How Much Does Home Extension Cost?

Costs for single and double-storey rear, side, and wraparound extensions across London — design, planning, build, fit-out.

Budget

£32,500

Average

£66,000

Premium

£136,500

Home Extension Price Breakdown

Item	Budget	Mid-Range	Premium	Notes
Architecture & planning	£3,000	£6,000	£12,000	-
Structural engineer	£1,500	£2,500	£4,500	-
Foundations & groundworks	£8,000	£14,000	£28,000	-
Shell construction (per sqm)	£2,200 /per sqm	£3,000 /per sqm	£4,500 /per sqm	-
Glazing (bifolds/sliders)	£4,000	£12,000	£30,000	-
Roofing & insulation	£4,500	£8,000	£16,000	-
Electrical & plumbing	£3,500	£6,500	£12,000	-
Plastering & decoration	£2,500	£5,000	£9,000	-
Flooring	£1,500	£4,000	£9,000	-
Project management	£4,000	£8,000	£16,000	-
Total (Fixed Items)	£32,500	£66,000	£136,500

What Affects Home Extension Cost?

high impact

Extension size (sqm)

Cost typically £2,200-£4,500 per sqm for the shell, more for fit-out.

high impact

Storey count

Double-storey is more cost-efficient per sqm than single-storey.

high impact

Glazing extent

Large bifolds, sliding doors, and rooflights add £8-30k.

medium impact

Planning route

Permitted development is faster; full planning needed for larger or conservation builds.

high impact

Foundations

Mass-fill vs piled vs raft depending on ground and trees.

high impact

Specification of fit-out

Mid-range vs prime kitchen, flooring, joinery.

Home Extension Cost by Area

Prices vary by location. Select an area for specific local pricing.

Hampstead

Conservation area, prime spec.

From £42,250

✓ Included in Our Quotes

✓Architectural design and Building Control package
✓Structural engineering coordination
✓Planning application submission and management
✓Party Wall coordination
✓Full build to wind-and-watertight
✓Fit-out and finish to agreed specification

✗ Not Included (May Be Extra)

✗Planning consultancy fees (separate)
✗Party Wall surveyor fees
✗Tree surveys and arboricultural reports
✗Underpinning of neighbouring properties
✗Landscaping and external works
✗Furniture and styling

💡 Money-Saving Tips

Stay within Permitted Development limits where possible — saves 8-12 weeks vs full planning.

Single-storey full-width rear extensions often produce the best value-per-sqm.

Use proprietary roof glazing rather than bespoke structural glass for cost-effective light.

Specify the kitchen and flooring as part of the contract to lock pricing early.

Combine with internal reconfiguration to share scaffolding and crew mobilisation.

Home Extension Cost FAQs

Find answers to common questions about our services.

Single-storey rear: 12-16 weeks on site. Double-storey or wraparound: 18-26 weeks. Add 8-16 weeks for design, planning and pre-construction.

Many rear extensions fall under Permitted Development, but conservation areas, listed buildings, large extensions, and side extensions usually need full planning. We assess your case at the design stage.

A well-designed extension typically adds 15-25% to property value in prime North London, with the largest uplift on family homes converted to open-plan living.