What guarantee should a new flat roof come with?

A workmanship guarantee is the roofer's promise about their own work: the laps, the upstands, the outlets, the edge trims and the finish. If a seam opens because it was badly stuck, that is a workmanship matter. A manufacturer warranty is the maker's statement about the membrane itself, usually under defined conditions and often only if the installer is on the maker's list.

The distinction matters because a leak can start from either source and the answer to who pays differs. Where the membrane fails inside its warranty, the maker deals with it. Where a detail around a rooflight or a wall abutment fails, the cause is almost always workmanship. Without both documents, you may not know where to turn.

A guarantee is only worth the paper if it is written down. Look for the term in years, the address of the roof, a description of the work, the date of completion and the name of the firm. It should say what is covered, what is excluded and how to make a claim.

Plain exclusions are normal. Damage from foot traffic on a roof never built to be walked on, a blocked outlet left uncleared or alterations by another trade are fair limits. Vague wording is a warning sign worth taking seriously in either document, as are guarantees that depend on you paying for annual visits you were never told about. Our own workmanship guarantee runs for 10 years and is given in writing. That is our own promise about our own work, and it should not be confused with an insurance policy.

Less, a roofing cost guide updated in March 2026, notes that manufacturer warranties of 20 to 25 years are standard for EPDM, the single-sheet rubber membrane. EPDM life is quoted at between 20 and 30 years or more by other sources, and the warranty is a statement about the product, not a forecast for your roof. You will find the same logic in our answer on EPDM rubber roofs.

Read the small print on conditions. Warranties commonly apply to the membrane only, may require registration by the installer, and may not cover the deck, the insulation, the drainage or damage from other causes. A long warranty on a membrane that was fitted over a poor deck is of limited use. Ask who registers it, how and when the certificate reaches you, and whether it passes to a buyer if you sell the house. Ask too which parts of the roof it names, because a warranty that mentions only the membrane leaves the deck, the insulation and the outlets without cover.

Some documents look reassuring and say very little. Be wary of a certificate with no address, no start date or no named firm. A promise that lasts "the life of the roof" is not a term, because nobody can say how long that is. A guarantee that disappears if you ever have a gutter cleaned, or a satellite dish fixed, is more about avoiding claims than meeting them.

Check whether the guarantee is tied to a particular set of materials. If the quote names a membrane, an insulation board and a deck type, the paperwork should name the same ones. When what was fitted differs from what was written down, a claim becomes a dispute about the roof's identity before it is ever a dispute about the leak.

Finally, ask whether the firm will still be reachable in year eight. A phone number, a postal address and a named contact on the paperwork are small things that make a large difference later.

Put these questions to any roofer, in writing if you can.

• How long does the workmanship guarantee run, and who stands behind it?
• Does the membrane carry a manufacturer warranty, and who applies for it?
• What does each document exclude?
• How do I make a claim, and who do I contact?
• Will you list the materials, thicknesses and insulation on the paperwork?

It is reasonable to hold back final payment until the documents are in your hands. Keep the signed quote, the final invoice, the guarantee and any warranty certificate together, with a note of the date the roof was finished. If the work needed Building Regulations approval, keep that certificate too, because it belongs in the same folder, as our guide to how long a flat roof lasts explains in its section on care.

Even a well-worded guarantee is only as strong as what sits behind it: a sound deck, correct falls, proper outlets and details finished by hand. BS 6229 recommends a design fall of 1:40, with 1:80 as the finished minimum. A roof that ponds will test any membrane, and ponding is often a design or deck issue rather than a fault in the sheet.

The survey photographs your roof as it stands and records the condition of the deck and the drainage, so the written quote can cover the repairs. That also gives the guarantee a clear starting point. If you are choosing between systems, our answer on single-ply PVC for a house looks at one membrane and its warranty position.

For the wider picture, the flat roofing page sets out each system and what the survey covers.