Cambridge Roofers installs and repairs flat roofs in Great Shelford, and this page sets out what jobs typically cost, what drives the price up or down, and how to make sure you are comparing quotes fairly.
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Flat roofing is one of the services where prices vary most widely between quotes - and often for good reason. Two quotes for the same roof can differ by 50 per cent or more without either contractor being dishonest. The difference is almost always in what is included, what system is specified, and what assumptions are being made about the condition of the existing deck. This page breaks down the main cost components for flat roofs in Great Shelford so you can compare quotes properly and make an informed decision.
A full strip and re-cover on a domestic flat roof in Great Shelford and the surrounding area typically costs between £70 and £120 per square metre, all in. That range covers stripping the old surface, inspecting and carrying out minor repairs to the deck, laying insulation, installing the new membrane system, and fitting new drip edges, outlets, and flashings.
In practical terms, that translates to:
These are working estimates for typical domestic work. The actual price for your roof will depend on the factors below.
The membrane system is the first factor that splits quotes apart. EPDM rubber membrane costs more in materials than torch-on modified bitumen felt, and the price difference shows in the overall quote. A 30-square-metre extension roof might cost £2,800 to £3,500 in EPDM and £2,000 to £2,800 in torch-on felt, depending on specification.
EPDM has a longer expected service life - typically 25 years or more when correctly installed - compared with 15 to 20 years for a well-installed two-layer torch-on felt system. Over the life of a property, the higher upfront cost of EPDM usually represents better value, particularly on a roof that will not be easy or cheap to access for the next re-cover. If you are planning to sell in the next few years and the roof otherwise just needs a refresh, torch-on felt is a legitimate and honest choice. If you plan to stay in the property, EPDM is worth the additional cost.
The deck - the structural surface the membrane sits on - is the biggest source of unexpected cost in any flat roofing job. On a roof that has been leaking, the timber below is almost always wetter and softer than it appears from the surface. Once the old membrane is stripped, soft, rotted, or deflecting sections need to be cut out and replaced with new plywood or OSB board before the new membrane can go down.
Deck replacement is priced by the sheet or the square metre, and the cost can add anywhere from a few hundred pounds to over a thousand on a roof that has been leaking for more than one or two seasons. A roofer who surveys the job thoroughly before quoting can give you a clearer picture of this risk, but it can never be fully quantified until the old surface is off. Ask any contractor how they handle deck repairs found during the job - whether those costs are agreed in advance as a rate per sheet, or whether they are treated as open-ended extras.
A flat roof must shed water. Building regulations require a minimum fall of 1 in 80 - roughly 12mm drop for every metre of run. Many older flat roofs, particularly on extensions built before the 1990s, were never given adequate falls, and the standing water that results is the main cause of early membrane failure.
Correcting inadequate falls during a re-cover is done using tapered insulation boards, which build up the slope across the roof surface. This adds to both the material and labour cost, but it is a one-off investment that extends the life of the new membrane significantly. A roof relaid with the same inadequate falls will fail for the same reason as the old one, regardless of how good the new membrane is. If a quote does not mention falls or drainage, ask specifically what fall is being built in.
The depth and quality of insulation in the roof build-up affects both cost and long-term performance. Current building regulations set minimum U-values for new and replacement flat roofs. Meeting those values requires at least 100mm of high-performance rigid insulation board in a warm roof build-up, which adds cost compared with a thinner or lower-grade product.
Quotes that show a lower price per square metre often include thinner or cheaper insulation. This is not always obvious from the description. Ask for the insulation specification - product, thickness, and the resulting U-value - when comparing quotes. A quote that includes proper insulation and one that does not are not equivalent, even if both describe themselves as a full re-cover.
Most single-storey flat roofs can be accessed safely with steps or a short scaffold tower. If the roof is over a two-storey extension or is otherwise difficult to reach, a scaffold structure may be required, adding £300 to £800 or more depending on the complexity of the access. This is a genuine cost that not all contractors include in their initial quote, so confirm whether access equipment is included in the price before signing anything.
Access requirements also affect how long the job takes. A straightforward single-storey garage roof can be completed in one to two days. A larger or more complex roof might take three to four days, which in turn affects the labour cost.
Any flat roof re-cover is an opportunity to replace aging drainage outlets and rooflights, and the cost of doing so at the same time as the re-cover is significantly lower than returning to do it separately. A new low-profile drainage outlet costs £30 to £80 in materials. A flat rooflight in a standard size costs from around £200 to over £800 depending on the specification. Adding these at re-cover time means the membrane can be properly detailed around them from new, rather than cut and patched later.
Ask your roofer to assess outlets and rooflights as part of the survey and include any replacements in the quote if they are approaching the end of their useful life.
A repair is the right choice when the membrane is still structurally sound, the deck is dry and undamaged, the falls are adequate, and the failure is genuinely localised - a split at an upstand, a failed outlet seal, or a puncture. In those circumstances, a targeted repair costing £150 to £500 can add several years to a roof's life.
A full re-cover is the right choice when the membrane is more than 15 to 20 years old, when ponding water has been present, when the deck is soft in multiple areas, or when repeated repairs have failed. Patching a roof that is past its serviceable life rarely holds for more than one or two winters and typically costs more in total than a single re-cover would have.
To compare quotes properly, make sure each one specifies the same things: the system being installed, whether the existing surface is stripped, how deck repairs are priced, what fall is being achieved, the insulation specification, and what edge and flashing details are included. A quote that is vague on any of those points is likely to generate extras during the job.
We work on flat roofs in Great Shelford and across the nearby Cambridge area. If you would like a survey and a detailed quote that covers all of the above, call us and we will arrange a time to inspect the roof properly before any figures are discussed.
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