EPDM, GRP or felt: choosing a flat roof material

The table gathers what the published sources say. Where the table shows no figure for a life, no national guide we have read gives one, and we do not fill gaps with guesses.

Prices: MyBuilder, updated 21 August 2026. Lives: Less (updated March 2026), GreenSpec and the Building Centre. The sources disagree on EPDM, which ranges from 20 to 50 years depending on who is asked, so we use the cautious figure and treat anything longer as a bonus. Lead, at £150 to £200 and above per m², is mostly kept for small features and details.

The rest of this guide takes each system in turn and then matches them to the buildings you are likely to be roofing.

Torch-on felt is bitumen felt in rolls, laid in layers. The 'torch-on' part describes how the layers are stuck together: a gas torch heats the underside of the roll until the bitumen softens, and the roll is pressed down onto the layer below. A modern roof is normally two or three layers, a base layer, a cap sheet with a mineral finish, and sometimes a middle layer for extra thickness.

Where it works

Felt is the lowest-priced option in the published ranges and has the longest track record on British houses. It copes well with simple shapes: a rectangle with a few outlets is the right job for it. It is also easy to repair, because a patch of felt can be heated onto an existing layer.

Where it struggles

The weak points are the laps and the details. Less puts a well-laid felt roof at around 20 years and a poorly laid one at under 10, and that gap shows how much rests on whoever holds the torch. Blisters can form if moisture is trapped between layers. Long exposure to the sun makes the surface brittle. A roof with lots of upstands, rooflights and pipes gives the felt a lot of cut edges to seal, which is where leaks tend to start. Applying heat near timber is a risk to manage, which is why some roofers choose a cold-applied or self-adhesive felt on roofs close to eaves or boarding.

Felt suits a simple outbuilding or a garage roof where cost matters and the shape is plain. It is a weaker choice for a complex extension roof with many penetrations.

EPDM is a synthetic rubber supplied as a single sheet, which is why it can often be laid with no join at all across a small roof. GRP is glass-reinforced plastic: matting is laid on the deck, saturated with polyester resin and finished with a top coat, so the roof sets as one hard shell. Our dedicated comparison of EPDM against GRP weighs the two directly. Here is how they sit among the others.

EPDM in the field

EPDM is flexible, which is its great advantage. It follows small movements in the deck and does not crack as the building shifts with the seasons. It comes in a grey-black finish that suits most extension roofs, and it is a good fit for a roof that is mostly flat sheet with few joins. Repairs use patches and a special tape or adhesive, which are simple to apply but do need a clean, dry surface. A big sheet needs a calm day to lay, because wind can lift it during adhesion.

GRP in the field

GRP is hard-wearing and walkable, and a cured roof has no joins. That makes it a sensible choice for balconies and small roofs with awkward shapes, where every corner can be formed in one piece. The trade-off is rigidity: where the deck flexes or the building moves, a rigid shell can crack at the stress point. The deck beneath has to be firm, dry and properly fixed. GRP also depends heavily on the conditions at the time of laying, because resin needs to cure in the right temperature and be kept dry. Repairs are possible, but matching an old top coat to a new patch needs care.

Single-ply PVC is a thermoplastic membrane, supplied in rolls and welded at the overlaps with hot air so the seams become part of the sheet. GreenSpec gives PVC a typical life of 20 to 30 years, and the Building Centre quotes 20 to 40 years for the group of single-ply products, so the figure depends on the product. MyBuilder's range is £95 to £140 per m².

What PVC does well

PVC is made in a good range of colours, comes with preformed corners, outlets and upstands, and handles details well. That matters on roofs with many penetrations, where a welded patch is cleaner than a sealed lap. It can be bought with a reinforcing layer inside, so it resists puncture. Because the sheet is welded, the overlaps are not reliant on adhesive, which is a point in its favour on a complex roof.

What to weigh up

PVC needs a trained installer with welding equipment, and a fitter who has not worked with the system before is a risk. Hot-air welding must be done in suitable conditions. The finish is a thin sheet and it is not designed to carry regular foot traffic unless a walkway is specified.

Liquid-applied coatings

A liquid system is brushed or rolled onto a prepared surface, then cures into a continuous skin with no laps. It is mostly used to renew an existing roof that is sound but weathered, and it can be a way of extending life without stripping everything. It relies on the old roof being dry, well adhered and structurally sound, and it adds no insulation, so the Part L position has to be checked separately. We have not found a national cost or life figure we are willing to cite, so a liquid roof is priced after the survey. Our guide to what a new flat roof costs, in pounds per square metre, covers the other four systems in more detail.

The right covering follows the building. A few common cases show how the choice tends to go.

Extensions

Extension roofs often combine a parapet, an upstand against the house wall, a rooflight or two and a couple of rainwater outlets. EPDM and single-ply PVC both handle that mix well. GRP is a good fit when the shape is irregular or the roof is small. Felt can work if the budget is tight and the detailing is kept simple. The layers underneath count for as much as the top sheet, and our guide to warm, cold and inverted flat roofs explains how the layers sit.

Dormers

A dormer's flat top is usually small and awkward, with cheeks (the side walls) that call for lead or a lead substitute. A one-piece EPDM or GRP top gives few joins, and lead at the cheeks gives a long life where it meets the walls. Lead is expensive, but on a small area the total stays modest.

Balconies and walk-on roofs

Anywhere people will walk, GRP is the usual choice because it is hard. EPDM can be used with a walkway or paving on pedestals. A thin membrane on its own will wear if it is trodden daily.

Garages and outbuildings

Here felt is common because cost is the main factor and the roof is simple. EPDM is a close alternative if the owner wants a longer life from the same area.

Existing details

If the new covering has to meet an old stone wall, a parapet or a previous lead flashing, we check how the join will be formed before choosing. If the house is listed or sits within a conservation area, ask Stroud District Council's planning team whether the look of the covering is a concern.

The covering is only the top layer. Under it are the vapour control, insulation and deck, and the choice of material is limited by what sits there. EPDM and PVC can be laid over insulation boards; a GRP roof needs a firm board deck. Felt can be fixed to a range of surfaces, though not all insulation boards suit torching.

Fire performance and weight

The Planning Portal lists two triggers for approval: a covering with a significantly different fire rating, and one that makes the roof 15 per cent or more heavier. For most flat roofs both tests pass easily, but a heavy ballast, a green roof or paving on a roof that was designed for less can fail the second. Our guide to flat roof Building Regulations sets out the full list.

Insulation and falls

Replacing the waterproof membrane means renovating a thermal element, which brings in the U-value targets under Part L. Whatever material is chosen, the roof also needs proper falls so that water drains and does not stand. A covering is not a cure for a deck that holds water.

We give the written quote after the survey, and our workmanship guarantee runs for 10 years in writing. Any product guarantee from the manufacturer is separate and the quote shows which is which.