Single-ply is the name for a waterproof membrane made in a factory as a single sheet, then laid on the roof and joined into one continuous skin. It is the standard answer on many larger flat roofs, because the sheets arrive in wide rolls, go down quickly and have few joints compared with layered felt. Three materials dominate: PVC, TPO and EPDM. They look similar from a distance, but they behave differently under heat, around chemicals and at the joints, and the sensible choice follows the building rather than the brand. This guide explains what each membrane is, the three ways of fixing it, how the seams are made, the typical lives and costs we can source, and the checks that decide whether single-ply suits your roof. It is aimed at the owner or manager of a warehouse, shop, office or school block who is weighing up a new membrane.
What single-ply means, and why it is used
A single-ply system has one layer of waterproofing, not several. That layer sits over insulation, which sits over a deck of steel, concrete or timber. A vapour control layer usually goes between the deck and the insulation so that warm, moist air from inside cannot condense within the roof. The membrane sits on top and carries the weather.
The attraction for larger roofs is practical. Sheets can be made in widths of a metre or more and rolled across a roof in long runs, so there are fewer joints than on felt, and the factory controls the thickness and quality of the sheet. The membrane is lightweight, which matters on an older steel frame. It also suits roofs with plant, rooflights and outlets, because it can be cut and shaped around them.
Detailing is where the skill lies. A large clear field of membrane is simple to lay, and the same product around a dozen outlets, a plant plinth and a stepped parapet is a different job. The sheet has to be cut, formed, welded or taped and tested at every change of direction, and every junction is a possible entry point for rain. Ask any installer how the corners and penetrations will be made, not only which membrane they plan to use.
Single-ply is not the only choice. Layered bitumen felt, covered in our page on built-up felt roofing, remains common, and some owners prefer it for its proven track record. The decision is rarely about which material is better in general. It is about which one fits the roof, the budget and the use of the building below.
PVC, TPO and EPDM compared
All three are flexible sheets, but they come from different chemistry.
PVC
Polyvinyl chloride membrane is reinforced with a polyester or glass fleece and carries plasticisers that keep it flexible. Seams are welded with hot air, which fuses the sheets into one. It resists many chemicals and has a long record on commercial roofs. It is not compatible with bitumen, so a separation layer must sit between PVC and any old felt beneath it.
TPO
Thermoplastic polyolefin is a newer family, also welded with hot air. It is reflective, widely used for its light colour and typically free of the plasticisers found in PVC. Because products differ from one maker to the next, the specific membrane matters more than the label.
EPDM
EPDM is a rubber compound, made in very large sheets that can occasionally cover a whole roof in one piece. It is flexible, copes well with movement and temperature change, and is joined with tapes or adhesives rather than heat. Its black surface warms in the sun, and the seams and corners rely on the quality of the adhesive and the workmanship.
| Membrane | Joined by | Typical life (sourced) |
|---|---|---|
| PVC | Hot-air weld | 20 to 30 years (GreenSpec); 20 to 40 (Building Centre) |
| TPO | Hot-air weld | About 20 to over 35 years, depending on the product |
| EPDM | Tape or adhesive | 20 to 30 years or more |
Those lifespans come from GreenSpec and the Building Centre. The sources disagree, which shows how much the particular product and the quality of the installation matter, and why we quote them as ranges. They are typical figures, not guarantees. If a membrane carries a BBA certificate, it is worth reading it for the specific product.
How a single-ply roof is fixed down
There are three ways to hold the membrane to the roof, and each suits a different building.
Mechanically fixed. Screws and plates are driven through the sheet laps into the deck. This is quick, it works on most decks, and it suits roofs where adhesive would struggle. The number and spacing of fixings depend on the wind loads on that building, which are calculated for its height, location and exposure. Edges and corners need more fixings because wind uplift is greatest there.
Adhered. The membrane is stuck to the insulation with adhesive. There are no fixings through the sheet, which gives a smooth surface and spreads wind load across the whole roof. It needs a clean, dry, compatible substrate and good weather during laying.
Ballasted. The sheet is laid loose and held down by a layer of stone or paving slabs. It is simple and protects the membrane from the sun and from impact, but the structure must carry the extra weight. This is a question for a structural engineer, not a roofer.
