What Is the Best Flat Roof Material? Felt, Fibreglass and EPDM Compared

If you have a flat roof on an extension, garage, dormer or bay, sooner or later you will face this decision. There are three materials that dominate the UK domestic market and they are not equal. Here is the honest comparison.

Felt: The Old Default

Torch on felt has covered British flat roofs for generations. It is the cheapest option upfront and a competent felt roof will give you roughly ten to fifteen years. Its weaknesses are the joints and the material itself. Felt is laid in overlapping strips, every overlap is a potential failure point, and the material goes brittle with age and ultraviolet exposure, then cracks and blisters.

The other problem with felt is cultural rather than technical. Because it is cheap, failed felt roofs tend to get refelted over the top rather than stripped, and many British flat roofs are now three or four layers deep, each layer trapping moisture beneath it. If your flat roof has been patched more than once, the next intervention should almost certainly not be more felt.

GRP Fibreglass: Seamless and Hard Wearing

GRP is a fibreglass laminate laid wet onto boarding and cured into a single seamless skin with no joints anywhere. No joints means no joint failures, which removes felt's biggest weakness at a stroke. Properly installed GRP carries life expectancies of twenty five to thirty years or more, resists foot traffic well and gives a clean finish that suits roofs you can see from upstairs windows or use as balconies.

Its requirements are dry installation conditions and good boarding underneath, which is why preparation is most of a GRP job. It costs more than felt upfront and considerably less than felt over its lifetime.

EPDM Rubber: Flexible and Long Lived

EPDM is a synthetic rubber membrane supplied in sheets large enough to cover most domestic roofs in a single piece, again eliminating joints. It stays flexible in cold weather rather than going brittle, shrugs off ultraviolet light and carries credible life expectancies of thirty to fifty years. It is quick to install, handles building movement well and is the forgiving choice on garage roofs and larger simple rectangles.

Aesthetically it is a matt black rubber finish, which some prefer less than GRP on prominent roofs, and detailing around complex shapes is less elegant than GRP's moulded edges.

So Which Is Best?

For most extensions, dormers and visible roofs, GRP fibreglass is the strongest all rounder. For garages and large simple roofs where speed and flexibility matter, EPDM is excellent. Felt still has a place on short term and budget jobs, but as a long term covering it is the weakest of the three, and replacing felt with felt is usually a decision you make twice.

If you are unsure which your roof needs, we will inspect it, tell you honestly whether repair or replacement is the right call and quote both where both are viable. Free quotes, no deposit, call 0800 474 8347.