By Chris, owner of Everlast Roofing North West (20+ years on Merseyside roofs) · About Everlast Roofing · Last updated 2026-08-22
Summary
For a garage roof in the North West, EPDM and GRP are both good choices and both will comfortably outlast the felt they are replacing. The difference is in the detail. EPDM is a single rubber sheet laid in one piece, so on a plain rectangular garage there are no seams to fail and it copes well with a roof that moves. GRP is a liquid resin and glass matting that cures into a hard shell, so it handles complex shapes and foot traffic better but it does not like movement. On a simple detached garage I fit EPDM more often than not. On anything with a lot of edges, or a roof someone will walk on, GRP usually wins.
From Chris, the owner
Ask the roofer what the deck is going on before you ask which membrane. Both EPDM and GRP need a clean, dry, solid deck, and on a 1960s garage the existing boards are often chipboard that has been damp for years. Fitting either system over a soft deck wastes the membrane, because the deck will keep moving and the covering will fail early. On a garage the deck is usually the cheaper half of the job, so replace it while it is open rather than saving two hundred pounds and losing the roof.
Most garage roofs I get called to in Liverpool are on their second covering. The original was felt, someone replaced it with more felt in the nineties, and now that has crazed and split and the owner is standing in the garage looking at a damp patch on the boxes. The question is nearly always the same: what should go on it this time, EPDM or fibreglass?
The suppliers will tell you their own product is best, and the search results for this are almost entirely merchants selling membrane by the metre. So here is the installer’s version. What each one actually is, what each costs on a Merseyside garage, where each one fails, and which I would put on your roof after looking at it.
What Is EPDM Roofing And How Does It Work?
EPDM stands for ethylene propylene diene monomer, which is a synthetic rubber. For roofing it comes as a large flexible sheet, typically 1.2mm or 1.5mm thick, cut to the size of your roof before it leaves the merchant.
That single detail is what makes it different from everything else. On a standard single garage of around 3 metres by 6 metres, the EPDM arrives as one piece. It gets bonded to the deck with adhesive, dressed over the edges into trims, and the upstands are bonded up the wall. There are no joints in the middle of the roof at all, which matters because joints are where flat roofs leak.
- It stays flexible. Rubber moves with the deck as timber expands and contracts through the seasons, which matters on a garage that is not heated.
- It handles freeze and thaw. Relevant in the North West, where a wet January does more damage than a cold one.
- No hot works. It is bonded cold with adhesive, so there is no torch and no fire risk near a garage that probably has fuel or a car in it.
- It is quick. A straightforward garage is usually a one-day job once the deck is sound.
The trade-off is that EPDM is a soft covering. It will take occasional foot traffic for maintenance, but it is not the thing to put on a roof that doubles as a balcony or somewhere you store things. If you want more detail on the system itself, our EPDM rubber roofing page covers specification and guarantees.
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What Is GRP Fibreglass Roofing?
GRP stands for glass reinforced plastic, and it is the same material principle as a boat hull. Chopped strand glass matting is laid over the deck and saturated with a catalysed polyester resin, which cures hard within a couple of hours. A pigmented topcoat goes on afterwards.
Because it goes on wet and cures in place, it forms around whatever shape it is laid on. That makes it the better answer wherever the roof is not a simple rectangle.
- It cures seamless. Around upstands, pipes, rooflights and awkward corners, there is no cutting and bonding, the laminate just follows the shape.
- It is hard-wearing. You can walk on a GRP roof without worrying. It suits garage roofs used for storage access or anything with a rooflight that needs cleaning.
- The edges are crisper. GRP trims are bonded into the laminate itself rather than clamped over it, so the finished detail looks sharper.
- It takes a colour. The topcoat can be specified in different shades, which matters if the roof is overlooked from a window.
The trade-off is rigidity. A cured GRP shell does not flex, so if the deck below moves, the laminate can crack, usually along a board joint. That is why deck preparation matters even more with GRP than with EPDM, and why it needs laying over a proper OSB3 deck rather than old chipboard. Our GRP fibreglass roofing page has the full specification.
