Damp Proof Course Guarantee: What Sellers Need

If your property has had a damp proof course (DPC) installed or re-treated at any point, a guarantee should exist. When you come to sell, that guarantee will be one of the first documents the buyer's solicitor asks for — and its absence can slow down the conveyancing process, trigger additional enquiries, or create complications with the buyer's mortgage lender.

This guide explains what a damp proof course guarantee is, what it covers, how long it lasts, and — crucially — what to do if you cannot find yours or it has expired. For context on the wider issue of selling with damp problems, see our guide on selling a house with rising damp.

What is a damp proof course guarantee?

A damp proof course guarantee is a written warranty issued by the contractor who carried out damp-proofing treatment at your property. It states that the treatment — most commonly chemical injection, where a silicone-based cream or fluid is injected into the mortar course at DPC level to create a new moisture barrier — will remain effective for the duration of the guarantee period, which is typically 20 to 30 years.

If rising damp returns within the guarantee period and the cause is failure of the original treatment, the contractor is obliged to return and carry out remedial work at no charge to the property owner. Where the guarantee is insurance-backed, the insurer steps in if the contractor is no longer in business.

DPC guarantees are associated with several types of treatment:

• Chemical injection DPC — the most common method, where silicone-based compounds are injected into holes drilled in the mortar course to form a new moisture barrier.
• Electro-osmotic systems — titanium wire anodes inserted into the mortar course and connected to a control unit to repel moisture downward through the wall.
• Physical DPC insertion — a new physical barrier is cut into the wall and an impervious material such as polyethylene or stainless steel is inserted.
• Damp-proof membrane systems — cavity drain membranes or tanking applied to internal wall surfaces to manage moisture ingress.

Guarantees may also accompany associated replastering work, where salt-resistant render is applied after treatment to replace plaster contaminated by hygroscopic salts.

What a DPC guarantee covers — and what it does not

What is covered

A standard DPC guarantee covers:

• The cost of re-treatment if rising damp returns to the walls that were originally treated, caused by failure of the contractor's work rather than a new or unrelated problem.
• In many cases, associated replastering costs where specialist salt-resistant render is required because of the treatment failure.
• Labour and materials for remedial work carried out by the original contractor, or a replacement appointed by the insurer if the original company has closed.

What is not covered

DPC guarantees are specifically scoped to the work that was carried out and its failure. They do not cover:

• Penetrating damp from an external source, such as a leaking roof, failed pointing, or defective render.
• Condensation or surface mould, which is a separate phenomenon unrelated to rising damp. For more on this issue, see our guide on selling a house with mould.
• Damp problems in areas of the property that were not part of the original treatment scope.
• Structural movement or subsidence that causes the damp-proof course to fail by creating cracks or settlement.
• Damage caused by the property owner's failure to maintain the property, such as allowing external ground levels to rise above the DPC line, which bridges the treatment.

It is important to understand these limitations when presenting a DPC guarantee to a buyer. The guarantee does not certify that the property is entirely free of damp problems — only that the specific treatment area was addressed by a qualified contractor within the guarantee period.

How long does a DPC guarantee last?

The duration of a damp proof course guarantee depends on the contractor and the type of treatment, but most PCA-registered contractors issue guarantees of 20 or 30 years. Some older guarantees, particularly for treatments carried out in the 1980s and 1990s, may have been issued for shorter periods of 10 to 15 years and are therefore likely to have expired by now.

The start date of the guarantee is the date the treatment was completed, not the date you purchased the property. If you bought the property with a guarantee that was already, say, 10 years old at the time of purchase, you should check how many years of cover remain.

Insurance-backed guarantees: why they matter

An insurance-backed guarantee (IBG) is one where an independent insurer underwrites the contractor's warranty. This matters because damp-proofing companies, like any business, can cease trading before the guarantee period expires. Without insurance backing, a guarantee from a company that has gone into liquidation is effectively worthless.

With an IBG, the buyer or future owner can make a claim directly to the insurer if the treatment fails and the original contractor is no longer available. The insurer will appoint a replacement contractor to carry out any remedial work covered by the policy.

The Property Care Association (PCA) requires member contractors to offer insurance-backed guarantees, which is one reason why buyers, solicitors, and mortgage lenders prefer to see guarantees from PCA-registered companies. When instructing any damp-proofing work before selling, always insist on a PCA-registered contractor and confirm that the guarantee is insurance-backed.

How DPC guarantees transfer on sale

One of the most practically important aspects of a DPC guarantee for sellers is that it should transfer automatically to the new owner on completion of the sale. You do not typically need to notify the contractor, pay a transfer fee, or take any formal action — the guarantee simply runs with the property.

