House Extension Cost in London 2026: Rear, Side Return and Wrap-Around
What does a house extension cost in London in 2026? Full pricing breakdown for rear, side return and wrap-around extensions — with planning notes, what's included and how to compare quotes.
A rear extension is London’s most popular home improvement. Done right, it transforms a dark Victorian terrace into a contemporary open-plan home — and adds substantially more value than it costs.
This guide sets out real 2026 costs from 2VP’s completed projects.
Extension Costs at a Glance (London 2026)
| Extension Type | Typical London Cost | Notes | |---|---|---| | Single-storey rear (small, ≤15m²) | £45,000 – £80,000 | Infill or modest addition | | Single-storey rear (standard, 20–30m²) | £78,000 – £140,000 | Most common; open-plan kitchen | | Side return only | £55,000 – £90,000 | Narrow infill; big impact on light | | L-shaped (rear + side return) | £95,000 – £165,000 | Full open-plan transformation | | Wrap-around | £110,000 – £185,000 | Maximum ground-floor footprint | | Double-storey rear | £120,000 – £200,000 | Adds bedroom above kitchen |
All prices include design, structure, building regs, labour, materials and VAT. Kitchen and fitted furniture are not included unless specified.
What Makes a House Extension Cost More?
Size
Cost per m² tends to decrease as extension size increases — fixed costs (groundworks, roof structure, steelwork) are spread across more usable area.
Structural complexity
Most Victorian terraced homes have shallow strip foundations. If ground conditions require piled foundations, costs increase by £8,000–£15,000. Basement extensions are a different product category entirely.
Glazing specification
The biggest single variable in an open-plan extension budget is the rear glazing. Standard aluminium bifold doors (3m–4m opening): £3,500–£6,000. Premium sliding glass doors with structural glass roof: £12,000–£22,000. Full-width rooflights and structural glazing can add £15,000–£30,000 to the project.
Kitchen and finishes
2VP builds the shell and services. What you spend on kitchen installation, worktops and appliances is separate — plan £20,000–£60,000 for a quality kitchen in a London extension.
Postcode uplift
As with loft conversions, prime London postcodes carry a 20–40% cost premium over outer boroughs — driven by labour rates, access constraints and specification expectations.
The Victorian Side Return: London’s Most Overlooked Space
Most Victorian terraced homes in Fulham, Chelsea, Battersea and Clapham have a narrow passage running alongside the ground floor — typically 900mm to 1.5m wide. It’s usually wasted space: a dark corridor to the garden.
A side return extension fills this passage, pushing the rear of the house to the full width of the plot. Combined with a rear extension (an L-shape), it:
- Doubles the ground-floor width at the kitchen end
- Maximises natural light with a large rooflight running the full length of the extension
- Creates a genuine open-plan space — kitchen, dining and living in one continuous room
The side return element itself typically costs £55,000–£90,000 as a standalone project. As part of an L-shaped extension, the additional cost of incorporating the side return is proportionally lower (the mobilisation, groundworks and roof are already priced for the rear extension).
Planning Permission for Extensions in London
Permitted Development
A single-storey rear extension up to 3m (semi-detached or terraced) or 4m (detached) depth, maximum 4m height, can proceed under Permitted Development Rights — no planning application, just a Certificate of Lawful Development.
The Neighbour Consultation Scheme (Prior Approval) extends this to 6m (semi-detached/terraced) or 8m (detached) for single-storey extensions.
When you need Full Planning Permission
- The extension is to the side elevation visible from the street
- You want a double-storey extension (side or rear)
- The property is in a conservation area or Article 4 Direction area
- The property is listed
2VP manages the full planning process in-house.
What’s Included in a 2VP Extension Contract?
A typical fixed-price 2VP extension contract covers:
Pre-contract
- Measured survey and topographical survey
- Architectural drawings for building regulations
- Structural engineer’s calculations and specifications
- Planning application (if required)
- Building regulations submission and approval
- Party wall notice service
Structure and fabric
- Excavation and new foundations
- New structural walls (brick, block or structural frame)
- Steel beams and posts
- Roof structure: flat roof (warm deck) or pitched
- External windows and doors (aluminium as standard)
- Insulation to Part L
Services
- Extend central heating (new radiators, underfloor heating if specified)
- Electrical first and second fix
- New WC if included in the scheme
Finishes
- Plasterboard and skim throughout
- Floor screed or timber deck ready for floor finish
- Internal paint (white as standard)
Not included: kitchen, furniture, flooring finish, external landscaping.
How to Read a Quote
When comparing extension quotes, ensure you are comparing like-for-like:
- Structural glazing included? Many “low” quotes price sliding doors at minimum spec. Ask what bifolds or sliders are specified.
- Is underfloor heating included? Often priced separately.
- What foundation depth is assumed? If the quote doesn’t mention a site investigation, it may be assuming easy conditions that your site doesn’t have.
- Is the kitchen included? Almost never — but confirm.
- Is VAT included? Standard extensions are subject to 20% VAT.
2VP’s quotes are fixed-price JCT Minor Works contracts with a 10% contingency included for unforeseen ground conditions. What we quote is what you pay.
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