House Extensions Lewisham

GS Renovation plans and builds extensions across Lewisham, adding space to the bay-fronted Victorian and Edwardian terraces of Catford, Forest Hill and New Cross. We handle everything from foundations and steel to the final fit-out, whether your project runs as permitted development or needs a full planning application.

In Lewisham, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Lewisham: the structural engineer we appoint designs the structure, we build it, and building control signs it off.

Side-return and rear extensions in Lewisham

The side return, that narrow strip beside the rear closet wing, is the most valuable space on a Lewisham terrace. Filling it in widens a cramped galley kitchen into a proper kitchen-diner running the full width of the house. We dig new foundations to suit the ground and any nearby trees, tie the new brickwork into the existing wall, and carry the original structure on a steel beam where the outside wall comes out.

A rear extension pushes the back of the house into the garden, often combined with the side return as a wrap-around. On these terraces we usually add generous rooflights or a lantern to bring daylight deep into the plan, since the middle of a terrace can be dark. Bi-fold or sliding doors open the new room to the garden. We manage the roof works, insulation and weathering so the extension is warm, dry and built to current standards.

Housing in Lewisham

On the valuation list Lewisham counts about 133,910 homes, 60% flats and 40% houses; 34% predate 1919, 18% are interwar and 45% post-war. Where most homes are flats, a flat in Lewisham has no householder permitted development rights, so extending one needs planning permission and the freeholder's consent.

Sewers, full plans and scale for a Lewisham rear extension

Lewisham uses a full plans application for any new proposal to build above or within 3 metres of a drain or sewer. Behind a Lewisham terrace the drain from the house and the shared run collecting from its neighbours can both sit close to where a rear extension goes, so check this before assuming the quicker route will do. On a full plans application Lewisham Building Control sends its decision within five weeks, unless the applicant has given a three week extension. That period belongs in the programme, and it is the reason we lift the inspection chamber covers at the first visit and have unclear runs traced by camera.

The Lewisham Local Plan says extensions to residential buildings should normally be subordinate in scale to the original building. For a Lewisham terrace with a two storey back addition, that becomes a real test when a wrap-around or a first floor rear extension is drawn. The new part should read as smaller than the house it is attached to, not as a second house built on the back. We price and programme from drawings that already respect that test, so the planning application is not redrawn halfway through and the structural engineer we appoint designs the steel once rather than twice.

Planning and permitted development across Lewisham

Many single storey rear and side-return extensions in Lewisham fall under permitted development, meaning no full planning application, though a lawful development certificate from Lewisham Council is worth having for certainty and a future sale. Size limits, height and how close you build to the boundary all matter. Double storey extensions and anything facing the street usually need planning permission. In a conservation area, side extensions, including a side-return infill, and two-storey rear extensions lose their permitted development rights, while a single-storey rear extension within the limits keeps them unless an Article 4 direction says otherwise. A listed building needs listed building consent. A single-room addition, such as a ground-floor rear room for a kitchen or a playroom, follows the same rules as any other room extension.

Parts of Blackheath, Brockley, Telegraph Hill and the streets around the Horniman Museum sit in conservation areas, where the council looks closely at materials and appearance. Whichever route applies, the build itself must meet building regulations, covering foundations, structure, insulation, fire safety and drainage, all inspected by building control. We advise early on the likely route for your address, work with your architect or designer on the drawings, and give you what you need for the party wall notices you serve where the extension affects a shared boundary.

Kitchen extensions in Lewisham

60% of homes in Lewisham are flats, and a flat has no householder permitted development, so a ground-floor flat's kitchen extension needs planning permission from Lewisham Council and the freeholder's consent. Most kitchen extensions here are on the 40% of homes that are houses. The fit-out is priced on its own page, kitchen renovation in Lewisham; the build figures are in the table above.

Double storey extensions in Lewisham

Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Lewisham often needs planning permission from Lewisham Council. On the 31% of homes that are terraced, the neighbours' windows usually decide the depth. Lewisham says flats or subdivided houses in conservation areas do not have permitted development rights and must seek planning permission for changes to the exterior (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.

• Side-return and rear extensions
• Single and double storey extensions
• Drawings and the structural engineer's design coordinated for you

VOA Council Tax stock of properties, March 2025, for all 37 statistical areas in Lewisham. Counts rounded by the VOA.

Once you know the scope of the house extensions in Lewisham, it helps to read RSJ and steel beam installation in Lewisham, our Lewisham area guide, double storey extensions, garage conversions in London, house extensions across London and Party Wall Act Explained.

Why Choose GS Renovation in Lewisham

Homeowners across SE4, SE13 and SE23 choose GS Renovation because we take an extension from first sketch to finished room as one team. We advise honestly on planning versus permitted development, build the structure to the design of the engineer we appoint, and give you what the party wall process needs. With our founder's 30+ years on the tools, you deal with one accountable contractor throughout.

• Brick and mortar matched to the existing elevation
• Weathertight shell reached before the fit-out begins
• Fully insured, with cover in place on every site

Reviewed jobs near Lewisham

1 MyBuilder review from Crofton Park, with each customer's own job title:

• Replace small section of wooden worktop, sink, tap and gas hob, Crofton Park, 17 Apr 2024 (5 out of 5)

Read all 31 on our reviews page.

Checked by Abdelaaziz Saaid, founder and director of GS Renovation Ltd (Companies House no. 14611254). Structural design is by the consulting engineer appointed to your project.