Size and footprint
More floor area means more foundations, structure, roofing and finishes.
London extension cost guide
How Much Does a House Extension Cost in London?
Typical London projects range from £55,000 – £100,000+ for a side return to £100,000 – £190,000+ for a double-storey extension, including VAT.
These are indicative ranges, not quotations. Your home, structure, access and finish determine the final cost.
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The direct answer
Typical London extension cost ranges
These indicative ranges provide an early budget position for a standard specification. They are not a formal quotation and should not be reduced to a single cost-per-square-metre rule.
Rear extension£60,000 – £120,000+ including VAT
Side return extension£55,000 – £100,000+ including VAT
Wraparound extension£80,000 – £160,000+ including VAT
Double-storey extension£100,000 – £190,000+ including VAT
Typical project investment: approximately £60,000-£120,000+ including VAT. Size, structure, glazing, location and fit-out can move the project outside this range.
What moves the cost
The label describes the shape. The property and the specification decide where the work sits within the range.
Structure and drainage
Steelwork, ground conditions and existing drains can materially change the build.
Access and glazing
Restricted terrace access and larger glazed openings affect labour, handling and structure.
Specification
Doors, rooflights, flooring, joinery and finishes determine where a project sits within a range.
Compare extension types
The right footprint depends on the shape of your house, the garden you want to keep and the rooms you need.
Rear extension
£60,000 – £120,000+
Moves the back of the house into the garden to create a larger kitchen, dining or family space.
Rear extensions in London
Side-return extension
£55,000 – £100,000+
Uses the narrow passage beside many Victorian and Edwardian rear outriggers to widen the ground floor.
Side-return extensions explained
Wraparound extension
£80,000 – £160,000+
Combines rear and side-return space for a broader L-shaped ground-floor transformation.
Wraparound extensions explained
Double-storey extension
£100,000 – £190,000+
Adds space on two floors, often combining a larger ground floor with a bedroom or bathroom above.
Double-storey extensions explainedMini Extension Estimator
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Question 1 of 3 · Extension type
What your construction estimate covers
Your proposal confirms the exact scope. These headings help you compare early budgets on the same basis.
Usually within the construction scope
- Foundations, structure and structural steel
- Drainage work within the project
- Roof, glazing and external doors
- First and second fix plumbing and electrics
- Plastering and agreed base finishes
Allow for separately unless agreed
- Architectural, structural engineering, planning, Building Control and Party Wall fees
- Water-company applications and specialist surveys
- Kitchen units, worktops and appliances are excluded unless specifically agreed for your project. Kitchen installation can be included by prior agreement.
- Specialist joinery, premium finishes and landscaping
Planning and approvals
Some house extensions can proceed under permitted development if the proposal meets all relevant limits and conditions and those rights apply to the property. Flats and maisonettes have different rules. Conservation areas, listed buildings and local restrictions need particular checks; confirm the permissions and consents required for your property with the local planning authority.
Building Regulations apply separately, and Party Wall or drainage matters may also affect the sequence. Confirm the position for your property before committing to a programme.
Read the London planning permission guideIndicative build timelines
- Side return: 8–12 weeks
- Rear extension: 10–14 weeks
- Wraparound: 14–18 weeks
- Double-storey: 16–22 weeks
These are indicative on-site periods after approvals, not guaranteed programmes. Design, access, site conditions and changes can alter them.
Genuine project proof
Extension, renovation and loft conversion in Isleworth
This completed West London project combined a side extension, double-storey rear extension, loft conversion and full internal refurbishment.
Structural steel opened the ground floor into a larger kitchen, dining and living space, while the wider scheme added bedroom accommodation above.
View the Isleworth extension projectDoes an extension make sense for your home?
A well-designed extension can improve how a home works and may support its value, but there is no universal uplift. The result depends on the street, the quality of the design, the space retained outside and what local buyers value.
If you need a better kitchen and family space and want to stay where you are, extending may be more useful than moving. If the main need is another bedroom, compare the options before sacrificing garden space. Read more about how extension value varies.
Common Questions
House extension cost questions
Ready to make the numbers specific to your home?
Use the estimator for an immediate indicative range, or tell us about the property and what you want to change.