If you've got a flat roof on your extension, garage, or bay window, there's a good chance it was originally covered in felt. And if it's more than 10 years old, there's an even better chance it's starting to blister, crack, or leak. So when it comes time to replace it, what are your options — and which one is actually worth the money?
The Problem with Traditional Felt
Let's start with what most people already have. Traditional bitumen felt has been used on flat roofs for decades. It's cheap, quick to install, and does the job — for a while.
The problem is that felt roofs have a limited lifespan. Most felt flat roofs last between 8 and 15 years before they start to deteriorate. UV exposure causes the felt to dry out and crack. Puddles of standing water accelerate the breakdown. Thermal movement — the roof expanding in summer and contracting in winter — causes the seams to split. Once water gets in, you're looking at damaged decking, damp walls, and potentially ruined ceilings.
We see this constantly across Stafford, Stoke-on-Trent and Congleton. A homeowner calls us because their garage roof is leaking, and when we get up there, the felt is in bits. It's been patched with silicone and roofing tape half a dozen times, but the underlying material has simply reached the end of its life.
Option 1: GRP Fibreglass
GRP (Glass Reinforced Polyester) fibreglass is our recommended choice for most flat roofs. Here's why:
- Lifespan: 30–50 years. A properly installed GRP roof will last decades. It's an entirely seamless system, which means no joints or seams to fail.
- Completely waterproof. The fibreglass creates a single, continuous shell over the entire roof surface. Water literally cannot penetrate it.
- UV and weather resistant. GRP is highly resistant to UV degradation, meaning it won't crack or blister in the sun the way felt does.
- Low maintenance. Once installed, a GRP roof requires virtually no maintenance. An occasional clean is all it needs.
- Aesthetic finish. GRP roofs have a clean, smooth, professional finish in a choice of colours — typically grey, which looks smart and modern.
The downside? Cost. GRP fibreglass is more expensive than felt upfront. For a typical garage, you're looking at £2,000 – £3,500 compared to £800 – £1,500 for felt. But when you factor in the lifespan — 30+ years vs 10 years — the cost per year of use makes GRP significantly cheaper in the long run.
Option 2: EPDM Rubber
EPDM (Ethylene Propylene Diene Monomer) rubber membrane is another excellent modern flat roofing system. It's particularly popular in the US and is becoming increasingly common in the UK.
Pros of EPDM:
- Lifespan: 25–40 years. Not quite as long as GRP, but far superior to felt.
- Flexible and durable. EPDM is a rubber membrane, so it naturally flexes with thermal movement. This means it's less prone to cracking in cold weather.
- Quick to install. For large, simple flat roofs, EPDM can be faster to install than GRP.
- Cost-effective for larger areas. EPDM tends to be slightly cheaper than GRP per square metre, especially on larger roofs.
Cons of EPDM:
- Seams and joints. Unlike GRP, EPDM sheets have to be joined together. These joints are a potential weak point if not installed properly.
- Appearance. EPDM has a matte black rubber finish, which some homeowners find less attractive than the smooth grey of GRP.
- Requires specialist adhesive. The membrane is bonded to the deck with adhesive, and the quality of the bond depends heavily on the installer's skill and the conditions during installation.
The Comparison at a Glance
| Feature | Felt | GRP Fibreglass | EPDM Rubber |
|---|---|---|---|
| Lifespan | 8–15 years | 30–50 years | 25–40 years |
| Waterproofing | Good initially, degrades | Excellent (seamless) | Very good |
| UV Resistance | Poor | Excellent | Good |
| Maintenance | Regular patching needed | Virtually none | Minimal |
| Appearance | Basic | Smart, smooth finish | Matte black rubber |
| Cost (garage) | £800 – £1,500 | £2,000 – £3,500 | £1,800 – £3,000 |
| Best for | Temporary/budget fix | Most domestic flat roofs | Large flat roof areas |
Our Recommendation
For most homeowners across Staffordshire and Cheshire, GRP fibreglass is the best choice. It offers the longest lifespan, the best waterproofing performance, and requires almost no maintenance. Yes, it costs more upfront — but you won't be paying for another new roof in 10 years.
We install GRP flat roofs across Stafford, Stoke-on-Trent, Newcastle-under-Lyme, Congleton, Stone, and all surrounding areas. Every installation comes with a 20-year manufacturer's guarantee and our own workmanship warranty.
If you're working with a tight budget and need a solution now, felt can work as a short-term fix. But if you're investing in your property for the long term — especially if you're planning to sell — GRP or EPDM are the smart choices.
What About Flat-to-Pitch Conversions?
Some homeowners choose to eliminate the flat roof entirely by converting it to a pitched (sloped) roof. This is especially common for large extensions and garages. A pitched roof sheds water naturally and can last 50+ years with minimal maintenance.
Flat-to-pitch conversions are a bigger job and require building regulations approval, but they can add value to your property and eliminate flat roof problems permanently. Our building division handles these projects regularly — get in touch if you'd like to explore this option.
Get Expert Advice
Not sure which option is right for your property? We're happy to come out, take a look, and give you honest advice — no obligation, no sales pressure. We're rated 10/10 on Checkatrade and trusted by homeowners across the region. Call 01785 305 042 or request a free quote online.
