The short answer
The three coverings found on most UK homes are felt, EPDM rubber and GRP fibreglass. Felt is layered bitumen, bonded on in sheets. EPDM is a single synthetic rubber sheet laid in one piece. GRP is a liquid resin laid over glass matting that sets into a rigid shell. Other systems exist, such as asphalt and liquid coatings, but these three cover the majority of extensions, garages and dormers.
Felt: the layered bitumen roof
Felt roofing has been used for generations, and modern versions are far better than the old tarred paper. A built-up system uses two or three layers, a base and one or more cap sheets, each reinforced with polyester and modified with polymers so that the bitumen stays flexible. Most are bonded by melting the underside with a gas torch, which is why the method is called torch-on. Others are self-adhesive or cold-bonded, which suits roofs where a flame is a risk.
Felt is familiar to nearly every roofer, repairs are straightforward, and the typical UK price range for supply and fit is about £60 to £100 per square metre, with a trade view putting modified bitumen at £45 to £75. Its weakness is its seams. Every lap is a place where water can get in if the bond is poor, and the surface of cheap felt cracks and blisters in time. Our guide to torch-on felt roofing goes into the details.
EPDM: the rubber sheet
EPDM is a synthetic rubber, supplied in large sheets, sometimes wide enough to cover a small roof in one piece. It is bonded to the deck with adhesive, or laid loose and held down by ballast. Because there are few or no joints in the field of the roof, there are fewer places to fail. It stays flexible in the cold, tolerates a good deal of movement, and does not need a flame to lay.
The typical UK range reported for supply and fit is around £80 to £120 per square metre, with a trade view giving £70 to £100. The weak points are the details: corners, upstands and penetrations are formed with separate pieces and adhesive or tape, and that is where leaks begin if the work is rushed. The material can be cut by sharp objects, so foot traffic should be limited. See the page on EPDM rubber roofing for more.
GRP: the fibreglass shell
GRP, glass-reinforced plastic, is built on site. Glass matting is laid on the deck and saturated with polyester resin, then finished with a pigmented topcoat. When it sets, it forms a hard, joint-free shell. It is stiff, it takes foot traffic well, and it follows awkward shapes without laps, which makes it a popular choice for small complicated roofs, balconies and dormer tops.
The typical UK range is around £100 to £160 per square metre, with a trade view of £80 to £120. GRP is rigid, so it can crack if the deck beneath moves, and the resin needs dry, mild weather to cure. Our guide to GRP fibreglass roofing sets out the pros and cons in more depth.
Other systems
Beyond the three, there are mastic asphalt, a poured hot bitumen mix used for years on commercial and heritage roofs, and liquid-applied membranes in polyurethane or similar, which are rolled on and cured in place. Metal roofs in lead, zinc or copper are used on bays and special buildings. Single-ply membranes in PVC or TPO are common on larger commercial buildings. You can read about liquid coatings in what liquid roofing is, and commercial roofs have their own section under commercial roofing.
What goes wrong with each
Every covering has a typical way of failing, and knowing it helps you spot trouble. Felt cracks along the ridges of its laps, loses its chippings and blisters where damp is trapped. Rubber is rarely the sheet that fails: the trouble is at the corners, the adhesive at upstands and the places where a sharp object has cut it. Fibreglass crazes or cracks where the deck flexes, and a topcoat that has chalked and worn thin lets the glass show through. In every case, a pool of standing water speeds the damage, and the cause is often the fall, not the covering.
How to choose between them
The right covering depends on the shape of the roof, the state of the deck, what will walk on it, the budget and how long you want it to last. A plain rectangle with sound boards suits rubber well. A small roof with lots of corners and upstands suits fibreglass. A roof where a flame is acceptable and a lower upfront price matters may suit felt. Comparisons by price alone miss the details, which is why our page on EPDM, GRP and felt compared weighs them against each other.
The figures above are typical UK ranges reported by third-party cost guides, figures from outside sources, not a price list of ours. Your fixed quote follows the survey, which is free and includes photographs of your own roof, and we explain which of the three we think suits it, and why. If a repair is enough, we say so. For the full set of systems we fit, see flat roofing in Basingstoke.
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