The short answer
A commercial roof can have a workmanship guarantee from the roofer and a separate manufacturer warranty on the system, such as a single-ply membrane. Ours is a 10-year workmanship guarantee, in writing. System warranties often run 20 to 25 years for EPDM, but they depend on the product, the installer and upkeep. A guarantee is no forecast of lifespan, and the exclusions matter as much as the headline number.
Two promises on one roof
When a commercial roof is laid, up to three documents can come with it. The first is the contractor's workmanship guarantee, which says that the installer will put right faults in the labour: laps that open, fixings that fail, flashings that were poorly formed. The second is the manufacturer's warranty on the product, which says the membrane, sheet or coating itself will not fail from a manufacturing fault. The third, which is not a guarantee at all, is a lifespan quoted in a brochure.
People often confuse these. A membrane with a 20-year warranty does not promise 20 years without a leak. It promises that the manufacturer will deal with a defect in the material within the terms of the warranty, and those terms usually exclude damage by other trades, ponding, mechanical damage and neglected drainage. Our own workmanship guarantee covers our work for 10 years and is given in writing; it is a separate document from anything the manufacturer issues.
The distinction matters at the point of a leak, because the first question will be whose fault it is. That is why the paperwork should be filed with the building's records, not left in a van.
What manufacturer system warranties tend to say
Published figures vary, and they are not promises about your roof. The Less cost guide (updated 2026) calls manufacturer warranties of 20 to 25 years standard for EPDM, while GreenSpec gives EPDM a typical life of 20 to 30 years and the Building Centre quotes in excess of 25 years. The zinc maker offers a material warranty of up to 50 years, assessed project by project. The longest periods attach to specific products installed to a specification.
Read the small print for the following: who is allowed to install the system, whether a pre-installation inspection or a registration is needed, what the warranty excludes, and whether it transfers to a new owner. Some warranties are void if the roof is altered or if another trade fits plant onto it without proper detailing. Others require periodic inspection and cleaning of outlets. If maintenance is a condition, a missed inspection can weaken a claim, which is one reason a planned maintenance programme is worth considering.
You can ask any contractor for the specific warranty document for the product proposed before you sign anything. If one is not available, ask what the guarantee actually covers and in which document it is written.
What a workmanship guarantee can and cannot cover
A written workmanship guarantee is a promise about the labour. Typical covered faults include laps and seams that open because they were poorly made, flashings that detach, fixings that were wrongly spaced or sealed, and outlets that were not properly connected. It would not normally cover damage caused by someone else, such as a contractor dragging equipment across a membrane, or by events outside the roof's scope, such as storm damage that tears a sheet, or a blocked outlet that nobody cleared.
Ours runs for 10 years, in writing, and applies to the work we do. We do not describe it as insurance, and it is not the same thing as a lifespan or a manufacturer warranty. If a fault appears, you tell us, we look at the roof and photographs, and we fix what is ours to fix. The sensible expectation is that regular inspection and clear gutters and outlets keep the guarantee meaningful.
Ask every contractor the same three questions: what is covered, for how long, and who do I call? A guarantee that does not name its terms is a sales line, not a document.
A guarantee also depends on records. Keep the survey report, photographs and quote together in one folder.
How guarantees interact with the roof system and its age
Different systems come with different expectations, and the age of the roof shapes what a guarantee is worth. A new single-ply roof laid with a membrane warranty and a workmanship guarantee has two layers of cover for the first years. Later, as the workmanship period runs out and the membrane warranty approaches its end, the owner is relying more on maintenance than paperwork. Our guide to single-ply membranes explains how PVC, TPO and EPDM differ as systems, and the commercial roofing page sets out the wider service.
An overlay or a repair on an older roof has a different position. If a contractor patches part of a roof, the guarantee covers the patch, not the rest of the roof. A manufacturer is unlikely to extend a new warranty over an old substrate. That is not a flaw in the paperwork; it just means a repair guarantee is smaller by nature.
For expected life, our answer on the longest-lasting commercial flat roof sets out the sourced lifespans for single-ply, felt and metal, and it is worth reading beside any warranty. For metal sheeting, a quieter fault than a leak can raise questions of its own: see why a metal roof is noisy.
Claims, owners, tenants and what to keep
If a fault appears, act quickly and in writing. Photograph the problem, note the date, and contact the contractor named on the guarantee. If the roof is under a manufacturer's warranty, there may be a notification period and a requirement to let the manufacturer's representative inspect before any repair. Tell the landlord if you are a tenant; the lease decides who has the right to claim. Our answer on who repairs the roof on a leased unit covers that split.
When a building is sold, ask whether the warranty is transferable and whether a notice has to be given to the manufacturer. Buyers' surveyors often ask for these documents, and a missing certificate can slow a sale. Ask the contractor to provide copies of everything at handover, including the specification, the product data sheets and the manufacturer's registration number where there is one.
Finally, a written quote after the survey should show what is included, so you can compare guarantees as well as prices. A lower figure with a thinner guarantee can prove dearer later. You get a single written price for the whole job, so the cost is settled before you commit.