When a new membrane goes onto a warehouse, shop or office block, the paperwork that arrives afterwards often matters as much as the roof. A warranty certificate looks reassuring, yet three very different promises can sit under that one word: one from the company that made the waterproofing, one from the firm that laid it, and sometimes one from an insurer. They cover different failures, last for different periods and fall away for different reasons.
Owners and managers tend to find out which is which at the worst moment, when a leak appears and the phone calls begin. This guide sets out the three kinds of cover, what each one usually does and does not pay for, how a policy-backed warranty behaves if the roofing firm disappears, and the everyday things that void cover without anyone noticing. It also lists what to ask for before you sign, so the document you receive matches the roof you were promised.
Three promises behind one certificate
The word warranty gets used loosely on commercial jobs, so it helps to separate the promises before you compare anything. Each has a different author and a different test for whether it applies.
What is a material warranty?
This comes from the maker of the membrane, felt, metal sheet or coating. It says the product itself will not fail through a manufacturing fault within a stated period. It does not say the roof will be watertight, because leaks tend to begin at details such as upstands, outlets and penetrations, and seldom across the open field of a sheet.
What is a system warranty?
A system warranty goes wider. The manufacturer agrees to cover the whole build-up it supplied, such as the vapour control layer, insulation, membrane and accessories, provided the roof was laid by an installer the manufacturer is willing to stand behind and was inspected at the end. Whether a particular maker offers one, and on what terms, differs from product to product, so ask for the actual document rather than a summary.
What is a workmanship warranty?
This one comes from the contractor. It deals with how the roof was put together: laps, seams, flashings, falls and the way the membrane meets a wall or an outlet. Poor workmanship is a common cause of early leaks, so this is the promise most likely to be tested in the first few winters. It is only as good as the firm giving it, which is why the later sections look at what happens if that firm is gone. Our commercial roofing page shows the flat roof systems we work with.
What a manufacturer system warranty covers
A manufacturer would not issue a system warranty unless the conditions were tightly drawn. That is not a criticism; it simply means the certificate is a conditional promise, and the conditions deserve a careful read.
What is usually in scope?
Typically the warranty deals with failure of the supplied materials and, depending on the scheme, leaks traced to a defect in the system as laid. Some schemes pay for the repair of the failed area, others only for the replacement material, and some include a share of the labour. The period is stated in years, and cover can step down as the roof ages. The exact wording on what is paid, and what is not, lives in the terms and conditions, not on the front of the certificate.
What is usually out of scope?
Expect exclusions for damage caused by other trades, storm damage, ponding caused by the structure beneath, fire, vandalism, chemical spills and foot traffic beyond what was allowed for. Consequential loss, such as stock damaged by a leak, is commonly excluded from a product warranty altogether. That gap is real for a warehouse or retail unit, and it is worth raising with your own insurer.
Keep a warranty apart from a lifespan as well. For EPDM, a rubber single-ply membrane, GreenSpec puts the expected service life at 20 to 30 years. The cost guide from Less, updated in March 2026, gives 25 to 40 years for GRP, a glass-reinforced plastic coating, and 10 to 20 years for felt. Treat each as a range seen across the trade. A warranty period can run shorter or longer than any of them, and none of them forecasts how your own building will behave.
Workmanship warranties and the firm behind them
A workmanship warranty is a contract term, so it stands or falls on the business that signed it. Three questions tell you most of what you need to know.
Is it in writing, and does it say what it covers?
A verbal assurance or a line in an email is thin protection. A proper document names the property, the roof area, the date of completion, the length of cover and the type of failure included, such as leaks at seams, flashings and outlets. If it says only that the work is warrantyd, ask what that means in practice, who you contact and how quickly someone must attend.
What does the claim process look like?
Look for the steps: notify in writing, allow access for inspection, agree the cause, then repair. Many documents set a time limit for reporting a defect after you notice it. Late reporting is one of the simplest ways to lose a claim that would otherwise have been valid, so keep the contact details where the property manager can find them, not in one person's inbox.
Can it pass to a new owner?
Commercial buildings change hands and tenants change. Check whether the warranty can be assigned to a buyer or a landlord, and whether a notice has to be sent for that to happen. On a leased building, the lease may also say who holds the benefit of roof warranties, so read it alongside the certificate.
Whichever firm you choose, ask to see the wording of its cover before you accept any price. We look at your roof first and then give a single written total, and the cover that goes with it can be explained at that point, while you still have time to ask questions.
