Service

House Extension in London

A well-designed extension transforms how a London house lives — not just how it looks. We have built side returns, rear extensions, wrap-arounds, double-storey side extensions and conservatory replacements across East and South East London for two decades. Each one delivered on programme, signed off first time, with the snagging closed inside two weeks.

Types of house extension we build

Side-return extensions on Victorian terraces give the most useful added space per pound spent — typically 8 to 14 square metres added to the kitchen, with full-width sliding glass doors onto the garden. Rear extensions widen the back of the house and are common on inter-war semis in Walthamstow, Winchmore Hill and Wanstead. Wrap-around extensions combine side return and rear into one open-plan kitchen-dining-living space. Double-storey side extensions add a bedroom and bathroom upstairs as well as kitchen space below. Conservatory replacements remove old polycarbonate or single-glazed structures and replace them with insulated brick-and-glass extensions that are habitable year-round.

Permitted development versus planning permission

Most single-storey rear extensions on terraced houses fall under permitted development rules and do not require planning permission. Wrap-arounds and double-storey extensions almost always require planning. Conservation areas and listed buildings always require planning. The architect typically guides this decision, but we work alongside them on viability and budget while the application is being prepared.

Building control and party wall

Every extension requires a building control application, structural engineer calculations and (where the extension is on or near the boundary) a party wall agreement with the adjoining owner. We submit and manage all of these. Building control inspections happen at foundation, damp-proof course, pre-plaster and completion stages. Most of our extensions pass first inspection at every stage.

Glazing, structural openings and finishes

The defining feature of a modern London extension is usually the glazing — full-width aluminium or steel-framed sliding doors, lantern roof lights, Crittall-style internal screens. We work with several London-based fabricators (IQ Glass, Origin Frames, Schueco) and quote glazing as a separate line item so you can choose between performance and budget. Structural openings into the existing house (typical on side returns and wrap-arounds) require a steel beam supported on padstones, calculated by a structural engineer and inspected by building control.

Frequently asked questions

How long does an extension take?

A standard side-return extension on a Victorian terrace runs 8 to 12 weeks on site. A wrap-around runs 12 to 18 weeks. A double-storey extension runs 16 to 22 weeks. Programme is set at contract signing.

What is the typical cost per square metre?

In 2026 prices, £3,200 to £4,800 per square metre for a single-storey extension finished to a high domestic standard (excluding kitchen units and appliances). Double-storey extensions are roughly 1.7 times the single-storey rate per square metre because most of the cost is foundations, glazing and finishes.

Will I lose the kitchen during the build?

Yes, for typically 6 to 9 weeks if the extension involves the kitchen. We can install a temporary kitchen in another room (utility, dining room) at the start of works and most clients find that workable.