Types of House Extension — Which Is Right for Your Property?

A rear extension extends the property into the rear garden. It is the most common extension type in London. The extension is typically single storey (at ground floor level) and usually contains a kitchen-diner, living space, or both.

• Planning position:
• •Up to 4 metres deep: permitted development for terraced and semi-detached houses
• •Up to 4–6 metres deep: Prior Approval required (neighbour consultation scheme)
• •Up to 8 metres deep: Prior Approval for detached houses (4–8m range)
• •Beyond these limits: full planning permission required

• Typical features:
• •Flat roof or pitched roof with roof lantern or skylights
• •Bifold or sliding glass doors to garden
• •Structural opening through existing rear wall
• •Underfloor heating (very common)
• •New kitchen as part of the fit-out

Typical cost: £45,000 – £90,000 Typical programme: 10–14 weeks on site

A side return extension fills in the narrow alleyway that runs beside many Victorian and Edwardian terraced houses. The 'side return' is typically 1–2 metres wide and can run the full depth of the existing kitchen or rear of the house. When combined with a rear extension, it creates an L-shape or wraparound.

• Planning position:
• •Usually within Permitted Development if less than half the width of the original house
• •Full planning required if in a Conservation Area or exceeds PD limits

• Key features:
• •Glazed roof (structural glass or polycarbonate) to bring light into the resulting space
• •Roof lantern over the combined rear/side area
• •Often combined with rear extension for a wraparound result
• •Common in East and South London Victorian stock

Typical cost (side return alone): £35,000 – £65,000 Typical programme: 8–12 weeks

A wraparound extension combines a rear extension with a side return, creating an L-shape or full wraparound footprint. This delivers the maximum ground-floor footprint increase without a double-storey addition. The result is typically a large open-plan kitchen-diner-living area at the rear and side.

• Planning position:
• •Often requires full planning permission (the combined volume frequently exceeds PD limits)
• •In Conservation Areas, always requires planning permission

• Typical features:
• •Open-plan kitchen-diner (most common use of the resulting space)
• •Bifold or sliding doors to garden
• •Roof lanterns over the side return area
• •Structural steel frame (RSJ beams) to create large open-plan spans
• •Underfloor heating throughout

Typical cost: £65,000 – £120,000 Typical programme: 14–18 weeks

A double-storey extension adds floor area on both the ground and first floors. It is typically built at the rear or side of the property and can contain a bedroom and bathroom on the first floor and a kitchen, living room, or utility room on the ground floor.

• Planning position:
• •Almost always requires full planning permission (most PD limits apply to single-storey extensions only)
• •The rear wall of the upper storey must not be closer than 7 metres to the rear boundary for PD

• Typical features:
• •Bedroom and ensuite on first floor
• •Kitchen-diner on ground floor
• •Matching external materials (brick and roof tiles)
• •Larger structural implications than single-storey

Typical cost: £80,000 – £150,000 Typical programme: 16–24 weeks

A kitchen extension is a specific form of rear (or side) extension built primarily to house a new kitchen. Many London homes have a small original rear kitchen that is extended to create an open-plan kitchen-diner. The planning position is the same as for a standard rear extension.

• Key considerations:
• •The structural opening between the existing house and new extension (typically a large steel beam or RSJ)
• •New kitchen units are almost always supplied by the client (RCB installs labour only for client-supplied kitchens)
• •Gas and electricity supply routes to the new kitchen location
• •Extraction hood ventilation route (through the wall or over the roof)
• •Underfloor heating is extremely common in kitchen extensions

Typical cost (extension only, kitchen supplied by client): £45,000 – £85,000

A complete extension package from RCB includes:

• •Structural engineer design (foundations, steels, roof)
• •Building Regulations application and inspections managed
• •Scaffold (where required)
• •Groundworks and foundations
• •External walls (cavity wall construction, matching brickwork)
• •Roof structure (pitched or flat)
• •Roof windows or lantern (if specified)
• •External windows and doors
• •Structural opening through existing rear wall (steel beam, temporary support, making good)
• •Internal walls and partitions
• •First-fix plumbing and electrical
• •Insulation (walls, floor, roof) to Building Regs Part L standard
• •Underfloor heating (if specified)
• •Screed over underfloor heating
• •Plasterboard and skim throughout
• •Bathroom or WC installation where included (labour only — client supplies suite)

• Exclusions:
• •Kitchen units, appliances, worktops, tiles (client-supplied)
• •Second-fix materials (tiles, sanitaryware, light fittings, floor finishes — client-supplied)
• •Carpet — RCB does not supply or install carpet
• •Architect and Planning Application fees
• •Party wall surveyor fees (where applicable)
• •Furniture and decoration after practical completion

House extensions almost always trigger associated works:

• •Kitchen renovation — the main reason for most ground-floor extensions
• •Utility room creation — extremely common in side returns
• •WC / cloakroom addition — very common in larger extensions
• •Ground floor open-plan reconfiguration — structural wall removal to create open plan
• •Bifold and sliding door installation
• •Structural opening creation (new RSJ beam from existing house into extension)
• •Underfloor heating throughout the ground floor
• •Ground floor refurbishment (all floors, decoration, skirting, doors) while trades are on site

RCB prices the extension and associated works as one integrated scope — one fixed price, one programme, one team.