House Extension Builders in London

Rear Extensions

The most common extension in London, and the starting point for most projects.

A rear extension adds depth to the back of the property, most often to enlarge the kitchen and create an open-plan living and dining space. It is usually the simplest extension type to secure under permitted development, and the one most London homeowners consider first.

Side Return Extensions

Reclaiming the alley beside a Victorian terrace.

Common on London's Victorian and Edwardian terraces, a side return extension builds into the narrow side passage running alongside the kitchen, squaring off the rear of the house. It is typically combined with a rear extension for a full-width kitchen and living space.

Wraparound Extensions

Side return and rear extension, resolved as one continuous space.

A wraparound extension combines the side return and rear extension into a single structure, maximising floor area at ground level. It typically requires full planning permission rather than permitted development, since the combined footprint exceeds the volume allowances available to either extension type alone.

Double-Storey Extensions

Extending the ground floor and the floor above it, in one project.

A double-storey extension adds space to both the ground and first floor in a single build. It is typically the most structurally complex extension type, and the one requiring the most careful integration with the existing roofline and window arrangement, but it is also the most cost-efficient way to add two rooms, since groundworks and scaffolding are shared across both floors.

Kitchen Extensions

The most searched extension in London, and rarely a standalone structural type.

Most kitchen extensions are delivered as a rear, side return or wraparound extension, designed specifically around the kitchen and adjoining living space. Sovran designs the extension and the kitchen as one project, so the structural opening, the roof glazing and the bespoke cabinetry are resolved together rather than handed between separate contractors.

Cost per m² by Extension Type

Across most extension types, London costs run from £2,500 to £5,000+ per square metre, with high-end architect-designed projects exceeding £6,000 per square metre in prime boroughs. As a guide:

• Rear extension: £80,000–£200,000+ — the most common extension type
• Double-storey extension: £120,000–£300,000+ — reflecting the added structural complexity
• Side return and wraparound extensions: £90,000–£220,000+ — depending on the extent of the side return and whether the project is combined with a rear extension

For an indicative figure against your own property, use the cost calculator.

What Drives the Price at the Luxury End

Within each extension type, the range is set by structural complexity, glazing specification and finish. Full-width structural glazing, a steel portal frame to open up the existing house, bespoke kitchen joinery, and integrated climate or smart-home systems all move a project toward the top of its range. At Sovran, every quote is fixed before work starts, so the number agreed at contract stage is the number paid at handover, not a starting estimate that grows with the build.

Permitted Development for Rear & Side Extensions

Single-storey rear extensions can typically extend up to 4 metres for detached houses and 3 metres for all other house types under standard permitted development, or further under the Neighbour Consultation Scheme where neighbours do not object. Side extensions are usually limited to half the width of the original house. A wraparound extension, or any double-storey extension, generally exceeds these allowances and requires full planning permission.

Conservation Areas and Listed Buildings in London

Permitted development rights are reduced or removed entirely across many of London's conservation areas, and further restricted on listed buildings, where even internal alterations can require consent. Sovran assesses the planning position for every property before design work begins, so the extension is designed to what the site can actually achieve rather than redesigned after a refusal.