House Extensions London 2026: Complete Guide by LABC Award Winners
Updated: 7 days ago
By Anderson & the LCCL Construction Team | Finchley N3
On our projects and local sold prices, a well-planned project of this kind usually adds more to the value of the home than it costs to build — see our guide on how much value an extension adds. As LABC Building Excellence Award Winners 2024 for Best Residential Extension in London, LCCL Construction has delivered hundreds of house extensions across London and Hertfordshire over the past 20 years. This guide sets out everything you need to know about house extensions in London in 2026 — costs, types, planning, timelines and how to choose the right company.
Types of House Extension in London 2026
Six main house extension types in London: rear extensions (£42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT)), side return extensions (£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)), wraparound extensions (£72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)), double storey extensions (£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)), kitchen extensions and basement conversions. The right type depends on your property, garden, plot access and budget.
A Real LCCL Kitchen Extension Project: Mill Hill NW7
One of our recent projects at Guardhouse Way in Mill Hill NW7 (Millbrook Park) shows what a well-designed extension can deliver. The purpose was to create a large modern kitchen and dining area — a social space where friends and family could cook, socialise, do homework, relax and work from home. In line with current trends, a separate utility room was planned to remove laundry from the kitchen. The result: significantly reduced noise levels in the main kitchen and substantially more cupboard space where it mattered.
Anderson's Advice: The Costs Clients Forget
From 20 years of running extension projects across London, the single biggest budget surprise for clients is structural steelwork. Clients budget carefully for kitchen units, appliances, worktops and finishes — but often forget the structural steelwork required to open up existing ground floor walls and support new floors above. On a typical Victorian terrace opening up the kitchen to the extension, expect £4,800 – £19,200 inc. VAT (£4,000 – £16,000 + VAT) for the load-bearing opening through the external wall — steel, padstones, installation and making good — depending on its width. Factor this in from day one and you avoid the mid-project shock.
House Extension Planning Permission in London
Some single storey rear extensions fall within permitted development. Most double storey, wraparound, side return and extensions in conservation areas require full planning permission. Planning experience varies significantly by borough — Wandsworth is much more helpful on pre-application than Islington in our experience. LCCL Construction handles all planning applications. See our full planning permission guide.
House Extension Costs London 2026 — Complete Range
Total 2026 range: £35,000 for small rear extensions to £185,000+ for large double storey wraparounds in Central London. Average project: £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT). See our full home extension cost guide for detailed breakdown by extension type.
What Our Clients Say
"LCCL Constructions was professional, trustworthy and worked to the highest standard. The process was smooth and I'm very happy with the result - it has transformed the quality of my home." — KashImaging, Trustpilot
"We have used Lccl in the past for our rear house extension and have come back to instruct Lccl for our loft conversion too to our house in North London. As before we are very happy with the services from Lccl and we highly recommend their design and construction services for both home extension or loft conversion including both design and build services." — Mia M, Google Reviews
Why LCCL Construction?
Finchley N3 based, covering all of London and Hertfordshire. Over 20 years of experience. 200+ verified reviews rated 4.7/5. LABC Building Excellence Award Winners 2024. LABC Registered Partners. National Federation of Builders members. One team, one contract, one point of contact — from first sketch to handover.
Frequently Asked Questions
How much does a house extension cost in London?
From £42,000 inc. VAT (£35,000 + VAT) for a small rear extension to £198,000 inc. VAT (£165,000 + VAT) for a large double storey. Average project £90,000 – £114,000 inc. VAT (£75,000 – £95,000 + VAT).
Do I need planning permission for a house extension in London?
Some rear extensions fall within permitted development; most other types require full planning permission.
To book a free consultation with LCCL Construction call 020 8037 7332 or get an instant quote online.
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