In practice, your solicitor will include a copy of the guarantee in the contract pack. The buyer's solicitor will review it, confirm that it is transferable (which the document should state explicitly), and note it in the report they prepare for their client. If the guarantee is insurance-backed, the new owner becomes the insured party automatically upon becoming the registered owner of the property.

Some older guarantees from smaller contractors may include a clause requiring formal notification of the transfer. If your guarantee has such a clause, your solicitor can write to the contractor or insurer to notify them of the change of ownership. This is a minor administrative step and rarely causes delays.

What to do if you cannot find your DPC guarantee

A lost DPC guarantee is one of the most common issues in residential conveyancing. There are several steps to try before accepting that it cannot be found.

Step 1: Check your conveyancing file from when you purchased

When you bought the property, any existing DPC guarantee should have been included in the contract pack and may be held with the title deeds. Contact the solicitor who handled your purchase and ask for a copy of the conveyancing file. Alternatively, if you have a paper file at home, look for any documents relating to guarantees, warranties, or specialist treatment.

Step 2: Contact the contractor

If you know which contractor carried out the treatment, contact them directly and ask for a duplicate certificate. Most reputable companies maintain records of all work carried out and can reissue copies. Have the property address and the approximate date of treatment to hand when you call.

Step 3: Contact the Property Care Association

The PCA maintains records of guarantees issued by its member contractors. You can contact the PCA at property-care.org with your property address and any details you have about the contractor or treatment, and they can confirm whether a guarantee was registered with them and assist with tracing documentation.

Step 4: Check with your mortgage lender

If you have a mortgage, your lender may hold copies of guarantees with the title deeds. This is less common but worth checking, particularly if you purchased the property recently.

Step 5: Arrange indemnity insurance

If the guarantee genuinely cannot be traced, indemnity insurance is the standard solution in residential conveyancing. Your solicitor can arrange a legal indemnity policy that covers the buyer and their mortgage lender against the risk that the original treatment was defective. Premiums are typically a one-off payment of £50 to £200, and the policy lasts indefinitely, transferring to future owners. Most mainstream mortgage lenders accept indemnity insurance for missing DPC guarantees, provided the policy is from an approved insurer.

For a broader overview of how missing documents of this kind are handled in conveyancing, see our guide on selling a house with missing guarantees.

What to do if the DPC guarantee has expired

An expired guarantee is a different situation from a missing one. Expiry simply means the contractual warranty period has ended. It does not imply the treatment has failed or that damp problems have returned.

In practice, an expired DPC guarantee is unlikely to be a significant obstacle to a sale unless:

• There are visible signs of rising damp in the property that suggest the treatment may no longer be effective.
• A buyer's survey flags moisture at the base of walls and recommends investigation.
• The buyer's mortgage lender specifically requires a guarantee to be in force.

If the buyer is concerned about the effectiveness of an expired DPC, the practical solution is to commission a specialist damp survey from a PCA-qualified surveyor. If the survey confirms the treatment is still performing as intended and there are no signs of rising damp returning, this provides a reasonable level of assurance. A survey of this kind typically costs £150 to £350 and can be carried out before or after a buyer is found.

Alternatively, if damp problems have genuinely returned after the guarantee expired, you may need to consider whether to re-treat the property before selling. See our guide on selling a house with a failed DPC for a detailed look at your options in that situation.

Disclosing DPC treatment on the TA6 form

The TA6 Property Information Form is a key document in the conveyancing process. Section 7 (relating to services, warranties, and guarantees) asks specifically whether any specialist treatments — including damp proofing — have been carried out at the property and whether guarantees were obtained.

You must disclose:

• Whether any damp-proofing treatment has been carried out during your ownership or, to the best of your knowledge, by previous owners.
• The approximate date of the treatment and the name of the contractor, if known.
• Whether a guarantee was issued and whether you hold a copy.
• Whether you are aware of any ongoing damp problems or any failure of the original treatment.

If you do not know whether treatment was ever carried out, say so honestly. If you know treatment was done but have lost the guarantee, disclose that and note that your solicitor is arranging an indemnity policy or tracing the original certificate.

Failing to disclose known damp treatment or misrepresenting the status of the guarantee could expose you to a misrepresentation claim from the buyer after completion. Honesty at this stage, combined with a clear resolution plan, is always the better approach.

