Common benchmark
£1,800-£3,000
Published standard extension build-cost range per m2.
Home extension guide
How Much Does a House Extension Cost?
Published UK guides commonly place standard extension build costs around £1,800 to £3,000 per square metre, but the real figure depends on size, structure, site conditions, specification and what is included in the quote.
Budget planning
Use benchmark numbers, then define the real scope.
Planning context
£548
Typical England householder planning application fee.
Prior approval
£249
Current larger rear extension prior-approval context.
Sources reviewed
11
Current UK cost, planning and process references.
Fast answer
A useful budget starts with size, then gets corrected by scope.
These examples are broad UK benchmarks, not fixed Ensign prices. They are useful for early planning and for spotting which details still need to be defined.
20 m2 extension
£40,000 to £56,000
A modest single-storey benchmark where specification can still move the final quote.
30 m2 extension
£60,000 to £84,000
A common mid-sized rear or side extension example used by published UK cost guides.
50 m2 extension
£100,000 to £140,000
A larger extension where internal works, glazing and finishes become especially important.
Cost drivers
Two extensions with the same floor area can price very differently.
- Size, shape and number of storeys.
- Groundworks, drainage, foundations and structural steelwork.
- Roof design, insulation, glazing and external openings.
- Kitchen, bathroom, utility or service relocations.
- Finish level, fixtures, fittings and client-supplied items.
- Professional fees, statutory fees, VAT and contingency.
Budget breakdown
Where the money usually goes.
A quote is easier to compare when it is broken into the real parts of the job.
Design and early decisions
Drawings, surveys, structural calculations, planning checks and specification decisions shape the budget before construction begins.
Site preparation and structure
Groundworks, foundations, drainage, steelwork and the shell are major cost areas, especially where access or existing buildings add complexity.
Weatherproofing and services
Roofing, windows, doors, insulation, electrics, plumbing and heating choices can move the project well beyond a simple shell cost.
Finishes and handover
Plastering, flooring, kitchens, bathrooms, decoration and final detailing are where two similar extensions can finish at very different totals.
Extension type
The kind of extension changes the conversation.
Single-storey rear or side extensions
Usually the simplest extension type to compare, but structure, openings, roof design and internal remodelling still matter.
Two-storey extensions
A two-storey extension normally costs more overall, but some fixed costs are shared across the project.
Extension plus renovation
Many real projects include knock-throughs, kitchens, bathrooms, landscaping or wider renovation work that should be priced as one complete scope.
Before you ask for a quote
Move from a rough number to a clear brief.
Ensign can have a better first conversation when the brief already describes the project, location, drawings, timing and known budget expectations.
Related projects
Cost makes more sense when you can see the type of work.
Rear Extension and Renovation in Lowton
A useful example of an extension combined with wider renovation work and project coordination.
Modern Rear and Side Extensions in Whittle Hall
A rear and side extension example for comparing added space, structure and finish expectations.
Renovation and Extension in Padgate
A broader renovation-plus-extension project showing why scope clarity matters before pricing.
Sources and caveats
The numbers are benchmarks, not a fixed quote.
The guide uses current UK benchmark sources and official fee context so the figures are useful without pretending every project is the same.
Checkatrade
House Extension: Cost Breakdown 2026
General UK benchmark ranges, common project sizes and homeowner cost drivers.
HomeOwners Alliance
House extension costs: Breakdown by size & type
Independent homeowner-facing summary of UK 2026 extension cost benchmarks and factors.
Resi
House extension cost: how to budget for your project
Range breadth, outside-London vs London comparison and exclusion caveats.
Planning Portal
How much does a planning application cost?
Current statutory planning-fee context for a typical England householder application.
GOV.UK
Planning fees: annual indexation from 1 April 2026
Official England fee schedule for householder applications and prior approval.
Checkatrade
How Much Do Building Regs Cost in the UK in 2026?
Indicative building-control approval and inspection cost ranges.
FAQs
House extension cost questions.
Can Ensign price an extension from an online cost guide?
A guide can help you understand likely budget areas, but a proper quote needs the project brief, drawings or scope, site conditions, specification and any planning or building-control requirements.
Is a single-storey extension always cheaper than a two-storey extension?
Not always in simple per-square-metre terms. A two-storey extension usually costs more overall, but some fixed costs are shared across the project.
Should I include VAT, kitchens and bathrooms in my budget?
Yes, if those items are part of the project. Published benchmark ranges often exclude some fit-out items or VAT, so confirm exactly what is included before comparing quotes.
Will I need planning permission?
That depends on the property, extension size, location, boundaries and previous alterations. Some projects may fall under permitted development, while others need planning approval or prior approval.
Ready to talk through a real project?