Dormer loft conversion cost in London: what the design stage costs
Our fixed fee for rear dormer loft conversion drawings starts at £695, and at £745 for an L-shaped dormer. The builder's price is separate and depends on the roof, the structure and the finish. We hold no sourced build figure for London, so this page prices the drawings and the rules that shape them.
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Two dormer layouts, two starting fees
A rear dormer is the simplest layout and our permitted development drawings for one start at £695. An L-shaped dormer starts at £745. Both are published prices, and both are starting points rather than quotes.
If the project needs planning and building regulations drawings together, our fixed fee range for that package is £1,845 to £3,145.
The volume limit that decides the dormer's size
Under Class B of the General Permitted Development Order a roof addition may add up to 40 cubic metres to the roof space of a terrace house, and up to 50 cubic metres in any other case (GPDO 2015, Schedule 2, Part 1).
The limit measures the volume you add, so our drawings work out the figure before anyone orders materials. Read the permitted development explainer for the other limits.
Under Class B of the General Permitted Development Order a roof addition may add up to 40 cubic metres to the roof space of a terrace house, and up to 50 cubic metres in any other case (GPDO 2015, Schedule 2, Part 1).
Proving it with a certificate
A certificate of lawful development for a proposed operation costs half the full application fee, which is £274 for a householder project from 1 April 2026. It gives written confirmation that the dormer would be lawful.
Our lawful development certificate drawings service prepares the plans the certificate needs.
Dormer or another loft style
A dormer is one of several shapes. Compare it with the others in our guide to loft conversion types, or see what a dormer costs to draw on the dormer loft conversion drawings page.
Whether a loft conversion needs planning consent at all is set out in our guide to planning permission for a loft conversion.
Sources
Every figure on this page, where it comes from and a link to the original.
| Figure | Source | Link |
|---|---|---|
| £695 | DrawingsDirect starting fixed fee for rear dormer loft conversion permitted development drawings, from the published price list | drawingsdirect.co.uk |
| £745 | DrawingsDirect starting fixed fee for L-shaped dormer loft conversion permitted development drawings, from the published price list | drawingsdirect.co.uk |
| £1,845–£3,145 | DrawingsDirect fixed fee range for planning and Building Regulations drawings | drawingsdirect.co.uk |
| 40 cubic metres | GPDO 2015 Sch 2 Pt 1 Class B.1(d)(i): roof additions may add up to 40 cubic metres to the roof space of a terrace house (source wording: "40 cubic metres in the case of a terrace house") | www.legislation.gov.uk |
| 50 cubic metres | GPDO 2015 Sch 2 Pt 1 Class B.1(d)(ii): roof additions may add up to 50 cubic metres to the roof space of any other house (source wording: "50 cubic metres in any other case") | www.legislation.gov.uk |
| £274 | Fees for planning applications in England from 1 April 2026 (MHCLG, SI 2012/2920 as annually indexed): certificate of lawful development for a proposed use or operation is half the full application fee; for a householder project that is half of £548 (source wording: "Half the Full Application fee"; the £274 is our arithmetic) | assets.publishing.service.gov.uk |
Questions people ask
How much does a dormer loft conversion cost in London?
How big can a dormer be without planning permission?
Can I prove a dormer is lawful before I build it?
Photographs: David Hawgood (CC BY-SA 2.0).