EPDM Roofing Vs GRP Roofing: The Honest Comparison
Here is the side by side, based on what I actually see going wrong on Merseyside roofs rather than what the manufacturers claim.
| EPDM rubber | GRP fibreglass | |
|---|---|---|
| Realistic lifespan | 25 to 35 years | 20 to 30 years |
| Seams on a plain garage | None, one sheet | None, cures seamless |
| Copes with deck movement | Yes, stays flexible | No, can crack at board joints |
| Foot traffic | Occasional only | Good, walkable |
| Complex shapes and upstands | Workable but more detailing | Better, follows any shape |
| Weather window to install | Wider, adhesive tolerates cool | Narrower, resin needs dry and above 5C |
| Repairability | Easy, patch bonded on | Easy, re-laminate the area |
| Best for | Plain rectangular garage | Complex shapes, walked-on roofs |
The weather window is the one that catches people out in the North West. GRP resin needs a dry deck and a temperature above about five degrees to cure properly, and it needs to stay dry for a few hours afterwards. Between November and March that is not always achievable here, and a resin laid in the wrong conditions will not cure fully. EPDM adhesive is far more forgiving, which is why more of my winter garage jobs go out in rubber.
The lifespan difference is real but smaller than the marketing suggests. Both will outlast felt by two or three times. What decides how long yours actually lasts is the deck underneath and the quality of the edge and upstand detailing, not which of these two you pick.
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EPDM Roofing Cost Vs GRP Roofing Cost In Liverpool
These are the figures I quote around Liverpool and Sefton. A single garage is roughly 18 square metres, a double around 32.
| Job | EPDM | GRP fibreglass |
|---|---|---|
| Single garage, existing deck sound | £1,100 to £1,700 | £1,300 to £1,900 |
| Single garage, new deck required | £1,600 to £2,400 | £1,800 to £2,600 |
| Double garage, new deck required | £2,400 to £3,600 | £2,800 to £4,000 |
| Add insulation while the deck is open | £300 to £700 | £300 to £700 |
| Localised repair to existing covering | £180 to £400 | £200 to £450 |
GRP runs slightly higher because it is more labour intensive on site and the resin is weather-dependent, so there is more risk built into the price. On a plain garage the gap is usually a couple of hundred pounds, which is not enough on its own to decide it.
The number that moves the price most is the deck. Whether it needs replacing is worth more than which membrane you choose, and any quote that does not state clearly whether a new deck is included is not a quote you can compare. Ask for it as a separate line.
One thing worth knowing: adding insulation while the deck is open is cheap relative to doing it later, and on a garage that is being converted or used as a workshop it changes how usable the space is. If that is on your mind, our guide to flat roof conversions in Liverpool covers the structural side.
Which Is Better For A Garage Roof Replacement?
After twenty years of fitting both, this is how I decide on site.
- Plain rectangular garage, no rooflight, nobody walking on it: EPDM. One sheet, no joints, quickest job, and it forgives a deck that moves a little.
- Roof with a rooflight, several upstands, or an awkward shape: GRP. The laminate follows the shape and the detailing ends up tidier.
- Roof used for storage access or as a walkway: GRP. It is the harder wearing surface by a distance.
- Garage attached to the house with a long abutment wall: Either, but the upstand detail matters more than the membrane. Get that specified properly.
- Job going out between November and March: EPDM, unless there is a settled dry spell. Resin and a wet Merseyside winter do not mix.
- Deck is soft or you are not sure: Neither, until the deck is sorted. Budget for boards.
What I would not do is choose on lifespan alone. The published figures put EPDM slightly ahead, but the difference between a twenty-five year roof and a thirty year roof is far smaller than the difference between good and bad edge detailing. I have replaced eight-year-old GRP that failed at a badly formed upstand and I have seen thirty-year-old EPDM still watertight.
We fit both across the area, so whether you are in Bootle, Aintree, Crosby or anywhere else in Liverpool, we will tell you which suits your garage rather than which we would rather fit.
What Are The Downsides Of EPDM Roofing?
Worth answering honestly, because it is the question people actually search and most pages selling EPDM skip it.
- It is soft. A dropped ladder or a sharp edge will puncture it in a way it would not puncture GRP. Easy to patch, but it can happen.
- It looks like what it is. Matt black rubber. If the roof is overlooked from a bedroom window, some people prefer the finish of a pigmented GRP topcoat.
- Bonded edges rely on the installer. The field of an EPDM roof has no joints, but the perimeter trims and the upstands are bonded, and that is where a rushed job shows up in three years.
- It moves underfoot. Not a defect, but people expect a roof to feel solid and EPDM feels slightly springy, which occasionally worries owners who are not expecting it.
None of those are reasons to avoid it on a garage. They are reasons to care who fits it. The membrane is a commodity you can buy anywhere, and the difference between a roof that lasts thirty years and one that fails in five is entirely in the deck preparation and the detailing at the edges.
