If you're budgeting for a flat roof on an extension or garage in Dereham, understanding what drives the price up or down will help you spot a realistic quote and avoid nasty surprises.
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Norwich Roofers installs and repairs flat roofs on extensions, garages and commercial buildings in Dereham and across Norfolk. We use EPDM rubber membrane and torch-on felt systems, and provide a full written specification with each price. This page focuses on the cost side of flat roofing: what typical prices look like, what pushes them up, and what it means if a quote seems unusually low.
Flat roofing costs in the UK typically fall in the following ranges for domestic properties, based on current material and labour rates. Prices are per square metre of roof area, supply and fit.
These figures cover the membrane system, perimeter trim, upstand details, and drainage connections on a straightforward roof. They do not include scaffolding, skip hire or structural work. A simple single-garage roof in Dereham of around 15 to 18 square metres might therefore cost anywhere from £800 to £1,800 for felt, or £1,200 to £2,200 for EPDM, depending on deck condition and the level of detail work required.
A larger flat-roofed extension of 30 to 40 square metres with multiple upstand junctions might run from £2,000 to £4,500 depending on the system and deck condition. These are indicative figures, not fixed prices - the only reliable figure comes from a survey of your specific roof.
This is the most straightforward cost driver. Material quantities and the time to lay them scale with area. However, the relationship is not always linear: there are fixed costs in any job - call-out, stripping, waste disposal, setting up - that spread across a larger roof more efficiently than a small one. A 40 square metre roof will not cost twice as much as a 20 square metre roof because some of those fixed costs remain the same.
If you have more than one flat-roofed area that needs attention, having them done at the same time often produces a better overall price than two separate visits.
EPDM costs more to install than felt. The material itself is more expensive per square metre, and the installation process requires careful adhesion work that takes time. The trade-off is a longer serviceable life and fewer maintenance visits over the years. Whether the higher upfront cost is worth it depends partly on how long you plan to stay in the property and partly on your appetite for future maintenance spend.
Torch-on felt is a perfectly sound system for garages and smaller outbuildings where longevity is less critical. For a main house extension where the roof is part of a living space ceiling, most people opt for EPDM when the cost difference is explained clearly.
Deck replacement is one of the bigger variables in a flat roof quote. If the existing boarding is in good condition - solid underfoot, no soft spots, no delamination - it can usually be overboarded or left in place. If the deck has absorbed moisture from a long-standing leak, sections need to come out and be replaced with new exterior-grade plywood.
Replacing 30 per cent of a deck adds meaningfully to the job cost. Replacing the entire deck roughly doubles the material cost. This is why a survey matters: a roofer who quotes without checking the deck is either guessing or planning to charge extras later. A quote that includes a firm deck assessment is worth more than a cheaper quote that does not.
Chipboard decking can swell and delaminate after years of low-level water ingress. Chipboard is far less forgiving of damp than plywood, and once it loses integrity it cannot simply be dried out and reused.
Every junction between the flat roof membrane and a wall or parapet is a detail that takes time and materials. A simple single-storey extension with walls on two sides has two upstand runs. A flat roof surrounded by parapet walls on all four sides has four, plus internal corners. A roof with a roof light, a soil pipe penetration, or an internal drain adds more detail work.
Each additional detail is not hugely expensive in isolation, but they add up. A roof with five penetrations and four upstand runs will cost more to detail correctly than an open roof with one short upstand and a simple gutter edge. When comparing quotes, make sure the specification describes all the detail work explicitly rather than lumping it into a single line item.
Most domestic flat roofs on single-storey extensions and garages can be accessed safely without scaffolding, using a tower or ladder and appropriate edge protection. Some situations do require scaffolding: roofs on two-storey flat-roofed sections, roofs adjacent to a public pavement, or roofs where the working height is sufficient to require a full scaffold system under working-at-height regulations.
Scaffolding for a simple domestic flat roof typically adds £400 to £900 to the job cost depending on the configuration. A roofer who is not asking about access requirements before quoting may be assuming access that turns out not to be available, leading to additional costs when work starts.
Stripping an old felt or membrane roof produces a skip-load of heavy waste. Whether skip hire is included in the quote or added separately is worth confirming before you accept a price. Some roofers include it, others do not. A skip for a domestic flat roof job typically costs £180 to £350 depending on size and location.
A quote that comes in well below others is not always a bargain. Common reasons for a very low price include: specifying a thinner or lower-quality felt grade; proposing to overlay rather than strip the old roof; not allowing for deck replacement; using mastic-only upstand terminations rather than proper termination bars and flashings; or simply underquoting to win the job with extras to follow.
The only reliable way to compare quotes is on a like-for-like written specification. If one roofer is specifying a three-layer torch-on system with full deck replacement and another is specifying a single-layer overlay, they are not quoting the same job and the price difference is not a saving.
A repair on an isolated failure - a split lap joint, a failed upstand section, a cracked flashing - is straightforwardly better value than a full replacement if the rest of the roof is sound. Flat roof repairs for localised problems typically cost £150 to £500 depending on the access required and the extent of the work.
When the roof is over 15 to 20 years old and has multiple failure points, repeated repairs start to cost more cumulatively than a replacement would have. A membrane that is cracking in several places is telling you it is at the end of its life. Patching each crack extends the situation rather than resolving it.
If you have a flat roof on an extension, garage or commercial building in Dereham and you want a realistic price, call Norwich Roofers to arrange a survey. Ask for a survey that assesses the roof properly, confirms the deck condition, and gives you a full written specification and price with no hidden extras.
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