Whichever method is chosen, the quality of the details matters more than the open field. The upstands (the vertical turn-up at a wall, parapet or rooflight), the corners, the outlets and any penetrations are where leaks start. Good installers form these carefully, with pre-formed corners and welded flashings, and they test the seams before they leave.
Falls, drainage and insulation underneath
A single-ply membrane is not a reason to forget about drainage. Ponded water speeds up the weathering of a membrane, gathers dirt and loads the structure. Guidance based on BS 6229:2018, quoted by manufacturers such as IKO, gives a recommended minimum fall of 1:80 for a flat roof, and suggests designing to 1:40 so the finished roof still drains after construction tolerances and deflection. Those figures are a design reference rather than a promise on any one roof.
On an older flat roof with ponding, that can mean adding tapered insulation to create falls, or altering the outlets so the water leaves. This work adds to the cost, but it addresses the cause of the problem rather than the symptom. Our page on commercial roof costs explains how such items change a quote.
The insulation does several jobs. It keeps the building warm, it provides a firm substrate for the membrane and, in a tapered form, it shapes the falls. If the existing insulation has become wet, it must come out. Laying a new membrane over wet board only traps the moisture, and it returns as damp ceilings and condensation. Where an old roof is being renewed, checking the insulation is part of the survey. Our guide to commercial roof inspection sets out the ways of doing so.
Typical costs, and what they leave out
Published prices here are scarce. What exists is one contractor's reply on MyJobQuote's question and answer pages (31 July 2026), so read these as low-confidence typical UK ranges per square metre, installed.
| System | Typical UK range |
|---|---|
| Single-ply PVC or TPO | £100 to £140 per m² |
| EPDM | £90 to £130 per m² |
| Extra for new insulation | About £20 to £40 per m² |
Our quote is fixed once the survey is done. The ranges leave out several lines that are common on commercial jobs: scaffold or edge protection, removal of the old covering, replacing wet insulation, creating falls, new rooflights, upstand repairs and outlets. For the full picture of how those are handled, see our guide to what commercial roofing costs.
A membrane priced slightly higher by the square metre may suit the building better, and over a long life the difference is small beside the cost of access and preparation. The more useful question is what each system offers for the use of your roof: foot traffic from maintenance, solar mounts, plant or a roof terrace.
Looking after a single-ply roof
A single-ply roof needs less attention than a felt one, but not none. Outlets and gutters should be cleared every year and again after storms, so that leaves and debris do not hold water against the membrane. Seams, upstands and the sealed edges of penetrations deserve a look during the same call, since an open seam costs far less to close early.
Foot traffic is the main cause of avoidable damage. Engineers servicing plant, contractors fitting cables and anyone carrying tools can puncture or scuff a membrane. Walkway pads or a marked route to the plant keep that traffic on protected ground. Sharp tools, solvents and hot work near the roof should be controlled, because some membranes react to oils and fuels.
Repairs differ by material. PVC and TPO can be patched with a welded piece of the same sheet, while EPDM is repaired with tape or adhesive and a patch. Matching the repair to the membrane, and recording it, saves confusion for the next visit. A planned programme is described in our guide to commercial roof maintenance.
Is single-ply right for your roof?
Single-ply suits many commercial roofs, but not every one. The checks that matter are the condition and type of the existing layers, the structure beneath, the fall to the outlets, the amount of plant and penetrations, the foot traffic expected and the fire and wind requirements of the site. On a listed or historic building, a visible membrane may also raise consent questions that need answering before work is priced.
Safety shapes the method too. A single-ply roof often has rooflights, and their fragility is a hazard for anyone working on it. Our guide to fragile roof safety covers the precautions. After installation, regular inspection of seams, outlets and upstands keeps small problems small, and the record of those inspections is useful evidence if a guarantee claim is ever needed.
When we survey, we examine the roof closely, probe the insulation where we can, photograph what we find and recommend the simplest sound option. If a repair is enough, we price the repair. A written price, fixed, comes after that visit, and it states the membrane thickness, how it is fixed and how the edges and outlets are finished. The wider range of work is on our commercial roofing page.