You will see how each covering is made, how long two published guides expect it to last, how it copes with foot traffic and repair, and what to settle with a roofer before one is chosen.
A kitchen extension in Birchington, a rear addition in Broadstairs or a garage roof in Westgate-on-Sea: the flat roof on top is a small area that takes a lot of weather. Ask three roofers what to cover it with and you may get three answers, because there is no single best material, only the one that suits the shape, the use and the budget of that roof.
The choice here is between three coverings. GRP, glass-reinforced plastic, is a rigid shell made on site from resin and glass fibre. EPDM is a synthetic rubber sheet, a single-ply membrane, that is stuck down in one piece. Felt, in its modern torch-on form, is a bitumen sheet laid in layers and heated to bond. Each of them can be good, and each of them can be laid badly.
This guide compares them on life, foot traffic and repair, the three points that separate them. If you want to talk about your own roof, our flat roofing service begins with a survey, not a sales call.
Three coverings, three ways to stay dry
The covering is the waterproof skin, and what sits under it matters just as much. All three go over a deck, which is the boarded or sheet surface on the joists, and over insulation and a vapour control layer, a sheet that stops warm, damp air from the house reaching cold surfaces. What differs is how the skin itself is formed.
GRP arrives as liquid resin and glass-fibre matting. It is laid and rolled on site, then finished with a topcoat. When it cures it is one continuous shell with no seams, which is why it suits awkward shapes, upstands and small roofs with several corners. Its rigidity is also its weakness: if the deck below moves, the shell can crack.
EPDM comes in a large sheet. A small roof can often take it as one piece, which leaves few joins, and it moves with the building as the seasons change the temperature of the deck. Its detailing at corners, edges and pipes is done with separate pieces and adhesives, and those are the places to watch for a repair.
Torch-on felt is built up in layers of bitumen-coated sheet, with a flame used to melt the underside and bond it to the layer below. It is the most familiar of the three and often the lowest outlay up front, but it has more laps and more heat-work on the roof than the other two.
How long each lasts, by two guides
Published lifespans disagree, so here are two guides side by side. They are typical ranges for the covering, not promises, and they assume the roof has been laid well and maintained. HomeBuilding and Less both publish lifespans for the three materials, and where they differ, both are shown.
| Covering | HomeBuilding | Less |
|---|---|---|
| EPDM | 25 to 30 | 30 to 50 |
| GRP | 25 to 30 | 25 to 40 |
| Felt | 10 to 15 | 10 to 20 |
EPDM and GRP agree at the low end, felt is the shortest in both, and the guides differ most on how long EPDM goes on. Treat the lower figure as the planning one and the higher as a good outcome, and keep in mind that the skin is just a layer in a build-up. A deck that rots or a fall that holds water will shorten the life of any of them.
Any cover a maker offers on paper is a different thing again. It describes what the maker will stand behind, and it is no forecast of how long the roof lasts, so never set one against a lifespan range. Also remember that these ranges are for the covering alone. Rooflights, pipes and wall abutments are separate details with lives of their own, and they are often where a roof that is otherwise sound starts to let water in.
Our page on flat roof lifespan by material goes into the factors that move these ranges up and down.
Foot traffic and repairs
How the roof will be used decides a lot. A roof nobody visits except for gutter clearing makes different demands from one with a door onto it, a plant pot or a washing line. The table sets out how each covering is usually handled; the exact answer comes from the maker's data for the product being laid.
| Covering | Foot traffic | Repair |
|---|---|---|
| GRP | Hard and walkable | Cut out, laminate again |
| EPDM | Walkway pads advised | Patch bonded on |
| Felt | Marks and scuffs | Patch or cap sheet |
GRP suits a roof people will walk on, such as a balcony or a small terrace, because the cured surface is hard. EPDM is soft by comparison and is kept clear of heavy use, with a walkway of pads or boards laid over it where regular access is needed. Felt takes occasional foot traffic but marks, and its surface can be scuffed by grit under shoes.