Whichever you go with, ask for the manufacturer guarantee in writing in your name, and ask for photographs of the deck before the covering went on. If a roofer will not photograph what they covered up, that tells you something. Call Chris on 07933 828 045 and he will look at the garage and tell you which system it wants, with both prices in writing.
EPDM And GRP Roofing Work Across Merseyside
Recent EPDM rubber and GRP fibreglass installations on garages, dormers and extensions around Liverpool. Every job starts with a survey and an itemised written quote.
- EPDM is one rubber sheet, so a plain garage roof has no field joints at all.
- GRP cures hard and seamless, which suits rooflights, upstands and awkward shapes.
- EPDM flexes with a moving deck; GRP can crack at board joints if the deck moves.
- GRP is the walkable option if the roof is used for storage access.
- GRP resin needs a dry deck above 5C, which limits winter installation in the North West.
- Both need a clean, dry, solid deck; budget for new boards on a 1960s garage.
- Add insulation while the deck is open, because doing it later costs far more.
- Get the deck stated as a separate line on any quote so you can compare like for like.
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Twenty years on the roofs of Merseyside. Chris quotes the job and Chris runs the job, photos every step of the way. If the roof has another ten years in it, we will tell you. If it does not, we will show you why in the pictures and give you a written itemised quote with scaffolding, skip, materials and VAT broken out, the lot. Deposit on booking covers materials, balance on completion.
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Frequently Asked Questions
What Is EPDM Roofing?
EPDM roofing is a synthetic rubber membrane, usually 1.2mm or 1.5mm thick, supplied as a single sheet cut to the size of your roof. It is bonded to the deck with cold adhesive and dressed into edge trims, so on a standard garage there are no joints across the field of the roof at all. It stays flexible through freeze and thaw, which suits the North West climate.
What Are The Downsides Of EPDM Roofing?
It is a soft covering, so a sharp impact can puncture it in a way it would not puncture GRP, and it feels slightly springy underfoot. The finish is matt black, which some owners dislike if the roof is overlooked. The perimeter trims and upstands are bonded rather than seamless, so a rushed installation shows up at the edges. None of these rule it out on a garage, but they make the installer matter more than the membrane.
How Much Does EPDM Roofing Cost?
On a single garage of around 18 square metres in Liverpool, EPDM runs £1,100 to £1,700 if the existing deck is sound, and £1,600 to £2,400 if a new deck is needed. A double garage with a new deck runs £2,400 to £3,600. Adding insulation while the deck is open costs a further £300 to £700 and is much cheaper done at the same time.
How Long Does An EPDM Roof Last?
Twenty-five to thirty-five years on a properly prepared deck with good edge detailing. The membrane itself is not usually what fails. What shortens an EPDM roof is a deck that was damp or moving when it went on, or bonded upstands and trims that were rushed. Both are installation issues rather than material issues.
Does EPDM Have To Be Glued Down?
On a domestic garage or extension, yes. The sheet is bonded to the deck with a contact adhesive and the perimeter is dressed into trims. Larger commercial roofs sometimes use mechanically fixed or ballasted systems instead, but on a garage full adhesion is standard because it stops wind uplift getting under the sheet at the edges.
Is GRP Roofing Better Than EPDM Roofing?
Neither is better across the board. GRP fibreglass is harder wearing and walkable, and it handles rooflights, upstands and awkward shapes better because it cures seamless around any shape. EPDM copes better with a deck that moves and can be installed in a wider weather window, which matters through a North West winter. On a plain rectangular garage EPDM is usually the better fit; on anything complex or walked on, GRP is.
How Much Does GRP Roofing Cost?
A single garage in GRP fibreglass runs £1,300 to £1,900 over a sound deck in Liverpool, or £1,800 to £2,600 with a new deck. A double garage with a new deck is £2,800 to £4,000. GRP typically comes in a couple of hundred pounds above EPDM because it is more labour intensive on site and the resin is weather dependent.
Can You Walk On An EPDM Or GRP Roof?
GRP comfortably, EPDM occasionally. A cured fibreglass laminate is a hard shell that takes regular foot traffic without denting, which is why it suits garage roofs used for storage access or roofs with a rooflight that needs cleaning. EPDM will take someone walking on it for maintenance but it is not intended as a trafficked surface, and repeated use will eventually mark it.
For more local roofing advice, browse the Everlast Roofing blog or call Chris on 07933 828 045.
