Extension types explained

London homes can be extended in several ways. The right choice depends on your property layout, budget, and planning constraints.

Rear extension

The most common type. A single-storey rear extension projects from the back of the house, typically creating a larger kitchen-diner. Under Permitted Development, you can extend up to 6 metres (semi/terrace) or 8 metres (detached). Our extension drawing service starts from £840.

Side return extension

Absorbs the narrow alleyway running along the side of a terraced house. Typically combined with a rear extension to create an L-shaped or full-width ground floor. See our Camden side return case study.

Wraparound extension

Combines side return and rear extension into a single structure. Creates the largest open-plan space. Usually requires full planning due to size. See our Wandsworth wraparound case study.

Double-storey extension

Extends at both ground and first floor. Costs 50–70% more than single-storey (not double — foundations and roof are shared). Always requires planning.

Flat roof extension

Most single-storey extensions in London use a flat roof with single-ply membrane. Rooflights bring light into deep plans.

Kitchen extension

The most popular reason for extending — a larger kitchen-diner. Expect £1,800–2,800/sqm for construction plus drawing fees from £840.

London extension costs (2026)

  • Single-storey rear: £1,800–2,800 per sqm (construction)
  • Double-storey: £2,500–3,500 per sqm
  • Side return only: £2,000–3,000 per sqm
  • Wraparound: £1,900–2,600 per sqm
  • Drawing fees: from £840 (Essentials) or £1,750 (Complete) — see pricing

Planning permission rules

Many single-storey rear extensions fall under Permitted Development. Key limits: 6m (semi/terrace) or 8m (detached), 4m max height, matching materials. Conservation areas and Article 4 Directions typically require full planning.

We recommend a Lawful Development Certificate (£129) for any PD project. Read our planning permission guide.

Structural considerations

Most extensions require at least one RSJ beam. Our packages include structural engineer coordination. See our building regulations service.

Party Wall

If your extension involves work within 3 metres of a neighbour’s foundation, the Party Wall Act 1996 requires formal notices at least two months before work. Applies to most side return and rear extensions on terraced properties.

Borough cost comparison

Inner vs outer London (20sqm extension)

Inner London
£50k–70k
Outer London
£38k–52k
Drawing fee
From £840

Browse extension services by borough:

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