What mortgage lenders expect

The UK Finance Mortgage Lenders' Handbook is the standard reference for what mortgage lenders require in residential conveyancing. It does not prescribe a specific requirement for DPC guarantees in all cases, but individual lenders may have their own criteria. In practice:

• Most lenders accept an insurance-backed guarantee from a PCA-registered contractor as sufficient evidence that damp treatment was carried out to a recognised standard.
• Where the original guarantee cannot be produced, most lenders accept indemnity insurance from an approved provider as an alternative, particularly where the treatment is more than a few years old and there are no visible signs of failure.
• Some lenders, particularly for high-value properties or where surveys have flagged damp concerns, may require a specialist survey confirming that the treatment is effective before they will release funds.

The buyer's solicitor will check the specific requirements of their client's lender at the outset of the transaction and advise on what is needed. As a seller, the best position to be in is to have the guarantee ready, or to have your solicitor arrange indemnity insurance early so it can be included in the initial contract pack and does not hold up the transaction.

For a broader picture of how certificates and guarantees fit into the sale process, see our guide on what is a property certificate pack.

Should you re-treat before selling?

If your DPC guarantee has expired and the property shows no signs of damp returning, re-treatment before selling is generally not necessary. There is little commercial logic in spending £1,500 to £4,000 on a new DPC treatment when the existing one is still performing as intended.

Re-treatment makes practical sense in the following circumstances:

• Rising damp has returned visibly — you can see tide marks, peeling plaster, or salt deposits at low wall level — and a specialist survey confirms the original treatment has failed.
• A buyer's survey has flagged active moisture at the base of walls, and the buyer or their lender is requiring treatment as a condition of proceeding.
• The treatment failure is recent enough that the contractor may be liable to carry out remedial work at no cost under any remaining guarantee.

If you do decide to treat the property before selling, ensure the contractor is PCA-registered, that the guarantee is insurance-backed, and that the guarantee period starts from the completion of the new work rather than the original treatment date. A fresh 20- to 30-year guarantee with insurance backing is a straightforward document to hand to a buyer's solicitor.

For guidance on the wider costs involved in preparing a property for sale, including whether pre-sale works offer a good return, see our guide on the hidden costs of selling a house.

DPC guarantees and timber treatment: the connection

Damp proof course treatment is often carried out alongside timber treatment, because rising damp in walls creates conditions conducive to wet rot and woodworm in timbers embedded in or close to damp masonry, such as wall plates, joist ends, and skirting boards.

If your property has had both DPC and timber treatment, you should hold two separate guarantees: one for the damp proofing and one for the timber treatment. Both will be requested by the buyer's solicitor if the TA6 discloses that the work was carried out. For a detailed look at the timber treatment side, see our guide on timber treatment guarantees when selling.

Both types of guarantee are typically issued by the same PCA-member contractor on the same occasion, cover similar periods of 20 to 30 years, and are subject to the same transfer and insurance-backing principles.

Practical checklist for sellers

Before you instruct your solicitor, gather the following information about any DPC treatment at your property:

1. Do you have a written guarantee certificate? If yes, locate it and note the contractor's name, the date, the guarantee period, and whether it is insurance-backed.
2. Is the guarantee still within its coverage period, or has it expired?
3. Does the guarantee document state that it transfers automatically to the new owner?
4. If you cannot find the guarantee, do you know the name of the contractor who carried out the work? If so, contact them for a replacement.
5. Are there any visible signs of damp returning at the base of walls in the treated areas? If yes, commission a specialist survey before marketing.
6. Have you answered the TA6 Property Information Form honestly, including details of the treatment and the current status of the guarantee?

Sources and further reading

• Property Care Association (PCA) — UK trade body for damp proofing and timber treatment specialists. Members are required to issue insurance-backed guarantees. Find registered contractors and access the guarantee database: property-care.org
• BRE (Building Research Establishment) — Good Building Guide 33: Assessment and treatment of rising damp in buildings. The BRE sets UK standards for damp diagnosis and treatment: bregroup.com
• UK Finance Mortgage Lenders' Handbook— The standard reference for what mortgage lenders require in residential conveyancing transactions, including specialist treatment guarantees: lendershandbook.ukfinance.org.uk
• HM Government — Approved Document C: Site preparation and resistance to contaminants and moisture. Building Regulations requirements for damp-proof courses in new and altered buildings: gov.uk/government/publications/moisture-resistance-approved-document-c
• Law Society Conveyancing Protocol, 5th edition — Sets out the standard process for property transactions in England and Wales, including the handling of guarantees and warranties: lawsociety.org.uk
• HomeOwners Alliance — Independent consumer guidance on damp proofing guarantees and selling property with damp treatment history: hoa.org.uk

Related guides

• Roof Guarantee When Selling Your Property
• Cavity Wall Insulation Guarantee

Frequently asked questions