Cost Guide
Dormer Attic Conversion Cost
What a rear or side dormer conversion costs in 2026, what drives the price, and what a headline quote leaves out.
Honest Pricing
Why a dormer costs more than a rooflight
A dormer conversion costs more than a Velux or rooflight conversion because it does more. Instead of leaving your roof shape as it is, a dormer opens up the roof and builds outwards, adding real structure and usable head height where a rooflight room would be too tight. That extra work is exactly what you are paying for, and it is also why a price cannot be given honestly over the phone.
- ✓ Adds real structure and usable head height
- ✓ A written breakdown, not a headline figure
- ✓ Indicative ranges confirmed at a free site survey
The ranges on this page are indicative, not quotes. We would rather be straight with you than win the job with a low number that falls apart on site. For the full picture across every conversion type, see the full cost guide.
Indicative Cost
What a dormer conversion typically costs
Indicative range only, not a quote. Final cost depends on dormer size, finish, roof type and access. Figures to be confirmed with the client before launch.
A dormer sits above a rooflight conversion because it adds structure and head height. A dormer with an en-suite costs more again, since the plumbing, drainage and ventilation add to the base build; see our en-suite conversion cost guide for that side of it.
The Line Items
What moves the price
A dormer price is the sum of real, separate pieces of work. When you understand the parts, you can see why two quotes differ and where a cheap one has cut a corner. The euro figures are confirmed after an on-site assessment of your home.
- ✓Dormer sizeA larger dormer means more structure, roofing, cladding and internal finish, so the floor area and head height gained are the biggest single driver.
- ✓Rear versus sideA rear dormer is often more straightforward than a side dormer, which can involve the gable, party lines and different access.
- ✓Roof structure (cut versus truss)A traditional cut roof is usually easier to open up than a modern trussed roof, which needs more structural support to replace what is removed.
- ✓The staircaseA compliant, fixed staircase is a building-regulation requirement, and fitting one while keeping headroom below often shapes the whole layout.
- ✓PlanningWhether the dormer needs permission depends on size, position and your property, which affects both timeline and cost.
- ✓Finish levelStandard versus high-end joinery, flooring, tiling and fittings can move the final figure significantly, which is why like-for-like comparison matters.
Is It Worth It
Is a dormer worth the extra over a Velux?
It depends on your roof. Where head height is already good, a rooflight conversion is usually the better value because it leaves the roof largely in place. Where head height is tight, a dormer is often the only way to get a room that meets habitable standards, and in that case the extra cost is buying you usable space you could not otherwise have.
Unlike an internal rooflight conversion, a dormer changes the outside shape of your roof, so it may also need planning permission depending on its size, position and your property. For how a dormer conversion actually works, from opening the roof to the finished room, see our dormer attic conversions guide, or read the detail on planning permission.
Dormer Cost FAQs
Common questions, answered straight
It depends on your roof. Where head height is already good, a rooflight conversion is usually the better value because it leaves the roof largely in place. Where head height is tight, a dormer is often the only way to get a room that meets habitable standards, and in that case the extra cost is buying you usable space you could not otherwise have. We measure up and tell you honestly which route your home actually needs.
It can. A rear dormer is often the more straightforward of the two, while a side dormer may involve the gable, party lines and different access, all of which can add work. Size and finish still matter more than position on their own, so the honest comparison is done on your specific roof rather than by rule of thumb.
Sometimes. Unlike an internal rooflight conversion, a dormer changes the outside shape of your roof, so whether it needs permission depends on its size, position and your property. Building regulations always apply either way. We confirm your specific situation at the assessment; for the detail, see our planning permission guide.
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