The short answer
Felt, particularly modified bitumen, is generally the lowest-priced covering. Typical UK ranges reported by cost guides are £60 to £100 per square metre for felt, £80 to £120 for EPDM and £100 to £160 for GRP, supplied and fitted. Trade sources put modified bitumen lower still, at £45 to £75. These are figures from outside sources, not a price list of ours. Your fixed quote follows the survey. A low rate buys less if the deck needs work.
The per-metre rates
Published UK cost guides give a spread for each covering. Felt comes lowest at about £60 to £100 per square metre, EPDM rubber at £80 to £120, and GRP fibreglass at £100 to £160, all supply and fit. A contractor-facing guide gives EPDM at £70 to £100, GRP at £80 to £120 and modified bitumen at £45 to £75. The two sets differ because they come from different sources and sample different jobs.
Treat them as typical ranges reported by third parties, not as a price list. A small roof costs more per metre than a large one, because set-up, access and detailing do not shrink with the area. Our page on how much a flat roof costs goes through the factors in detail, and the main costs guide covers the wider picture.
What the cheap quote leaves out
The membrane is only part of a roof. Stripping the old covering, repairing or replacing a rotten deck, adding insulation, new trims and outlets, scaffolding and waste disposal all add to the bill. A rate that quotes the covering alone can double once the real condition of the roof is known. A cheap quote that assumes the existing boards are fine, and then adds a charge once the roof is open, is not cheap.
Insulation is another gap. When a flat roof covering is replaced, the roof is a thermal element and generally has to meet current standards under Approved Document L, which means insulation. A quote that leaves it out may be cheaper on paper but may not satisfy building control. We handle that side where work is notifiable.
Cheapest now or cheapest over time
A low-cost covering that wears out in half the time costs more over the years. Standard felt, laid thin on a busy roof, can start cracking and blistering early. A properly laid rubber or fibreglass roof may last considerably longer for a higher outlay. Our page on how long a flat roof lasts compares them, and our guide to EPDM, GRP and felt sets out the other differences.
The cost of a leak is also real. A small leak in a bedroom ceiling brings plasterwork, redecoration and sometimes timber replacement, none of which a saving on the membrane will cover. The sensible comparison is the total cost per year of use, with the repair risk in view.
Ways to spend less without cutting corners
Some savings are real. Keeping a sound deck instead of replacing it saves money, as does overlaying where the existing roof is dry and flat, which we discuss in laying a new flat roof over the old one. A repair, where it is the honest answer, is far cheaper than a replacement. A simple roof shape with few penetrations is cheaper to cover than a complicated one.
Other savings are false. Skipping insulation, using thin boards, leaving out edge trims or using the wrong adhesive will cost less today and more soon. If you see a quote far below the others, ask what it excludes.
Small roofs and big roofs
Per-metre rates are least reliable at the extremes. A porch roof of a few square metres costs far more per metre than a large extension, because scaffolding or access, materials delivery, trims, outlets and the crew's time do not shrink with the area. Many roofers have a minimum charge for that reason. At the other end, a large plain roof earns a keener rate because the laying is quick once the crew is set up. If you are comparing a quote for a tiny roof with a published per-metre figure, expect the quote to look high, and ask what is in it.
Cheaper options that are sometimes right
On a shed, a lean-to or a small garage that will not be walked on or seen from the house, a basic felt or a lighter roofing sheet may be all that is wanted. The honest answer to a question about the cheapest roof is sometimes that a plain, thin covering is fine for a building that does not matter much. Our guide to garage roof materials covers those lighter options.
How we price
We look at the roof before we put a number on it. The survey is free and includes photographs of your deck and covering, so you can see what drives the figure. We say whether a repair would do, and if a replacement is the sensible option we compare the materials honestly, including felt where it makes sense. The written quote is fixed, and ten years of written workmanship cover stand behind the finished roof. Further detail on our systems is under flat roofing in Basingstoke.
Every roof is different. A free survey with photos settles it for yours.
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