costs £600–£1,200 on a single wall in a small terrace in 2026, rising to £1,000–£2,500 for a full external wall run on an ordinary 3-bed semi, salt-retardant replastering included. A mechanical or physical damp course — a plastic strip or slate inserted into a cut mortar joint rather than a chemical injected along a drilled line — runs roughly £700–£2,300 depending on wall length. A full damp-proof membrane retrofit, the option usually specified where neither of those will hold, costs £2,500–£7,500.
None of those figures is the one worth starting with, though. Before any of them, there's a cheaper question: is the ground outside actually built up above your damp course, is an air brick painted or bricked shut, is a downpipe splashing water against the base of the wall on every hard rainfall? Those checks cost nothing beyond a walk round the outside of the house, and putting right what they turn up sometimes solves what looks exactly like rising damp for the price of clearing a gulley or lifting a flower bed — not a four-figure injection bill.
I diagnose damp for a living. I don't inject chemicals or cut mortar joints for a living, so I've no stake in which of the figures above you end up paying, or whether you pay any of them at all. What follows is 2026 pricing across the methods actually used, plus the cheap external checks I'd want ruled out before anyone drills a hole in your brickwork.
The short answer
Figures below were checked on 1 August 2026 against MyJobQuote, Checkatrade and MyBuilder's 2026 cost guides, cross-referenced against several damp-proofing specialists' own published price lists — the same set of trade sources behind my damp proofing cost guide. As with most trades in this series, Kent, Sussex, Surrey and London trend above the national figures quoted here, by roughly 15–25% on some specialists' own regional pricing.
| Job | Typical cost (2026) | What's included |
|---|---|---|
| Independent damp survey (PCA/CSRT) | £150–£400 | Diagnosis before any treatment; a RICS survey runs £400–£800 |
| Chemical DPC injection, single wall | £600–£1,200 | Injection plus salt-retardant replaster, small terrace |
| Chemical DPC injection, whole house | £1,000–£2,500 | Full external wall run, ordinary 3-bed semi |
| Mechanical / physical damp course | £700–£2,300 | Plastic strip or slate, walls chemical injection can't reliably treat |
| External remedial works | £300–£1,500 | Ground levels, air bricks, drainage — often the actual fix |
Whichever method ends up specified, treat the injection or insertion price as only part of the bill. Making good afterwards — replastering with salt-retardant renovation plaster to about a metre up the wall, new skirting and redecoration — typically adds a further £300–£800 for a single affected wall, more if flooring or a wider area needs attention, and it's routinely left off the figure a contractor quotes verbally rather than in writing.
What drives the price
Wall length, not house size. You're paying for linear metres of wall treated, not square footage of house. A small terrace with a long run of affected wall can cost more to put right than a larger detached house with a short one.
Which method is actually needed. Chemical injection is the cheapest and most common default. A physical damp course costs more per metre because a mortar course has to be cut out in sections rather than drilled and filled; a full membrane retrofit is pricier again because it's a bigger, more disruptive job. Which one is right depends on the wall, not the quote — more on that below.
Making good. Salt-contaminated plaster has to come off and be replaced with a renovation-grade plaster before redecoration, and that labour, not the injection itself, is usually the bigger line on the final bill.
Access. Render, external cladding or a solid floor abutting the treated wall all add cost, because they need removing before treatment and reinstating afterwards.
Region. Kent, Sussex, Surrey and London trend above the national figures quoted here, in line with most trades in this series.
The cheap fix worth trying before you pay for injection
A genuine damp-proof course sits low in the wall, typically a couple of courses of brick above external ground level. If a path, patio, raised flower bed or a few decades of accumulated garden soil have crept up over that line, the wall is being bridged — damp is getting in above the damp course, not through a failed one — and no amount of chemical injected below it will touch the problem. Checkatrade's 2026 figures put digging back and re-laying gravel at roughly £450 per metre for a small house, rising past £2,000 per metre if a concrete path has to come out; MyJobQuote's drainage-channel figures for the same kind of job run £240–£510 for one wall and £380–£1,400 for a whole house, more again with paving reinstated. Set against a £1,000–£2,500 injection bill, it's the fix worth ruling out first, not last.
The same logic applies to air bricks. Suspended timber ground floors rely on a clear run of underfloor ventilation, and a single air brick painted over, rendered across, or blocked by a flower bed does more to cause damp and rot than most homeowners realise, at essentially no cost to clear. A downpipe discharging straight against the base of a wall instead of into a proper gulley, or guttering that overflows in heavy rain, will keep a wall wet indefinitely and can mimic rising damp closely enough to fool a moisture meter, without a failed damp course anywhere in sight.
