Damp proofing guarantees, and the six questions the trade next door answers in public
A guarantee is the one line on a damp quote nobody prices and almost nobody reads. What the published terms actually say, what voids one, what it costs, and how it compares with a scheme that puts all of it in the open.
By The Damp GuyLast updated
The short version
Not everything sold as a damp proofing guarantee is the same product. The contractor's own is a promise from a company, commonly 10, 20 or 30 years, and the trade body puts the usual ceiling on one at no longer than ten. An insurance-backed guarantee is a separate policy costing 3% to 5% of the contract value, and one provider's published terms say plainly that damp proofing indemnity can only be claimed upon when the contractor has ceased to trade. So the second one is cover against your builder disappearing, and nothing else. Ask which you are being offered. Then ask the harder question: of the 6 things a guarantee has to answer before it is worth anything, how many can you read before you sign?
The six questions, and who answers them in public
A guarantee is only worth what you can check about it in advance. These are the six things that decide it, set against a guarantee scheme in an adjacent trade that publishes every one of them on its own website.
The comparison is not a like-for-like. The Cavity Insulation Guarantee Agency guarantees cavity wall insulation and has nothing whatever to do with damp proofing. It is here because it is the closest thing in British building work to a published answer sheet: a scheme-level body standing behind member installers, with its terms, its timescales and its claim record all in the open. Hold a damp-proofing guarantee against it and the gaps stop being a feeling and start being a list.
| The question | Cavity wall insulation, as the scheme publishes it | Damp proofing, as it is published |
|---|---|---|
| How many years, and from when? | 25 years, published as a notification window: a claim must be notified within 25 years of the installation date | Commonly 10, 20 or 30 years across the trade, and one provider offers all three. What the clock runs from is set by each contract |
| Does it survive when I sell? | Yes, and no fee is published. The guarantee remains valid for subsequent owners or occupiers of the property | Depends on the document. One insurer publishes an assignment cost of 5% of the original contract value; another makes transfer conditional on the contractor's own guarantee being transferable |
| Is there a ceiling on what it will pay? | Yes, and it is a stated number: the maximum value of rectification work is currently £20,000 | One insurer publishes a claim limit from £2,000 to £500,000 by application, capped at the original contract price. A contractor's own guarantee publishes no ceiling anywhere read |
| What happens when the installer stops trading? | The scheme carries on and directs the complaint to the supplying System Designer | Nothing, unless the guarantee is insurance-backed. The trade body can only mediate against current members, and one insurer states damp proofing indemnity can only be claimed on once the contractor has ceased to trade |
| Who do I escalate to, and how fast? | Eight performance standards in working days, ending in binding arbitration under a scheme approved by the Chartered Trading Standards Institute | The trade body acknowledges a complaint within 5 working days and publishes no resolution timescale, stating it has no legal sanction. One insurer aims to respond within 10 working days of a completed claim |
| Where is the claims record? | Published quarterly on its own website, back to Q4 2015: claims handled, claims resolved, complaint types and arbitration counts | Not published. No provider, insurer or trade body read publishes a claim volume, an upheld rate or a rejected rate |
Read down the last column and the picture is not that damp-proofing guarantees are bad. It is that most of what you would want to know is set by your particular document rather than by a scheme, so there is nothing general to look up and no published standard to hold it to. On one of the six, the claims record, there is no answer published anywhere at all.
That last one deserves a sentence of its own, because it is the sharpest difference. The insulation scheme puts out quarterly statistics going back to Q4 2015. In Q2 2026 it reported 391 claims handled and 297 resolved, and it publishes arbitration counts too. The only arbitration outcomes it has ever printed, in Q3 2025, were 3 published awards of which 2 failed and one succeeded in part. Three cases is not a rate. It is still three more published outcomes than exist for the whole damp-proofing trade.
None of which tells you that a damp-proofing guarantee will not be honoured. It tells you that you cannot find out in advance, which is a different problem and the one you can actually do something about. The rest of this page is what is published, and how to use it.
What a damp-proofing guarantee actually covers
Workmanship, and not new damp from a different cause. That distinction does more work than the number of years does, and it is where most claims go wrong.
A published trade cost reference puts it in one sentence: a guarantee covers the workmanship, not new damp from a different cause, so get the terms in writing, confirm whether it is transferable to a buyer, and keep the certificate. The trade body says much the same from the other side, describing member guarantees as formal commitments that the remedial design and the materials installed meet a stated standard of quality and performance.
