PVC or TPO membrane: what is the difference?

Both are single-ply membranes: a waterproof sheet made in a factory, delivered in rolls and joined on site. Both are thermoplastics, which means the material softens with heat and can be fused. Hot air fuses the seams, so the joint becomes part of the sheet instead of a glued line. Both are normally laid over insulation on a flat or low-pitched roof, and both are held down by mechanical fixings, adhesive or ballast depending on the system, so the sheet itself is only one part of the build-up.

The second material is thermoplastic polyolefin, and PVC is polyvinyl chloride. From the pavement you could not tell them apart, and in many ways the laying methods match. That is why the debate is often more about product than about plastic: a well made membrane from one family can outperform a poor one from the other.

Neither is the same as EPDM, a rubber sheet whose joints are glued or taped. Our guide to single-ply roofing sets the three side by side.

The difference starts in the recipe. PVC is made flexible with additives called plasticisers. Polyolefin is a blend of polymers that gets its flexibility from its own structure. Makers add UV stabilisers, flame retardants and reinforcing scrim to both, and the quality and quantity of those ingredients varies from brand to brand and range to range.

That variation is the reason published comparisons can mislead. A claim that one material is tougher, greener or longer lived rests on particular products, not on the label. Look at the specific membrane's data sheet for thickness, reinforcement, fire classification, resistance to ponding and the term of the manufacturer's warranty, and ask what the warranty requires of the owner.

A lifespan figure for either material is only worth having when a maker commits to it for a named product, in writing, with conditions attached. For comparison, EPDM is published at 20 to 30 years by GreenSpec and 30 to 50 years by Less, which shows how far apart two guides can sit.

On a single-ply roof, most of the quality lives in the welds and the details. A seam welded at the wrong temperature or speed can look fine and fail in the first hard winter. Corners, upstands, outlets and penetrations are cut and welded by hand, and a skilled hand matters more than the plastic being welded.

Ask how the seams are tested. A probe check along every weld is routine good practice, and a contractor should be able to describe it. Ask also who has been trained on the system, since makers often tie a warranty to installers they have approved, and ask to see that arrangement in writing before you sign.

Finishing matters outside the sheet, too. Edge trims, drip details and the junction with the wall need fixing neatly and sealing properly, because a membrane is judged on its edges as much as its field. We build those details to the standard the manufacturer specifies and photograph them before they are covered.

The old roof usually decides more than the brochure does. Wet insulation under a membrane will cause trouble whichever plastic sits on top, so the survey checks for it before anything is specified. Falls come next: BS 6229:2025 keeps a minimum finished fall of 1:80, and a membrane that sits in a pond will age early.

Some old coverings, such as bitumen felt, do not mix well with some new membranes, and a separating layer may be required. Whether a new sheet can go over what is there depends on the build-up and on the maker's rules, and our guide to over-roofing explains the trade-offs.

Fire performance and weight can affect Building Regulations, and the Planning Portal lists a significantly different fire performance or a heavier covering as triggers for approval. Your registered building control approver or the council gives the answer for a commercial building.

Start with three questions of your own, before any contractor offers a view. What is the roof made of now, and is it dry underneath? How much foot traffic and plant will it carry? And what will the maker put in writing for this exact product on this exact roof?

Then ask for two or three named products from different makers, with data sheets, and compare them like for like on thickness, reinforcement, fire rating and warranty terms. Price follows from the area, access, insulation and details, and the survey fixes it. The quote that follows is written and gives one total.

If you are weighing single-ply against other systems, our guide to commercial flat roof systems compares the options. Our commercial roofing work begins with a survey, and photographs of every junction that will need a hand-cut detail.