House Extension Cost London and Hertfordshire 2026
How much does a house extension cost in London? This is your complete guide to house extension prices in London and Hertfordshire for 2026, covering every type of extension with detailed cost breakdowns. LCCL Construction provides full design and build pricing with no hidden costs. LABC Award Winners 2024. Over 200 reviews rated 4.7 out of 5.
LABC Awards
Winners 2024
200+ Reviews
4.7 / 5 Rating
NFB Members
LABC Partners
How Much Does a House Extension Cost in London?
House extension costs in London vary depending on the type of extension, the size of the project and the level of specification. Here is a comprehensive breakdown of house extension costs in London and Hertfordshire for 2026:
Side return extension: £35,000 to £55,000.
Rear extension (3 to 4 metres): £35,000 to £55,000.
Rear extension (5 to 6 metres): £55,000 to £80,000.
Wraparound extension: £60,000 to £100,000.
Rear and side extension: £55,000 to £100,000.
Double-storey extension: £80,000 to £150,000.
Kitchen extension: £40,000 to £100,000.
Loft conversion and extension combined: £70,000 to £150,000.
All prices are for full design and build including architectural design, structural calculations, building regulations, construction, electrics, plumbing, plastering and decoration.
Please note: Every project is bespoke and individually designed to suit your property. All costs are indicative and subject to final architectural drawings, structural engineer calculations, finishing specification, project location, size and scope of works, any additional alterations, surveys and party wall agreements. A detailed written quote will be provided following your consultation.
1
What Affects the Cost of a House Extension?
Several factors influence the final cost of a house extension in London:
Size: Larger extensions cost more. The cost per square metre for a house extension in London is typically £2,000 to £3,000 for standard specification and £3,000 to £4,500 for high specification.
Structural work: Removing load-bearing walls, installing steel beams and underpinning foundations add to the cost.
Glazing: Bi-fold doors, sliding doors, roof lanterns and skylights are a significant cost element. High-quality aluminium bi-fold doors typically cost £3,000 to £8,000 depending on size.
Specification: Standard finishing versus premium materials, underfloor heating, bespoke joinery and high-end kitchen fitting all affect the budget.
Access: Properties with difficult access — narrow streets, basement levels, limited rear access — may cost more due to logistics.
Location: Properties in prime London areas tend to have higher costs. Properties in Barnet, Finchley, Hendon, Muswell Hill, Edgware and across Hertfordshire typically fall within the standard range.
Planning: Projects requiring full planning applications and those in conservation areas may incur additional design and application costs.
2
What Is Included in the Price?
LCCL Construction provides full design and build pricing that covers every stage: free consultation, measured building survey, architectural design, planning applications, building regulations, structural calculations, party wall agreements, all construction work, electrics, plumbing, plastering, decoration and building control sign-off. We also offer optional 10-year LABC warranties.
Our pricing is transparent with no hidden costs. We provide detailed written quotes before any work begins.
3
How to Get a Quote
There are three ways to get a quote from LCCL Construction:
Instant quote online: Visit lcclconstruction.co.uk/instant-quote for an indicative price in seconds.
Free consultation call: Book a call at lcclconstruction.co.uk/book-online to discuss your project in detail.
Call us: 020 8037 7332, Monday to Saturday 8am to 6pm.
We provide free no-obligation consultations and detailed written quotes for all house extension projects across London and Hertfordshire.
Frequently Asked Questions
What is the average cost of a house extension in London?
The average cost of a house extension in London is £50,000 to £70,000 for a standard single-storey rear extension with full design and build. Costs range from £35,000 for a small side return to £150,000 for a large combined loft and extension project.
What is the cost per square metre for a house extension in London?
The cost per square metre for a house extension in London is typically £2,000 to £3,000 for standard specification and £3,000 to £4,500 for high specification. These figures include construction, electrics, plumbing, plastering and decoration.
Are there any hidden costs with house extensions?
LCCL Construction provides transparent pricing with no hidden costs. Our quotes cover everything included in the design and build scope. Items that may be additional include kitchen units, specialist flooring, landscaping and any upgrades to the agreed specification.
Is a house extension cheaper than moving?
In most cases, yes. The costs of moving in London — stamp duty, estate agent fees, legal fees and the premium for a larger property — typically total £50,000 to £100,000 or more. A house extension can add equivalent space for less.
Do you offer payment plans or staged payments?
LCCL Construction uses a staged payment schedule tied to project milestones. You pay as the project progresses, not all upfront. Payment stages are agreed before work begins and set out in the contract.
How do I get a quote?
Get an instant quote at lcclconstruction.co.uk/instant-quote, book a free consultation at lcclconstruction.co.uk/book-online, or call us on 020 8037 7332.