Policy-backed warranties and what they change
Some warranties are backed by an insurance policy taken out for the purpose. The reason this exists is simple: a warranty from a small firm means little if the firm closes. A policy-backed warranty tries to keep the promise alive when the contractor has gone.
How does the cover work?
In outline, the roofing firm buys a policy that sits behind the warranty it gives you. If the firm stops trading and a covered defect appears, you claim against the policy rather than the firm. The detail matters a great deal. Ask who the insurer is, how long the policy lasts, whether there is an excess and what has to be proved before it pays out. Ask also whether the policy is in the name of the property or the contractor, as that decides who can claim.
What can still go wrong?
A policy-backed warranty is still a warranty with conditions. It will usually exclude the same kinds of damage as a manufacturer document, and it may require evidence that the roof was inspected or maintained. It does not turn a poor installation into a good one, and it does not remove your own duties as the building owner.
If you are unhappy with how an insurer has handled a claim, the Financial Ombudsman Service is the place to take a complaint, and it is worth checking early whether your organisation is eligible. If your own building policy needs to be told about roof works or a leak, tell your insurer first and keep photos and receipts from any temporary repair.
What voids a flat roof warranty
Most warranties fail through ordinary site life, not through dramatic events. The conditions below turn up again and again, so build them into how the building is run.
Maintenance that never happened
Many warranties expect outlets, gutters and gullies to be kept clear and the roof to be looked at on a regular schedule. Leaves, silt and blocked drains lead to standing water, and standing water is the commonest reason a claim is refused. Keep a simple log with dates, names and photos, and our guide on how often a commercial roof should be inspected helps you set the rhythm.
Other trades on the roof
Aerial installers, air-conditioning engineers, solar contractors and signwriters all walk and drill on flat roofs. A single unprotected fixing through a membrane can void cover over the affected area, or the whole roof if the terms are strict. Control access with a permit system, and have a roofer reseal every penetration. If panels are planned, read our note on solar panels on a commercial roof before anyone drills.
Repairs by the wrong hands
A patch in an incompatible material, or a repair carried out without telling the guarantor, can end the cover. Report a leak, wait for instructions where the document requires it, and keep the repair record with the certificate. Changing the use of the roof, for example turning it into a plant deck or storage, also tends to be excluded.
Reading the paperwork before you sign
The best moment to shape a warranty is before the contract is signed, when the contractor wants the job. Once the roof is down, you are negotiating from a weaker position.
What should you ask for up front?
Request sample copies of the material, system and workmanship documents, not a brochure line. Ask which one applies to your roof and what has to happen at handover for it to be issued. Some schemes need a final inspection by the manufacturer or an independent inspector, and the certificate does not exist until that visit takes place. Put the date for that visit into the programme, and ask who attends it, because a missed inspection is a frequent reason a certificate arrives months late or not at all.
What belongs in the handover file?
Keep the certificates, the product data sheets, as-built drawings showing outlets and falls, photos from before the membrane went down, and the maintenance instructions. When a defect appears three winters on, that file is what makes a claim quick. Ask the contractor to confirm in writing who to call and what to send, and store a second copy off site so that a change of property manager does not lose it.
How does price tie in?
A cheaper quote can mean thinner cover, so compare what each document says rather than the headline number. Check whether any quote includes VAT, which is 20% at the standard rate, and whether scaffold or access is included. Cover also affects who carries the risk when a landlord and a tenant share repair costs, and our page on who pays for commercial roof repairs sets out how that usually works. A written total after a survey gives you a fixed point to hold each document against, and pictures taken on the roof record the condition it started in.
Part of our Commercial Roofing in Crawley & Gatwick
Warranty queries
Does a manufacturer warranty cover a leak at an outlet?
It depends on the scheme. A system warranty may include accessories and details supplied with the membrane, while a material warranty usually covers only the sheet itself. Ask for the terms in writing and check whether leaks at outlets, upstands and penetrations are named, since those are the places flat roofs most often fail.
Is a long warranty period always better?
No. Length matters less than conditions. A shorter warranty with clear wording, a named person to call and no hidden maintenance traps can serve you better than a long one that is voided by a blocked gutter. Read the exclusions and the reporting rules before you compare the number of years.
What if my roofer has closed since the work was done?
Look at the paperwork for a policy-backed warranty, which is designed to carry on when the contractor has gone, and check whether the manufacturer's own cover still applies. Gather the certificate, photos and any maintenance records, then contact the insurer or manufacturer named on the document, quoting the property address and completion date.
