Westminster at a glance
- Postcode districts
- W1K, W1C, W1H, W1U, W1M, W1G, W1, W1J and 20 more
- Council area
- City of Westminster
- Building approval
- City of Westminster building control, or a registered building control approver
- Guide price region
- London (+20% on West Midlands rates)
What does a dormer roof in Westminster need?
If your dormer in Westminster was added years ago with a basic felt roof and little insulation, it will tend to fail at the edges first, and they leave the loft room cold in winter and hot in summer. A warm-roof replacement deals with both problems at once.
In and around Westminster, flat roofs are typically found on kitchen extensions and roof terraces behind period houses, and on mansion blocks and purpose-built flats with large flat roofs. 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 Westminster?
Guide price in Westminster: £1,700–£3,200 for an 8 m² GRP dormer roof including scaffold, including VAT at London rates. 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 |
Is GRP or EPDM better on a dormer roof?
GRP fibreglass is often the first choice on a dormer, because it is laid as a liquid resin over a mat and forms neat, rigid edges, corners and drip details on a small roof. It cures to a hard surface that copes with occasional foot traffic during window cleaning or maintenance.
EPDM rubber works well on a plain rectangular dormer and can usually be laid as one sheet, with no field joins. Unlike GRP, it does not depend on resin curing conditions on the day. Torch-on felt can be used, but working a torch close to timber cladding, fascias and tiles needs extra care, so a cold-applied system is often chosen instead.
We recommend the system after surveying the dormer, its edges and how it meets the main roof.
What's included?
- Warm-roof insulation and a vapour control layer
- Scaffold with edge protection, priced in the quote
- Strip-out of the old covering and deck repairs
- New membrane, drip trims and back-edge abutment under the tiles
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?
- Camden · 1 mi
- Kensington and Chelsea · 2 mi
- Islington · 3 mi
- Hammersmith and Fulham · 3 mi
- Lambeth · 4 mi
- Southwark · 4 mi
Dormer roofs in Westminster: questions
Do you cover Westminster?
Yes. Westminster is part of our London coverage, including postcode districts W1K, W1C, W1H, W1U, W1M, W1G and 22 more. 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 Westminster?
Where the work needs approval it goes to City of Westminster 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 Westminster?
£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.
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.
Is a dormer roof cheaper than a garage roof?
Not by as much as the size suggests. Scaffold and the extra detailing at height mean a small dormer roof often costs about the same as a single garage roof.