The short answer
A dormer is priced job by job, not by the window. A small rebuild of an existing dormer roof and cheeks costs a fraction of a new structural dormer, and what moves the figure is the size, the covering, the lead, the scaffold and the structure underneath. We do not quote a dormer from a price list, so we look at the roof before naming a figure.
Why a dormer has no standard price
A dormer is a small structure that stands up out of a sloping roof so that a window can sit upright and a loft room gains headroom. It has a roof of its own, two side walls called cheeks, a face that carries the window, and a set of junctions where all of that meets the main roof. Each of those is a separate task with its own materials.
Two dormers that match from the pavement can cost very different amounts. One may have a flat roof covered in a single-ply membrane, the other a pitched roof in slate with lead at every edge. One may have timber cheeks hung with tile, the other stone or render. The window in the face is often the smallest part of the bill. Our roof windows and skylights hub covers the glazing side of the work.
For that reason cost guides tend to price roof windows, flat roofs and slate roofs separately, and a dormer borrows from all three. Be wary of any figure that arrives without anyone having looked at the roof it is meant for. A phone estimate for a dormer can only ever be a guess, and the guess usually misses the lead, the access and the rot that hides behind the cladding.
What moves the price
These are the things that decide where a dormer job lands.
- New build or rebuild. Adding a dormer where none exists means opening the roof, framing the structure and often altering the floor and stair inside. Rebuilding a tired dormer keeps the structure and renews its skin.
- Size and number. A wide dormer takes more roof, more cheek and more lead than a narrow one, and a pair is not simply double.
- The covering. A dormer roof in natural slate, clay, lead or a flat membrane each carries a different material and labour cost, and old roofs often call for matching the main slope.
- The leadwork. Lead cheek flashings, back gutters and soakers are skilled work and a significant share of the total. Lead is sold in codes by thickness, and Royston Lead's brochure lists every code from 4 (1.80 mm) up to 8 (3.55 mm) as suitable for dormers, so the code is chosen to suit the detail.
- Access. Scaffold may be required. MyBuilder's 2026 new roof guide puts scaffolding at about £1,125 for a whole-roof job, which gives a sense of scale rather than a figure for yours.
- Condition underneath. Rotten rafters, wet insulation or a failed cheek frame only show once the covering is off.
Cost guides you can use as context
Published guides do not give a headline figure for dormers, so we will not invent one. They do give ranges for the parts a dormer is made of, and these are typical UK figures from MyBuilder in 2026, not Empire prices.
| Part of the work | Typical UK range |
|---|---|
| Roof window installation, labour and fitting | £350 to £600, window extra |
| Roofing labour on a pitched roof | £50 to £130 per m² |
| Slate roof, installed | £100 to £180 per m² |
| Lead flat roof, installed | £150 to £200+ per m² |
| Scaffold, roof-wide job | about £1,125 |
Use those as a way to check a quote is plausible, not to build your own total. A dormer is small, so the area figures apply to a handful of square metres, and the fixed costs of access, setting out and leadwork weigh heavily on the final sum.
Rebuilding versus adding
Many enquiries are for work on a dormer that already exists, where the roof has failed or the cheeks have begun to leak. Because the structure is standing, that is a repair-and-renew job, and the first question is whether repair works. A split lead flashing or a few slipped slates on the cheek can be mended. A dormer whose cheek timbers have rotted behind the cladding needs rebuilding, and it is better to know that before the price is agreed. Our page on why a dormer leaks lists the usual weak points.
Adding a new dormer is a larger undertaking. It involves structural design, Building Regulations approval for the alteration, and possibly planning. It is worth reading whether dormers need planning permission before you spend anything on drawings.
In Bath, consent can add steps and cost. If the house is listed, a dormer is a matter for B&NES listed building consent, and our page on the listed building dormer explains what to expect.
How we price a dormer
We start with a free survey of your roof, with photographs of what we find on your own dormer or on the slope where you want one. That shows the covering, the state of the cheeks, how the lead was dressed, and whether scaffold is needed. A fixed price in writing follows, so the figure you agree is the figure you pay.
We favour repair where repair works, and where a dormer has to be rebuilt we match the materials to the main roof, so a natural slate house gets a slate dormer. The site is cleared and waste taken away at the end, and a written 10-year workmanship guarantee goes with the job.
One related point is insurance. If a dormer has been damaged by a storm, your cover may respond, and our note on roof window insurance sets out how storm damage and wear are treated. To get a figure for your own dormer, ring 01225 285181 or send photographs through WhatsApp or the form.
