It's the first thing everyone wants to know, and the hardest to answer in one number: what will a new flat roof actually cost? The honest answer is that it depends on the size, the material, the state of what's underneath and how easy the roof is to get to. But "it depends" is no use when you're trying to budget, so below are the real ballpark figures for the UK in 2026, what's usually included, and the things that move the price.
The short answer
Flat roofs are usually priced per square metre (m²) of roof area, then adjusted for access and the condition of the deck. As a rough guide for a typical domestic roof:
| System | Typical price per m²* | Expected lifespan |
|---|---|---|
| Felt (torch-on) | £40 - £80 | 10 - 15 years |
| EPDM rubber | £80 - £110 | ~20 years |
| GRP fibreglass | £90 - £130 | 30 - 40 years |
*These are general UK market ranges to help you budget, not a quote. Your actual price depends on your specific roof, and the only accurate figure comes from a site visit.
In whole-job terms, that usually works out as:
- Small roof (porch, bay, small garage, under 10m²): often around £1,200 - £2,000, as small jobs still take a full day and a minimum of materials.
- Typical extension or garage roof (15 - 25m²): roughly £2,000 - £3,500 for a quality GRP finish.
- Larger or more complex roof (30m² and up): £4,000 and upwards, depending on detailing and access.
What's included in a proper quote
A fair fixed-price quote should cover more than just the waterproofing layer. For a new GRP roof, you'd normally expect it to include:
- Stripping off the old covering and clearing it away.
- A new 18mm OSB3 timber deck if the existing one is tired or uneven.
- All the trims, drip edges and upstands.
- The full fibreglass build-up and coloured topcoat.
- Labour, waste disposal and, where needed, scaffolding or access equipment.
If a quote looks unusually cheap, it's worth checking what has been left out, the deck and the trims are common places for corners to be cut.
What pushes the price up or down
Two roofs of the same size can be priced quite differently. The main factors:
- Access. A ground-floor garage is quick. A second-storey roof that needs scaffolding costs more before a single tile is touched.
- The deck underneath. If the timber below is rotten or sagging, it needs replacing, which adds materials and labour. A sound deck keeps the price down.
- Complexity. Rooflights, pipes, vents, changes of level and lots of edges all take time to detail properly.
- Tear-off vs overlay. If your existing roof is structurally sound, a GRP overlay can sometimes go straight over the top, saving the cost and mess of a full strip-out.
- Finish. Standard colours cost less than bespoke ones, and a non-slip walk-on finish is a little more than a smooth one.
Repair or replace?
You don't always need a whole new roof. If your covering is only a few years old with one isolated leak, a repair may be all that's needed, and it will cost a fraction of a replacement. It's when a roof has been patched more than once, or you're chasing the same leak every winter, that a replacement starts to make financial sense. We cover that decision in more detail in flat roof repair or replace?, and if you're not sure which camp you're in, the signs a flat roof needs replacing is a good place to start.
Getting an accurate number
Every figure above is a guide. The only way to know what your roof will cost is to have someone measure it, check the deck and look at the access. We do that for free, and you get a written, itemised, fixed price with no day-rate creep and no surprises, so the number we quote is the number you pay. If you'd like to compare systems first, our guide to GRP vs felt vs EPDM lays out the trade-offs.
Free, fixed-price quote, no pressure. Call 07976 730433 or request one here.
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