First-floor extensions in New Cross

Quick reference for homeowners in New Cross.

Postcode districts: SE8 and SE14
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: Brockley (0.8 miles), Greenwich (1.2 miles), Peckham (1.4 miles)
First visit: Free, no obligation

About a first-floor extension

A first-floor extension suits you if your house already has a single-storey extension and you need more space upstairs. You get a structural check of the existing walls and foundations, a design that ties the new floor into the house, the approvals your nation needs, building regulations approval and the build, managed by us and carried out by vetted teams working under S&K.

Around New Cross we also work in Brockley, Greenwich and Peckham, and across the rest of Greater London. Postcode districts in and near New Cross: SE8 and SE14.

What it costs in New Cross

Expect a first-floor extension in New Cross 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. These are guides, not quotes. Ground conditions, steelwork and access can move the figure either way.

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 New Cross

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 New Cross homes

Matching the roofline

A first-floor extension often changes how the back or side of the house looks more than the original single storey did. Matching the main roof pitch and materials, and keeping the ridge below the main ridge, usually gives the best result and is expected for permitted development in England.

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 New Cross, checks the walls, roof and drains, and sketches out options with you.
Design and approvals
We draw the extension and check it against the rules for England, then apply for planning permission or a certificate of lawfulness, whichever fits.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
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 New Cross

Who handles building regulations for a project in New Cross?

We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.

How much does a first-floor extension cost in New Cross?

Our guide for London, which covers New Cross, 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 New Cross?

We cover New Cross (SE8 and SE14) and nearby places including Brockley, Greenwich and Peckham, plus the rest of Greater London. The first site visit is free.

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.

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.

Nearby

Nearby towns we cover for first-floor extensions:

Other extensions in New Cross

All two-storey extension services in New Cross · First-floor extensions across Greater London

Send us your postcode and a few details. We'll get back to you to arrange a visit and talk through your options.