If your flat roof needs replacing, one of the first decisions you will face is which material to use. Twenty years ago the answer was almost always felt. Today there are better options available that last longer, perform better and often work out cheaper over time because they do not need replacing every decade.
Here is an honest comparison of the three main flat roof materials we install across Bedfordshire, with the pros and cons of each.
GRP fibreglass
GRP (glass reinforced plastic) has become the go-to choice for most domestic flat roofs, and for good reason. It is laid as a liquid resin over a glass fibre mat, which cures to form a completely seamless, rigid, waterproof surface. There are no joints, no seams and no overlaps for water to find its way through.
Pros:
- Completely seamless finish with no weak points
- Lifespan of 25 to 30 years or more when correctly installed
- Does not crack, blister or delaminate like felt
- Extremely low maintenance, just keep it clear of debris
- Can be walked on for occasional access
- Available in a range of finishes and colours
Cons:
- Higher upfront cost than felt
- Must be installed in dry conditions as the resin will not cure properly in rain or very cold temperatures
- Requires a skilled installer, a poor GRP installation will crack and fail
GRP is what we recommend for most garage roofs, extension roofs, bay window roofs and dormer roofs across Bedford, Luton, Dunstable and the surrounding area. The higher upfront cost is offset by the much longer lifespan and the fact that you will not be paying for another replacement in ten years.
EPDM rubber
EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane that comes in large sheets. It is bonded to the roof deck with adhesive, creating a flexible, watertight covering. EPDM has been widely used in commercial roofing for decades and is increasingly popular for domestic applications as well.
Pros:
- Very long lifespan, 30 to 50 years in many cases
- Flexible, so it handles building movement and temperature changes without cracking
- Can be installed in a wider range of weather conditions than GRP
- Excellent for large flat roof areas where a seamless GRP application would be impractical
- Low maintenance
Cons:
- Seams and joints are needed on larger roofs, and these are potential weak points if not bonded correctly
- The surface can be punctured by sharp objects or heavy foot traffic
- Aesthetically it looks like what it is, a rubber sheet, which some homeowners find less appealing than a GRP finish
Torch-on felt
Torch-on felt is the modern version of traditional roofing felt. It is applied in layers using a gas torch to melt the bitumen backing and bond it to the roof. It is a significant improvement on the old cold-applied felt systems, but it still has limitations compared to GRP and EPDM.
Pros:
- Lower upfront cost than GRP or EPDM
- Established technology that most roofers are familiar with
- Suitable for some applications where budget is the primary concern
Cons:
- Shorter lifespan, typically 10 to 15 years before it needs replacing
- Seams and overlaps are vulnerable to splitting and water ingress over time
- Can blister and crack in hot weather
- Requires more regular maintenance and inspection
- The long-term cost is often higher than GRP because you will replace it more frequently
So which should you choose?
For most homeowners in Bedfordshire, we recommend GRP fibreglass. It is the best balance of durability, performance and long-term value. EPDM is an excellent choice for larger commercial or domestic flat roofs where the area is too big for a practical GRP application. Felt still has its place for budget-sensitive projects, but we always make sure customers understand they will be replacing it again in 10 to 15 years.
The best way to decide is to get a professional to look at your specific roof, assess the deck condition, the drainage, the access requirements, and recommend the right material for your situation.
We offer free flat roof surveys across Bedford, Luton, Dunstable, Leighton Buzzard and the wider Bedfordshire area. Call 07951 017 425 or email info@dextersbuild.co.uk for honest advice and a no-obligation quote.
