Merton at a glance
- Postcode districts
- SM4, SW20, SW19, CR4
- Council area
- London Borough of Merton
- Building approval
- London Borough of Merton building control, or a registered building control approver
- Guide price region
- London (+20% on West Midlands rates)
What does a dormer roof in Merton need?
High, exposed dormers in Merton take the full force of the wind and rain. Edge trims loosen, flashings lift and the felt at the drip edge cracks. Once the faults spread around the perimeter, a new roof with fresh trims usually lasts far longer than another round of repairs.
Merton's flat roofs are mostly on kitchen extensions and roof terraces behind period houses, with plenty on shops with flat-roofed stores below flats above too. The Thames basin is one of the drier parts of Britain at roughly 730 mm of rain a year, but summer heat is the bigger test here: dark membranes on south-facing roofs swing a long way in temperature.
How much does a new dormer roof cost in Merton?
At London guide rates, an 8 m² GRP dormer roof including scaffold comes to £1,700–£3,200 including VAT. The fixed price comes after a free survey for new and replacement roofs.
| Job | Guide price inc VAT |
|---|---|
| Dormer (8 m²), GRP, scaffold | £1,700–£3,200 |
| Single garage (18 m²), EPDM rubber | £1,900–£3,350 |
| Extension (20 m²), GRP, new deck + insulation | £3,600–£6,450 |
Why is scaffold and tile detailing so important on a dormer?
Because a dormer roof is high, small and surrounded by a pitched tiled roof, most failures happen at the edges rather than in the middle. Safe access is what allows those edges to be done properly.
Ladders alone do not give a safe working platform at that height, and every roof is treated as fragile until a competent person confirms otherwise. Scaffold with edge protection lets the team work along the front and sides of the dormer, and reach the junction with the main roof.
The back of the dormer is where most leaks start. The new membrane has to turn up under the tiles or slates, with a flashing that sheds water over it. Where the old detail used lead, we reinstate or replace it. Small roofs also leave little room for error at the drip edge: the front trim must throw water clear of the window frame and fascia, and any gutter has to be big enough for the area it drains. Dormer cheeks with tile hanging or cladding are checked for gaps that let water behind.
If you are also planning insulation upgrades or work on the main roof, tell us at survey so the scaffold can be shared.
What's included?
- Strip-out of the old covering and deck repairs
- Written workmanship guarantee, with building control handled where needed
- Free survey of the dormer roof, cheeks and main roof junction
- Scaffold with edge protection, priced in the quote
Building regulations in England
Replacing more than half of a flat roof over a heated room usually counts as renovating a thermal element, so the roof is insulated to around 0.16 W/m²K where that's technically and economically feasible, and the work is notified to building control: the council or a registered building control approver, unless a registered competent person self-certifies it. A roof on a new extension is built to 0.15 W/m²K. Patch repairs, and most unheated detached garages, don't trigger the upgrade. Structural changes, or a new covering that adds 15% or more to the roof's weight, also need approval. More on the rules.
Which nearby areas do we also cover?
- Sutton · 3 mi
- Wandsworth · 4 mi
- Kingston upon Thames · 5 mi
- Croydon · 5 mi
- Lambeth · 5 mi
- Richmond upon Thames · 6 mi
Dormer roofs in Merton: questions
Do you cover Merton?
Yes. Merton is part of our London coverage, including postcode districts SM4, SW20, SW19, CR4. Surveys and roofs are carried out by vetted roofing teams working under S&K Property Investments and Improvement Ltd.
Who checks building regulations for a flat roof in Merton?
Where the work needs approval it goes to London Borough of Merton building control, or a registered building control approver. We tell you at the survey whether your job needs it and deal with the paperwork as part of the quote.
How much does a new dormer roof cost in Merton?
£1,700–£3,200 for an 8 m² GRP dormer roof including scaffold, at London guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Does the room below need emptying?
No, but moving furniture away from the window and covering the floor is sensible. The room stays usable throughout.
Will insulating my dormer roof make it higher?
Yes, by the insulation thickness. We plan the build-up so the new roof still sits correctly under the main roof tiles at the back edge.