Flat Roof Materials: Felt, EPDM, GRP and Single Ply Compared

Choosing a flat roof covering is one of the biggest decisions on an extension, garage or porch. The material you pick decides how long the roof lasts, how well it copes with movement and weather, and how much it costs now and in the future. There are four main options in the UK: felt, EPDM rubber, GRP fibreglass and single ply membrane.

This guide compares them side by side, so you can see which flat roof material suits your roof and budget. For the wider picture, including insulation and costs, see our flat roof guide.

Flat Roof Materials at a Glance

These figures are guides. A well-fitted roof in a cheaper material will outlast a badly fitted roof in a better one, so the installer matters as much as the product.

Felt Flat Roofs

Felt is the traditional flat roof covering. Modern felt roofs use modified bitumen sheets, normally laid in two or three layers and bonded with heat. They are cheap, familiar to most roofers and easy to repair in small sections.

• Pros: low cost, quick to fit, easy to patch, suits awkward shapes.
• Cons: shorter life than other options, relies on well-bonded laps, and torch-on work carries a fire risk.

For more on how it is installed and what to ask your roofer, read our guide to torch on felt roofs.

EPDM Rubber Flat Roofs

EPDM is a synthetic rubber membrane, usually supplied in a single large sheet that is glued to the roof deck. Because a small roof can be covered in one piece, there are few or no joins for water to find.

• Pros: long life, flexible in cold and hot weather, resistant to UV and ponding, and few seams.
• Cons: can be punctured by sharp objects or careless foot traffic, and it needs a clean, dry deck and careful edge details.

EPDM is now the most popular choice for domestic flat roofs because of its long life and low maintenance. A properly fitted EPDM roof is often a good all-round option for a standard extension.

GRP Fibreglass Flat Roofs

GRP stands for glass reinforced plastic. A roofer lays fibreglass matting on the deck, saturates it with resin and finishes it with a coloured topcoat, creating a hard, seamless surface.

• Pros: seamless, strong, walkable and very watertight on small roofs. It can be finished in a range of colours.
• Cons: it is rigid, so it needs a stable deck, and movement in the building can cause cracks. Quality depends heavily on the weather conditions on the day and the skill of the installer.

GRP is a favourite for small roofs, dormers, balconies and porches, where its seamless finish is a real advantage.

Single Ply Membrane Roofing

Single ply roofing uses a factory-made sheet of PVC or TPO, laid in one layer over the insulation. The sheets are joined by hot-air welding, which fuses the edges together, and the membrane is held down by mechanical fixings, adhesive or ballast.

• Pros: strong welded seams, good UV and weather resistance, lightweight and quick to install over large areas. Many products are available in light colours that reflect heat.
• Cons: it is more common on commercial buildings, fewer domestic roofers fit it, and it needs trained installers to weld seams correctly.

EPDM is technically also a single ply membrane, but it is usually treated as its own category on homes because of the way it is fitted.

Other Flat Roof Coverings

• Liquid-applied membranes: a liquid coating applied by roller or spray. These are often used to restore an older roof and can extend its life without a full strip-out.
• Lead and zinc: metal coverings used on traditional buildings and some modern designs. They are expensive but very long-lasting. See our metal roof guide for the main options.
• Green or sedum roofs: a layer of plants grown over a waterproof membrane. They are heavy, need extra structural support and cost more, but they offer good insulation and a natural look.

Which Flat Roof Material Is Best?

There is no single best material, but these rules of thumb help:

• Tight budget: felt in at least two layers.
• Standard house extension or garage: EPDM, for its long life and few seams.
• Small, complicated or walkable roof: GRP.
• Large, open roof or a commercial building: single ply PVC or TPO.
• Old roof that is still sound: a liquid-applied coating may be enough.

The material is only one part of the roof. The deck, the fall, the insulation and the edge details all affect how long it lasts. Our guide to warm roof construction explains how the layers beneath the covering should be built.

Common Flat Roof Repairs

• Felt: blisters, splits and lifted laps are patched with matching felt, or the whole section is re-covered.
• EPDM: small punctures are repaired with patches and adhesive tape, while large tears may need a new sheet.
• GRP: cracks are sanded back, re-laminated and finished with a new topcoat.
• Single ply: damaged sections are cut out and a welded patch is fitted.

Water on a flat roof often travels before it shows inside, so finding the real source is half the job. Our guide on how to fix a leaking roof shows how to trace it.

Questions to Ask Before You Choose

• Which exact product will be used, and what is its guarantee?
• Is the roof being built as a warm roof, and how thick is the insulation?
• How will the fall, edges and outlets be finished?
• Who will install it, and are they trained in this specific system?
• What does the guarantee cover, and does it include the labour?

Compare at least three written quotes on the full specification, not only on price. Our guide to reading a roofing quote shows what to look for.

Frequently Asked Questions

What is the best flat roof material?

For most homes, EPDM is the best all-round choice because of its long life and few seams. GRP suits small roofs, and felt is the budget option.

What is single ply roofing?

Single ply roofing is a factory-made membrane, usually PVC or TPO, laid in one layer. The sheets are joined by hot-air welding and the roof is normally fixed with mechanical fixings, adhesive or ballast.

Which flat roof material lasts longest?

EPDM is often quoted at 30 to 50 years, which is longer than felt, GRP or single ply, though installation quality has a big effect on every material.

Is GRP better than EPDM?

Neither is better in every case. GRP is seamless and very strong underfoot on small roofs, while EPDM is flexible and better suited to larger roofs and buildings that move.

Can I put a new flat roof over an old one?

Sometimes, but it is usually better to strip the old covering so that the deck can be inspected. Covering a wet or damaged deck hides problems that will show up later.

Do all flat roofs need insulation?

New and replacement flat roofs usually need to meet current building regulations, which means adding insulation. A warm roof build-up is the most common solution.

Final Thoughts

The best flat roof material depends on the size, shape and use of the roof, as well as your budget. Felt, EPDM, GRP and single ply can all give you a long-lasting roof when they are installed properly. Pay close attention to the build-up, the edges and the guarantee, and compare detailed quotes before you commit.