House extensions are one of the biggest investments homeowners make. In Sevenoaks, costs tend to be higher than the UK average due to demand, specification expectations and property values.
Average House Extension Costs in Sevenoaks
As a general guide for 2026:
- Single-storey extension: £2,200 – £3,000 per m²
- Two-storey extension: £2,000 – £2,700 per m²
For a typical 30m² rear extension, this equates to £66,000 – £90,000+.
What Affects the Final Cost?
Design and Complexity
Large glazing panels, steelwork and flat roofs increase build costs.
Ground Conditions
Poor soil or drainage can require deeper foundations and additional groundwork.
Specification and Finishes
Kitchens, bathrooms and bespoke joinery often exceed structural costs.
Professional Fees
Architects, engineers and planning fees typically add 10–15% to the total budget.
Hidden Costs to Budget For
- Party wall surveyor fees
- Utility upgrades
- Temporary accommodation
- Landscaping after completion
Is an Extension Worth It in Sevenoaks?
In many cases, extending is more cost-effective than moving when stamp duty, legal fees and agent costs are considered.
Join the Struxi waitlist to plan your extension with confidence.
Sources
- Homebuilding & Renovating – Extension costs: https://www.homebuilding.co.uk
- Checkatrade – House extension pricing: https://www.checkatrade.com
- RICS – Construction cost insights: https://www.rics.org