2026 UK cost guide
How much does a house extension cost in the UK?
A useful first budget needs more than a price per square metre. Structure, access, kitchen work, glazing and how much of the existing house changes can move the total quickly.
Illustrative UK starting range
£65,000–£132,000a 30 m² rear extension across three contrasting scenarios, including VAT where charged.
This is a deliberately wide scenario range from Proper Job pricing model v14, not a UK average, quotation or promise of local availability. Your useful range should use the actual property, postcode, size, scope, access and choices.
Why the range is wide
The same project label can describe a very different job
A quick rear extension to a terraced rental, kept simple with practical finishes and little internal change, is a different job from a central London family-home extension with restricted access, structural alterations, bespoke glazing and premium detailing. Both may be called a rear extension, but they should not share one headline price.
North West
Straightforward and practical
£65,000–£85,000A simple terraced rental extension with practical finishes, limited internal alteration and no premium detailing.
South East
Typical family-home scope
£76,000–£99,000A family-home extension with a good domestic finish and a balanced allowance for the main knock-on work.
London
Premium and more complex
£101,000–£132,000A central London family-home project with premium finishes, broader internal changes and more demanding logistics.
How Proper Job turns the broad range into something useful
Guide Price uses the actual postcode, size, scope, finish, site conditions and likely extras to create a more relevant early range.
Detailed Estimate then uses architectural drawings to measure and itemise the work, while keeping specifications, site conditions and client choices that still need confirming visible.
What moves the price
- Single-storey, two-storey, side-return or wraparound form
- Ground conditions, drainage moves and structural steel
- Kitchen, utility and knock-through work inside the existing house
- Glazing, rooflights, doors and finish level
- Restricted access, parking, neighbours and working-hour limits
What this example allows for
- A ballpark-stage allowance for a rear extension shell and standard domestic finish
- Regional pricing pressure across three contrasting UK examples
- A contractor margin and a wider range for early unknowns
- VAT added for the homeowner-facing example where it is charged
Before you ask builders for quotes
- Confirm the extension footprint and whether the kitchen is part of the works
- Identify drainage, party-wall, access and planning constraints
- Separate supply items such as the kitchen, glazing and flooring
- Ask builders to price the same drawings, specification and exclusions
Questions homeowners ask
Is this a quotation?
No. It is an early budget example from Proper Job’s current pricing model. A builder still needs drawings, site information and a defined specification for a firm quotation.
Does the size alone decide the cost?
No. Size is only one driver. Structure, existing-house alterations, access, finish, services and supply items can matter just as much.
Should I include VAT in my budget?
Usually, yes. The example shown here includes 20% VAT, but the final treatment depends on the contractor and the work.
Use your project, not the example
Add the real size, finish, logistics and likely extras. Your first Proper Job guide is free.
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Pricing example checked 17 July 2026.