Repair is where the materials differ in kind. A split in GRP is ground back and laminated again. A damaged patch of EPDM is cleaned, primed and a patch bonded over it. Felt is cut, dried and patched, or a new cap sheet is laid over a section. With any of the three, the repair succeeds or fails on the dry, clean surface beneath it.
See our pages on repairing an EPDM roof and torch-on felt roofing for the detail of those two.
What the guides say about cost
The figures below come from national guides and are not Castle prices. Which? Trusted Traders (November 2025) puts a 6m x 3m single garage roof at £1,400 to £3,500 in felt and £1,950 to £4,000 where the roof is PVC or EPDM and the boards are renewed, also excluding VAT. MyJobQuote (October 2026) gives between £1,500 and £6,000 to replace a flat roof.
MyJobQuote also gives EPDM at around £60 per square metre. That is an average rate from one national guide, not a price for your roof, so it should never be multiplied by an area and read as a total. Which? notes that prices in the South East, Kent included, tend to run high.
For repairs, Checkatrade (June 2026) gives £120 to £170 per m² for EPDM repairs, excluding VAT, where the rates assume repairs of no more than 3m². That is a repair-rate table for small patches, not a replacement price.
Why the figures spread so widely:
- The roof's size, and the number of corners, pipes and upstands on it.
- The state of the deck below, which only shows once the old skin has been stripped.
- The thickness of insulation needed.
- Access, including scaffold and where waste can be taken.
- The edge details, such as trims, drips and the height of each upstand.
- Whether a warm or cold deck build-up suits the room below.
That spread is why a guide cannot replace a survey. The survey of your own roof comes first, then one total in writing.
The details that matter more than the material
A careful roofer will spend as long on the details as on the covering. BS 6229:2025 is the standard for flat roofs whose waterproofing is a flexible sheet or layered covering, and it applies to all three materials here but not to lead sheet. The 2018 edition has been withdrawn. The finished roof needs a fall of at least 1:80 to drain, and IKO, which makes single-ply membranes, recommends that the roof be designed to a 1:40 fall.
The edges matter next. Trims at the eaves and verges, drip details, and upstands at walls decide whether water runs into the gutter or back under the covering. Outlets need to be sized and placed so that every part of the roof drains, and the covering needs to be dressed neatly into them. Where a rooflight or a pipe passes through the covering, it needs an upstand high enough to keep splashing water out, with the skin turned up and sealed against it. Several of our flat roofing pages go through those; the point here is that a good GRP roof with a badly formed edge will fail before a plain felt roof laid with care.
If an old covering is coming off, Approved Document L treats a renewed waterproof layer as renovation, so insulation is brought up too: 0.35 W/m²K is the threshold in Table 4.3 and 0.16 the improved value, with paragraph 4.13 allowing a relaxation where that is not practical. Thanet District Council's building control team on 01843 577522 can say whether a particular job needs approval.
Choosing for a Thanet extension
There is rarely a wrong answer between the three, only a poor fit. Work through these questions with your roofer:
- Will anyone walk on it? If yes, GRP or a walkway on EPDM.
- Is the shape simple or full of corners? Many corners favour GRP, and a plain rectangle suits a single EPDM sheet.
- How long will you stay in the house? A shorter horizon can justify felt, a longer one points to the materials with the longer ranges.
- What is the deck like? Any covering needs sound boards and a proper fall under it.
- Who will look after it? Every flat roof needs its outlets kept clear and its surface checked now and then, so ask what that means for the covering you choose.
Local weather does not rule any of them out. Met Office averages for Manston, 1991 to 2020, show annual rainfall of about 613 mm and a long-term mean wind speed of 9.86 knots at 10 m, and all three coverings are laid in the south east of England as a matter of course. What matters is that they are fixed and bonded to suit the exposure of your roof. A mechanically fixed EPDM sheet and a fully bonded one behave differently in wind, so ask which is proposed and why.
Ask for the quote to name the covering, the insulation, the edge trims and the outlets, and to be one written total. If two quotes name different materials, ask each roofer to say why theirs suits your roof. The answer will tell you more than the price does.