Now put that against how damp actually behaves in a house. Water can reach a wall by three routes, and a treatment deals with one of them. If a chemical course was injected and the wall is still wet because rain is crossing the structure, or because warm air is condensing on a cold surface, the work was not defective. It was aimed at the wrong problem, and a guarantee against defective work has nothing to say about that. This is the single most common way a long guarantee turns out to be worth nothing, and it has nothing to do with the company's conduct.
Which is why the cheapest protection on this page is not a guarantee at all. It is establishing what is actually wrong before anybody drills a hole, and who pays for the inspection decides a great deal about what it finds. A guarantee is the last line of defence against a bad job. A correct diagnosis is the first, and it is the only one that stops you paying for the wrong work at full price.
The lengths on offer run from ten years to thirty. One independent commentator on the preservation trade describes the spread exactly that way, and adds the sentence that frames the whole subject: any guarantee is merely a promise from the contractor, so if the contractor fails, for whatever reason, the guarantee is worthless. He also warns, about insurance rather than about any named firm, that some cover is very poor and either covers only the cost of the materials used or carries so many conditions that a claim is impossible. Length is the part that gets advertised. Backing is the part that decides.
Three things get called a guarantee, and they fail differently
A contractor's promise, an insurance policy, and a trade body membership. They are sold in the same breath and they do completely different jobs.
| What it is | What it actually is | When it does something | What ends it |
|---|---|---|---|
| The contractor's own guarantee | A formal commitment by the contractor that the remedial design and the materials meet a stated standard, usually running no longer than 10 years | When you report a defect and the contractor accepts it falls inside the scope | The contractor ceasing to trade. It is a promise from a company, so it lasts as long as the company does |
| An insurance-backed guarantee | A separate insurance policy that honours the terms of the contractor's own guarantee, priced at 3% to 5% of the contract value | Only once the contractor has ceased to trade. Both providers read check that first, and one states it as a clause | The unexpired term running out, a defect outside the original guarantee, or an exclusion. Structural alterations, redecoration and indirect losses are all named exclusions in one policy |
| Trade body membership | Not a guarantee at all. A trade association that audits members biennially and mediates on technical disputes | It does not pay. It mediates, and it acknowledges a complaint within 5 working days | The member leaving. It states it can only mediate in complaints raised against current members, and that it has no legal sanction |
The middle row is the one people misread, and it is worth being blunt about. An insurance-backed guarantee does not give you a better guarantee. It gives you the same guarantee, honoured by somebody else in one specific circumstance. The trade body's own words for it are that it honours the terms of the long term guarantee originally issued to you by your contractor, where that contractor has ceased to trade and is therefore unable to meet their guarantee obligations.
The third row is not a guarantee at all, and nobody selling it says it is. It still gets heard as one on a doorstep, because "we are members of the trade body" arrives in the same paragraph as the thirty years.
The same three-way split shows up on every job in this trade. It is the question behind a twenty year guarantee on timber treatment, where not one source publishing a period states what backs it, and it is the question behind a cellar system whose guarantee depends on an annual service. Same document, three different trades, one question.
The insurance-backed one does not start until the company stops
This is the clause that reorders the decision, and it is published. Read it before you decide whether the premium is worth paying, because it tells you precisely what you are buying.
One provider sets it out in its own published terms: damp proofing, timber treatment, wall tie, lateral restraint and structural waterproofing indemnity can only be claimed upon when the contractor has ceased to trade, unless you hold that provider's standalone guarantee instead. The second provider the trade body names checks the same thing before it will even issue you a claim form, and tells homeowners to contact the original contractor first where that contractor is still going.
So the product is not a second opinion on your damp. It is a contingency against one event. While your contractor is trading, the insurance is inert and you are in a dispute with the contractor, exactly as you would be without it. The trade body is candid about where those disputes land: they arise when the contractor asserts that the defect falls outside the scope of the guarantee.
Two costs sit inside the claim itself and neither is advertised. A claim survey fee is payable when you make a claim, returned in full where the claim turns out to be valid. And one provider requires a claimant to go and get surveys and repair estimates from two local repair companies before it will assess anything. That is unpaid legwork, at the point when you have already discovered your contractor has gone.
The published timescales, for what they are worth: up to seven working days to receive a claim form by post, and an aim to respond within ten working days of receiving the completed form and documentation. Set those beside the 8 standards the insulation scheme publishes and the difference is not that one is slower. It is that one publishes what happens at every step and the other publishes two numbers at the start.
