Cost guide · North London
Loft conversion costs in North London (2026)
That empty space over your head could be your best room. Here's what it really costs to get up there, from lofts we design across Barnet, Camden, Haringey, Brent and Harrow.
Written by Dor Cohen, RIBA Chartered Architect, ARB Registered
Last updated
How much does a loft conversion cost in North London?
A typical rear dormer loft conversion in North London, with a bedroom and en-suite of about 20–30 m², costs £45,000–£65,000 to build, excluding VAT and fees. That works out at roughly £2,000–£2,500 per m² before luxury finishes. Hip-to-gable and mansard conversions usually cost 15–25% more. Budget on top for 20% VAT, £3,500–£5,000 of consultant fees and a 10% contingency.
Build cost by type and size
A rear dormer is the simplest: a box-shaped room built out from the back slope. Builders typically charge £2,000–£2,500 per m² before luxury finishes.
Hip-to-gable (common on 1930s semis) and mansard lofts (common on terraces) cost 15–25% more, because there's more structure to rebuild.
| Size | Rear dormer | Hip-to-gable / mansard |
|---|---|---|
| 20 m² | £40,000–£50,000 | £46,000–£62,500 |
| 25 m² | £50,000–£62,500 | £57,500–£78,125 |
| 30 m² | £60,000–£75,000 | £69,000–£93,750 |
| 35 m² | £70,000–£87,500 | £80,500–£109,375 |
| 40 m² | £80,000–£100,000 | £92,000–£125,000 |
Excluding VAT. A typical bedroom and en-suite dormer comes to £45,000–£65,000; bigger or higher-spec lofts often £60,000–£85,000.
The costs on top of the build
Consultants usually add up to about £3,500–£5,000 in total. Here's where it goes.
| VAT on the build | 20% of the builder's price, if they are VAT registered |
|---|---|
| Contingency | 10% of the build cost |
| Structural engineer | £1,200–£2,000 |
| Building Control | £1,000–£1,400 |
| Party wall surveyor | £1,000–£1,500 per neighbour, if they appoint their own |
| Lawful Development Certificate or planning fee | Paid to the council; check the Planning Portal for the current amount |
| Architect: survey, 3D model and concept design | £2,600 / £3,250 / £4,250 (Essential / Complete / Signature)* |
| Architect: planning drawings, only if needed | from £1,800* |
*Our estimated fees for a 2–3 bed semi with a loft conversion. .
Budget builder
Rough whole-project budget
- Build (25 m²)£50,000–£62,500
- Contingency (10% of build)£5,000–£6,250
- Structural engineer£1,200–£2,000
- Building Control£1,000–£1,400
- Party wall surveyor (1 neighbour)£1,000–£1,500
- Architect: survey, 3D model and concept design£3,250
Total, excluding VAT
£61,500–£77,000
VAT at 20% on the build adds about £10,000–£12,500. Planning or certificate fees not included. Architect fee uses our Complete package for a 2–3 bed semi.
The surprises that catch people out
- The new staircaseThe stairs have to land somewhere, ideally above the existing ones, with enough headroom. Finding that space can mean rearranging the floor below.
- Fire regulationsA third storey means fire doors on the escape route, mains-wired smoke alarms and sometimes other upgrades to the rest of the house.
- Steel beamsSteel beams are usually craned in over the roof, with posts down to the first floor. Removing chimney breasts adds more.
- Boiler and water pressureA top-floor shower needs good pressure, which often means a new hot water cylinder or boiler.
Planning or permitted development?
Roughly half of the lofts we design in North London go through as permitted development, which allows up to 40 m³ of extra roof space on a terrace and 50 m³ on a semi or detached house. We recommend a Lawful Development Certificate, so you have proof when you come to sell.
The other half need planning permission: homes in conservation areas (there are lots in Camden, Haringey and Hampstead Garden Suburb), flats, and mansards or dormers facing the street. Check your address.
Settle the stairs, headroom and design before builders price it. Changes once building starts are one of the biggest risks to your budget. There will always be some unexpected costs on an existing house, but none should come from the design.
How long it takes
Allow 6–7 months in total: about 3–4 months for design and approvals, then 8–12 weeks on site.
Modelling your roof in 3D from a scan shows exactly where you can stand up, before anyone picks up a saw.
Scan and 3D model
A Matterport scan of your home becomes an accurate 3D model, roof and all, without a survey visit to book.
Concept design
We test the stairs, headroom and layout in 3D and review options with you on video calls.
Lawful Development Certificate or planning
Around half of North London lofts are permitted development. The rest need planning, usually decided within 8 weeks of validation.
Technical drawings and builder prices
Building Regulations drawings and engineer's design, so builders can price like for like.
On site · 8–12 weeks
Most lofts take 8–12 weeks to build, 6–7 months in total from first sketches.
Questions
Everything you need to know about working with DOR Architects.
A typical rear dormer with a bedroom and en-suite costs £45,000–£65,000 to build, excluding VAT. Bigger or higher-spec lofts of 30–40 m² often come to £60,000–£85,000.
Yes. Expect to pay 15–25% more than a rear dormer, because of the extra steelwork, rebuilding the side wall or roof slope, and more party wall work on a mansard.
About half of the lofts we design in North London are permitted development, using the volume allowance of 40 m³ on a terrace or 50 m³ on a semi or detached house. We recommend getting a Lawful Development Certificate to prove it. Conservation areas, flats and roof changes facing the street usually need full planning permission.
The usual surprises are the new staircase (and finding headroom for it), fire doors and fire safety upgrades to the rest of the house, steel beams craned in over the roof, and a new hot water cylinder or boiler so the top-floor shower has decent pressure.
Allow 6–7 months in total: around 3–4 months for design and approvals, then 8–12 weeks on site. You can usually stay living at home for most of the build.
For a 2–3 bed semi with a loft conversion, our estimated fee for the survey, 3D model and concept design is £2,600 (Essential), £3,250 (Complete) or £4,250 (Signature). Planning drawings, only if needed, are from £1,800.
Usually yes, at 20%, if your builder is VAT registered. Our build figures exclude VAT, so add it on when you set your budget.
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