None of this replaces a proper diagnosis — I've set out the fuller picture, including how often "rising damp" turns out to be something else entirely and what the RICS, Historic England and PCA joint position statement says about it, in my damp proofing cost guide. The short version here is just: check outside the wall before paying to treat inside it.
Chemical injection vs a physical damp course
Chemical injection — a cream or gel forced along a line of drilled holes near the base of the wall — is the default because it's the cheapest and least disruptive of the three main methods, and it works reliably on standard brick, whether solid or cavity. A physical or mechanical damp course, where a continuous plastic strip or a course of slate is inserted into a cut-out mortar joint, tends to get specified instead on thick rubble-filled walls, stone construction, or older solid walls where a chemical's saturation and continuity through the full thickness of the wall can't be reliably guaranteed. It's more disruptive to install, because the wall is being physically cut into rather than drilled, which is part of why it often costs more per linear metre even though total whole-house figures can land in a similar bracket once a smaller property's wall length is factored in.
Electro-osmotic and magnetic-field systems — using an electrical charge or wiring rather than a chemical barrier — are a further option, generally reserved for listed or solid-wall properties where a standard chemical injection risks doing more harm than good to the wall's ability to manage moisture; I've covered the per-metre pricing for those in more detail on the damp proofing guide linked above. A full membrane retrofit sits above all three in cost and disruption, and gets specified where the wall condition rules the others out, such as badly deteriorated brick or a wall adjoining a basement or cellar.
None of these is an upgrade on the others in the way a more expensive boiler might be. The wall dictates which is appropriate, and a specialist quoting one without explaining why over the alternatives is worth a second opinion.
What I'd watch for in a quote
- An independent survey first, from someone with nothing to sell — a PCA member with CSRT or CSSW qualification, or a RICS surveyor — rather than a free survey from the same firm quoting the treatment.
- External causes ruled out and written down: ground levels, air bricks, gutters, downpipes and render, checked and excluded before injection or a physical course is proposed.
- The method named and justified, not just "damp proofing" as a single catch-all line on the quote.
- Per-metre pricing broken down separately from making good, so you can see what you're paying for the treatment itself versus the plaster, skirting and redecoration.
- PCA membership and an insurance-backed guarantee that survives the installer going out of business.
- No pressure to sign on the day. A legitimate specialist doesn't need a same-visit signature.
Questions I get asked
How much does rising damp treatment cost? In 2026, chemical DPC injection typically costs £600–£1,200 on a single wall in a small terrace, and £1,000–£2,500 for a whole external wall run on an ordinary 3-bed semi, replastering included. A physical damp course runs roughly £700–£2,300, and a full membrane retrofit £2,500–£7,500. An independent survey to establish which of these you actually need is £150–£400.
How do I know if it's actually rising damp? Genuine rising damp is confined to roughly the bottom metre of a wall and tends to leave a tide-mark and salt staining. Condensation, the far more common misdiagnosis, shows up as black mould in corners and on cold external walls, and no damp course touches it because the moisture isn't coming from the ground. I've set out the fuller diagnosis picture in my damp proofing cost guide.
Is a physical damp course better than chemical injection? Not better, just suited to different walls. Chemical injection is cheaper and less disruptive, and works well on standard brick. A physical damp course tends to get specified on thick, rubble-filled or stone walls where a chemical cream's continuity through the wall can't be reliably guaranteed. The wall dictates which is appropriate, not a general preference for one over the other.
Can I fix rising damp without injecting anything? Sometimes, if the real cause sits outside the wall. Ground levels built up above the damp course, a path raised against the brickwork, a blocked air brick or a downpipe splashing the base of a wall are all genuinely cheap fixes that can resolve what looks exactly like rising damp without any chemical or physical course going in. A proper diagnosis should rule these out before injection is ever proposed.
If a survey or a contractor's quote has flagged rising damp and you'd like an independent read on what's actually causing it before anyone drills into the wall, that's exactly what my building survey work is for — and if you're selling, a Home Insight Survey puts the same answer on the table before a buyer's surveyor finds it for you. Call 07946 618203 or get in touch and I'll give you a straight answer before you spend the money.
Small print. This guide is general information, not advice on a specific property, and it doesn’t replace a proper survey and quote for your own home. Prices were researched and correct to the best of my knowledge on 1 August 2026; costs move and vary by region and property. Always get at least three written quotes, and get an independent diagnosis before agreeing to any chemical or physical damp-proofing work.