- Acknowledge a concern: within 2 working days.
- Get in touch to arrange an inspection: within 5 working days.
- Send the inspection report and the proposed scope of works: within 27 working days.
- Obtain quotes for the works: within 2 working days of your agreement.
- Complete rectification in a simple case: within 50 working days.
- Complete rectification in a complex case: within 90 working days.
- Respond if you reject the proposed resolution: within 5 working days.
- Implement an arbitration award: within 5 working days.
That list is the insulation scheme's, not damp proofing's, and it is on this page as a demonstration rather than a standard anybody is breaking. It shows what it looks like when a guarantee scheme commits to a clock in public. Nothing stops the damp trade doing the same. Nothing has made it.
What the guarantee costs, and the arithmetic on the fee table
Between 3% and 5% of the contract value, corroborated by two independent sources. The published fee table says something more precise than that, and it is not in the advertised range.
The premium is one of the few genuinely checkable numbers in this whole subject, and two sources agree on it. The provider publishes it as 3% to 5% of the works contract value guaranteed, with a minimum of £100 plus VAT. A trade cost reference, writing for contractors rather than for insurers, puts it at the same 3 to 5 percent of contract value and says it should be offered as a paid option. Two sides of the same transaction, one figure. It belongs on the quote as a line you can see, and on most quotes it does not appear at all.
Then there is the fee table underneath the headline, which is published in bands. Here it is, with the share of each band's own ceiling worked out beside it.
| Contract value up to | Premium, before VAT | Share of the band ceiling |
|---|---|---|
| £2,000 | £100 | 5.0% |
| £3,000 | £150 | 5.0% |
| £4,000 | £200 | 5.0% |
| £5,000 | £250 | 5.0% |
| £6,000 | £300 | 5.0% |
Every band is exactly 5% of its own ceiling. Not roughly. Exactly. Which means the advertised 3% to 5% is not a range you land somewhere inside. It is what you pay at the top of a band, and more everywhere else in it. A contract of £2,100 falls into the next band up and pays £150, which is 7.1% of the contract. A £600 job pays the same £100 minimum as a £2,000 one, which is 16.7%.
Above £6,000 the percentage takes over again. None of this is hidden, and none of it is wrong. It is simply not what "3 to 5 per cent" sounds like, and you can only see it by putting the table next to the headline.
What the premium buys, in terms: cover for 10, 20, 30 years depending on the policy, with underground developments, which have a fixed term of 10 years the stated exception. A claim limit set per application between £2,000 and £500,000, with a yearly aggregate of £500,000, and a damp claim capped at the original Contract Price shown in the Guarantee Schedule. You can only take it out where there is no pre-existing fault or damage present, which is worth knowing if you are shopping for cover after a problem has appeared rather than before.
The second provider publishes no term at all, saying instead that cover varies by product so there is no single term for all of them, and that its policies are paid for by the installer with nothing due from the policyholder. Read that last one with the first source beside it: the contractor pays the insurer, and the contractor is paid by you.
What voids it, and why ordinary building work is the risk
Almost everything published about voiding conditions describes normal life in a house. That is not a trap being sprung. It is what makes a long guarantee weaker than it reads.
Start with the exclusions one insurer publishes on the policy itself: indirect losses, redecoration costs, furniture damage, removal of fixtures, defects arising from structural alterations, and any remedial work not approved in advance. Look at what is on that list. Redecoration is excluded, and redecorating is the entire visible consequence of damp coming back. Structural alterations are excluded, and an extension, a knocked-through wall or a new opening is a structural alteration.
A contractor writing about guarantee length publishes a longer list of the things that unpick a claim, and every item on it is ordinary:
- Work done by someone other than the original team.
- Minor leaks never reported.
- Changes to ventilation.
- Alterations to property structure.
- Unauthorised repairs.
- Claims linked to condensation.
- Problems blamed on maintenance neglect.
Changes to ventilation is the one to sit with. Ventilation is the lever most people reach for when a house feels damp, and it is usually the right lever. Fitting an extractor, blocking a chimney, replacing windows or putting in a positive input unit are all changes to ventilation, and the reader most likely to make one is the reader whose treated wall is still damp. The same clause shape exists in the trade next door: that scheme's guarantee is not valid if the insulation has been altered or disturbed, which ordinary later building work does without anybody meaning to.
