The short answer
A single-ply membrane is a factory-made waterproof sheet laid in one layer over insulation on a flat or low-pitched commercial roof. The common types are TPO, PVC and EPDM. TPO and PVC sheets are usually joined by heat welding, while EPDM is a rubber sheet joined with adhesive or tape. Published EPDM lifespans run from 20 to 30 years up to 30 to 50.
The name means one layer of membrane, not one layer of roof. Insulation, a vapour layer and the deck sit beneath it, and the detailing decides how it performs.
The three common membranes
TPO stands for thermoplastic polyolefin, a flexible plastic sheet. PVC is polyvinyl chloride, a similar sheet with plasticisers that keep it supple. EPDM is ethylene propylene diene monomer, a synthetic rubber. In this setting TPO means the roofing sheet, not a Tree Preservation Order.
How do the three differ in the field?
The big practical difference is how they are joined. TPO and PVC are thermoplastics, so the overlap between two sheets is melted together with hot air to make a welded seam. EPDM does not melt, so its seams are glued or taped, and the quality of the bond depends on clean, dry surfaces. All three come in wide rolls, which means fewer joints than felt.
Which one suits a building depends on the roof shape, the amount of rooftop plant, the access, the fire requirements and the detail at edges and penetrations. We look at those facts about your roof, not at a brand, and we explain the reasons for the choice in plain words with photos of the roof beside them.
How the roof is put together
A single-ply roof is a build-up. The deck carries a vapour control layer, then insulation boards, and then the membrane. The membrane is either mechanically fixed through the insulation to the deck, fully bonded with adhesive, or held down by ballast such as stone.
Why do the details matter more than the sheet?
Failures cluster at upstands, outlets, rooflight kerbs, pipes and corners, where the flat sheet has to turn into three dimensions. Pre-formed corners and welded or bonded patches handle those, and the workmanship of each is what keeps water out. A good membrane badly detailed will leak at the first drainage outlet. Ask to see photos of the corners and the outlets on any roof that has been laid, since those are the places a rushed crew cuts corners.
Falls matter too. The current flat-roof standard, BS 6229:2025, still expects a finished fall of at least 1:80 across general areas and internal gutters, and designers aim higher, at 1:40, so the finished roof still reaches 1:80 once the deck has settled and the boards are down. Ponding water points to a problem with the falls, not with the membrane, and a new sheet laid over a ponding roof will pond as well.
How long they last
Lifespans are typical ranges and never promises, and published sources disagree. For EPDM, GreenSpec gives an expected service life of 20 to 30 years, while Less gives 30 to 50 years (last updated 26 October 2026). Take the two together as a range, and treat neither as a guarantee for your own roof. For TPO and PVC, the manufacturer's literature on the exact product in question is the place to look, read with the condition of your deck.
What shortens a membrane's life?
Foot traffic from maintenance staff, poor drainage that leaves water standing, damage when plant is installed, and rushed seams. A protected walkway route to plant, a routine of clearing outlets and a check after any other trade has been on the roof all help.
Your own roof's age is less important than its condition. A well-detailed membrane in good order can outlast a poor one half its age, and the survey, with photos of seams, upstands and outlets, tells you which you have before any decision is made about repair or replacement.
Single-ply compared with other systems
Single-ply sits beside built-up felt, liquid coatings and metal sheet systems. Felt goes on in layers on site, and Less puts torch-on felt at 10 to 20 years, with a good job reaching the top of that and a poor one failing sooner. Liquid coatings go on wet over a sound surface, and our page on liquid roof coatings on commercial roofs sets out where they fit.
Is a membrane the right choice for my building?
It suits flat and low-pitched roofs with many penetrations, since the sheet can be welded or bonded around them, and it suits re-roofs where the insulation is being renewed. It may not suit a roof that is badly out of fall, or a steel-clad shed better served by sheeting.
The visit ends with one written price for whichever system fits, and the reasoning is written out beside the number so a finance director can follow it. Our look at insulated roof panels covers the sheeted alternative, and the overview is commercial roofing. To begin, send a plan or photos of the flat roof, with any rooflights and plant marked.
Membrane questions
Is EPDM the same as rubber roofing?
Yes, EPDM is the synthetic rubber used for rubber roofing. MyJobQuote's guide to rubber roofing gives around £60 a square metre for EPDM (Oct 2026), a domestic yardstick that a large commercial roof can sit well away from. We price after the survey, once access, area and details are known.
Can a membrane go over an old felt roof?
A membrane can be laid over felt when the felt and the insulation under it are dry and sound and the new build-up suits the structure, which is the exception rather than the rule. Wet insulation or a failed deck needs replacing first. A survey, with samples taken where needed, decides whether overlaying is sensible or a strip is the better route.
The full picture: Commercial roofing in Taunton · More short answers