First-floor extensions in Canonbury
Our first-floor extensions service in Canonbury covers everything: measured survey, design, planning or permitted development checks, structural design, building control and the build itself.
Quick reference for homeowners in Canonbury.
- Postcode districts
- N1
- County / area
- Greater London, England
- Price region
- London
- Guide price
- £30,000–£43,500 (£2,160–£3,120 per m²)
- Approval route
- It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
- Nearest towns
- Highbury (0.6 miles), Islington (0.7 miles), Barnsbury (1.1 miles)
- First visit
- Free, no obligation
About a first-floor extension
A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe. It adds a bedroom, bathroom or study without enlarging the footprint. Whether it works depends mainly on whether the walls and foundations below can carry the extra load.
We cover Canonbury (N1) and the places around it, including Highbury (0.6 miles), Islington (0.7 miles) and Barnsbury.
What it costs in Canonbury
Expect a first-floor extension in Canonbury to land somewhere around £30,000–£43,500 for 4 m × 3.5 m of new first-floor space (14 m²). Our London guide rate is £2,160–£3,120 per m², including VAT. Kitchens, bathroom fittings and flooring are priced separately so you can compare like with like.
| Spec | Per m² | 4 m × 3.5 m of new first-floor space (14 m²) |
|---|---|---|
| Essential | £1,990–£2,870 per m² | £28,000–£40,000 |
| Standard | £2,160–£3,120 per m² | £30,000–£43,500 |
| Premium | £2,590–£3,740 per m² | £36,500–£52,500 |
Planning and building regulations in Canonbury
In England, adding a first floor turns a single-storey extension into one of more than one storey. To be permitted development, the extension as a whole must go no more than 3 m beyond the rear wall of the original house and stay at least 7 m from the rear boundary, with matching materials and roof pitch. Over a side extension it always needs planning permission, costing £548 (or £575 for applications made from 8 December 2026).
Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.
Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.
Design points for Canonbury homes
Tying into the house
The new floor and walls must line up with the existing first floor, often through a new opening in the rear wall above the old one. Floor levels, the position of upstairs windows and the existing roof all affect where the opening can go, so we survey both floors carefully.
Escape and fire safety
A new first-floor bedroom needs an escape window with a clear opening of at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom no more than 1,100 mm above the floor, unless there is a protected route to the stairs.
How we'd run your project
Visit and first ideas
One of our team visits your house in Canonbury, checks the walls, roof and drains, and sketches out options with you.
Get it approved
Once you're happy with the design we submit it to the council for Canonbury and deal with any questions from the planning officer.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.
Questions about first-floor extensions in Canonbury
How much does a first-floor extension cost in Canonbury?
Our guide for London, which covers Canonbury, is £2,160–£3,120 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £30,000–£43,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
Which postcodes do you cover around Canonbury?
We cover Canonbury (N1) and nearby places including Highbury, Islington and Barnsbury, plus the rest of Greater London. The first site visit is free.
Do I need planning permission for a first-floor extension in Canonbury?
Canonbury is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.
Will the first-floor extension match my house?
It should, and in England matching materials and roof pitch is a condition of permitted development. We match brick, tile, mortar colour and window style where we can, and tell you at the design stage if an exact brick match is not available, so you can choose between the closest match and render or cladding.
What happens to the room below while the first floor is built?
The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.
Nearby
The same service in neighbouring towns:
Other extensions in Canonbury
- Rear
- Side
- Wraparound
- Part two-storey
- Over a garage
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Canonbury · First-floor extensions across Greater London
Book a free site visit in Canonbury and we'll tell you what's possible, what approvals you need and what the design stage would cost.