Then the transfer question, which catches people at the worst possible moment. Guarantees do not always transfer easily, on the same contractor's published account: many require paperwork, fees, or filing within a set period or before a sale closes. The obstacles it names are missed deadlines, typically 30 to 90 days after the sale, unpaid fees usually between £30 and £75, and proof of inspection logs, or direct registration. On the insurance side the cost is published outright at 5% of the original contract value to assign the policy to a new owner, while the second provider makes transfer conditional on the contractor's own guarantee being transferable at all.
Hold all of that against the yardstick, where the same question gets one sentence: the guarantee remains valid for subsequent owners or occupiers of the property, and no fee is published. If you are the one handing the paperwork to a buyer, find out which of those two shapes your document is before the sale starts, not during it. A landlord who posted the wording of her own twenty year guarantee could not tell from reading it whether the cover survived selling the house. That is not a rare experience. It is the ordinary one.
Who regulates a damp-proofing contractor
In the sense a homeowner means the word, nobody does. That is a statement about published scheme scope, not about anybody's conduct, and it is checkable in about a minute.
The government publishes a list of the categories of building work a competent person scheme can cover. The point of such a scheme is stated plainly: it lets a tradesperson prove their ability to carry out certain work to the required standard, instead of you applying for building regulations approval. Here is the whole list.
- Air pressure testing of buildings
- Cavity and solid wall insulation in an existing building
- Combustion appliances
- Electrical installations
- Heating and hot water systems
- Mechanical ventilation and air-conditioning systems
- Plumbing and water supply systems
- Replacement windows, doors, roof windows or rooflights
- Replacement of roof coverings on pitched and flat roofs
- Microgeneration and renewable technologies
Cavity and solid wall insulation in an existing building is on it. Damp proofing is not, and neither is a damp proof course. That single difference explains a great deal. The insulation scheme can tell a homeowner that where the installer was registered under the competent persons scheme in England and Wales, the certificate also incorporates evidence of compliance with the Building Regulations. There is no damp-proofing equivalent of that sentence, because there is no damp-proofing scheme on the list to write it.
What exists instead is a trade association, and it is straight about what it is. It calls itself the trade body for the industry, it runs ongoing biennial audits of contractor and independent surveyor companies, and it says its role is to mediate between the customer and PCA member to resolve any technical issues. It publishes two limits on that role which are worth reading twice. The first: "The PCA has no legal sanction and any claims for compensation must be addressed through a legal process (Court of law)." The second: "We are only able to mediate in complaints raised against our current members."
Put the second one beside the reason you bought a guarantee. The situation you are insuring against is your contractor no longer trading. A firm that has stopped trading is not a current member. So the mediation route and the failure mode do not overlap, by design, which is exactly why a separate insurance product exists at all.
On timescales the body acknowledges a complaint within 5 working days and its resolution timescale is not published. It states it is unable to provide one. Its complaint record is not published. It states complaints are recorded to track progress and identify potential trends, and publishes no figures from that record.
TrustMark sits alongside it, describing itself as The only Government endorsed quality scheme for work carried out in or around your home and as a not-for-profit organisation operating under a Master Licence Agreement issued by the Government's Department for Business & Trade. Its published escalation runs to an ombudsman once 12 weeks have passed since your first complaint, and it must be taken there within 12 months of that complaint. Worth knowing: the categories its consumer search offers are Energy Efficiency, Interior, Other Repairs & Improvements, Roof, Building Exterior/Garden. There is no damp category among them.
Compare all of that with the regulator next door, which has no damp-proofing counterpart to quote because there is no damp-proofing scheme for one to administer. Asked about complaints on insulation work it funded, Ofgem states its role and then draws the line in one flat sentence: "We do not regulate the insulation industry." Even the trade with a competent persons scheme, a guarantee agency and a published claims record has a regulator saying that. Damp proofing has none of the four.
What to ask, and in what order
You are not going to argue policy wording with anybody. Ask these, get the answers in writing before the work starts, and listen to which ones land awkwardly.
- Is the guarantee yours alone, or insurance-backed? One question, and it decides everything else. If the answer is both, ask which one the years in the advert refer to.
- Can I read the terms before I accept the quote? Not a summary of them, the document. A guarantee you cannot read in advance is a number in a sales sentence.
- What is the premium, and is it on this quote? It is published at 3% to 5% of contract value with a £100 minimum. If you are paying for it, you should be able to see it.
- Does it transfer when I sell, what does that cost, and by when? Three answers, not one. Published transfer costs run from a small administration fee to 5% of the original contract value, and deadlines of 30 to 90 days after a sale are published as a reason claims fail.
- What voids it, as a list? Ask for it written down. Changes to ventilation and structural alterations are both published voiding conditions, and both describe things you are quite likely to do.
- What do I pay to make a claim? A claim survey fee is standard and is returned where the claim is valid. One insurer also expects you to obtain two independent repair estimates yourself.
- And the one before all of them: has the cause been established? A guarantee covers workmanship, not new damp from a different cause. If nobody has confirmed whether the existing damp proof course was bridged rather than failed, the longest guarantee in the trade will not help you.
About this resource
The guarantee terms, the fee bands, the claim limits and the exclusions come from two insurance-backed guarantee providers' own published pages, read on 11 September 2026. Both sell the policy. The definitions of a company guarantee and an insurance-backed guarantee, the claim survey fee and the scope dispute come from the Property Care Association, the trade body for the firms doing this work, as do the complaints procedure and the two sentences about what it cannot do. The premium figure is corroborated by a trade cost reference last updated 29 August 2026. The competent person scheme categories and the Building Regulations wording are government guidance, published free. The comparison scheme throughout is the Cavity Insulation Guarantee Agency, which guarantees cavity wall insulation and does not cover damp proofing.
Four of the ten pages ranking for this term are a named damp company's own guarantee page, and none of them could be read. So nothing here describes what any particular firm guarantees, in either direction. Nothing here says how any provider handles a claim, because nobody publishes that, and one page's unattributed claims table was left out for the same reason. This site does not survey, treat or quote for work. It takes no fee from anyone who does. It cannot tell you what is happening in your building, and a document is no substitute for finding out.
Common questions
Does damp proofing come with a guarantee?
Usually, and the useful question is which kind. A published trade cost reference puts the common terms at 10, 20 or 30 years. The contractor's own guarantee is a promise from a company, and the trade body itself puts the usual ceiling on one at no longer than ten years. An insurance-backed guarantee is a separate product, priced at 3% to 5% of the contract value, and it is the one that does anything once the contractor has gone. Ask which of the two you are being offered, and ask for the terms in writing before the work starts rather than after it.
How long should damp proofing last?
Nobody honest will give you a service life, and this website will not either. No published source worth standing behind puts a lifespan on a damp proof course. What is published is guarantee length, and that is a different measurement: 10, 20 and 30 years are the common terms across the trade, and they say how long somebody is on the hook rather than how long the work holds. The two get confused constantly, usually in the direction that flatters the longer number.
What does an insurance-backed guarantee for damp proofing cover?
It covers the terms of the contractor's own guarantee and nothing wider. Both providers describe it the same way: it honours the long term guarantee the installing contractor issued, where that contractor has ceased to trade. One publishes a claim limit set per application between £2,000 and £500,000, capped at the original contract price, and lists indirect losses, redecoration costs, furniture damage, removal of fixtures and defects arising from structural alterations as excluded. If the original guarantee did not cover something, the insurance behind it does not either.
Are insurance backed guarantees worth it?
That turns on the one event it responds to. One provider states in its published terms that damp proofing indemnity can only be claimed upon when the contractor has ceased to trade. So you are buying cover against your contractor disappearing, at 3% to 5% of the contract, and against nothing else. Two things to weigh before you decide. There is a claim survey fee, returned in full where the claim is valid. And passing the policy to a buyer is published at 5% of the original contract value. Nobody publishes how often the trigger event actually happens, which is the figure that would settle the question.
Do I need a damp proof certificate to sell my house?
Nothing read for this page says you must have one. What the trade does publish is a sequence worth following: get the terms in writing, confirm whether the guarantee is transferable to a buyer, and keep the certificate. Establish the transfer question early rather than during a sale, because it is set by your document and not by custom. One insurer publishes an assignment cost of 5% of the original contract value, and another makes transfer conditional on the contractor's own guarantee being transferable in the first place.
Do you need building regs for damp proofing?
There is no self-certification route for it, which is the part people are really asking about. The government publishes the list of work a competent person scheme can cover, so that a registered installer can certify their own work instead of you applying for approval. Cavity and solid wall insulation in an existing building is on that list. Damp proofing is not, and neither is a damp proof course. Whether your particular job counts as building work is a question for your local building control body, and nothing here answers it for you.