Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Loft conversions, house extensions, renovations, basements and new builds across London and Hertfordshire.
Services
Call 020 8037 7332 or get an instant estimate online.
Single-storey extensions · London & Hertfordshire
Ground floor extension London: rear, side return or wraparound — which one, and what it costs
By Anderson & the LCCL Construction Team
Finchley N3 · Design & build, LABC award winners 2024 and 2026
Every single-storey extension is one of three shapes: out the back, into the side return, or both. Which one suits your house decides the cost, the planning route and how much of the garden you keep. This page compares the three side by side with the 2026 numbers, then points you to the detailed page for the shape you need.
Quick answer
£42,000 – £153,600 inc. VAT (£35,000 – £128,000 + VAT) for a single-storey extension, design and build inclusive — rear £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT), side return £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT), wraparound £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT).
Rear and side return extensions are usually permitted development; a wraparound usually needs a planning application.
10–18 weeks on site depending on the shape; 8–16 weeks of design and approvals before that.
A free 30-minute phone call with our team, no obligation.
Guide price
£42,000 – £153,600 inc. VAT (£35,000 – £128,000 + VAT)
Typical build
10–18 weeks on site
Guarantee
12-month workmanship guarantee; 10-year LABC structural warranty
Awards
LABC 2024 & 2026 winners
LABC Building Excellence Award 2024
Best Residential Extension in London — Bohun Grove, East Barnet EN4: rear extension, hip-to-gable loft conversion and whole-house renovation
LABC Building Excellence Awards 2026
London Regional Winner, Best Conversion or Alteration — Weech Road, Hampstead NW6: penthouse loft conversion and full renovation
One contract
Architecture, structural engineering, planning, construction and project management — all under one contract
Guaranteed & insured
12-month workmanship guarantee; 10-year LABC structural warranty
What a ground floor extension from LCCL includes
The same design and build package whichever shape you choose.
Measured survey of the house and garden
Architectural design and drawings, with revisions until you're happy
Planning application or Lawful Development Certificate, prepared and submitted for you
Building regulations drawings and structural calculations by our chartered engineer
Party wall notices served on your behalf (£300 each, at cost)
Foundations, drainage and any build-over agreement with Thames Water
Structure, roof, rooflights, doors and windows to a weather-tight shell
Plaster finish, first-fix electrics and plumbing, underfloor heating where specified
Fitting of the kitchen, flooring and second-fix items you supply
LABC inspections and completion certificate
A dedicated project manager and a weekly progress update
12-month workmanship guarantee; 10-year LABC structural warranty
How much does a ground floor extension cost in London in 2026?
The three shapes compared. Every project is priced from your postcode and house type.
Shape
What it gives you
Guide range
Rear extension 3–6 m deep
Depth — a kitchen-diner and garden doors across the back
£42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT)
Side return infill
Width — a galley kitchen becomes full width, garden depth kept
£42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT)
Wraparound side + rear
Both — an L-shaped kitchen, dining and living room
£72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT)
Also consider
Guide range
On site
Kitchen fit-out on top of the build
Kitchen supplied and fitted — priced by size and specification on every proposal
£9,000 – £87,360 inc. VAT (£7,500 – £72,800 + VAT)
Within the build
Two storey extension
A bedroom or bathroom above the new kitchen; usually a planning application
£90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT)
16–24 wks
Loft conversion instead of, or as well as
Bedroom in the roof, usually permitted development
£32,400 – £148,800 inc. VAT (£27,000 – £124,000 + VAT)
4–16 wks
What the price includes: survey, architectural drawings, lawful development certificate or planning, building-regulations drawings, structural calculations, construction to plaster finish with first-fix electrics and plumbing, LABC sign-off and guarantees. On top: the kitchen, flooring and second-fix items you choose. The figure on your itemised estimate is the figure you pay — nothing is added afterwards. Postcode dependent — the instant estimator adjusts the range for your area in thirty seconds, and a detailed itemised estimate follows one survey.
What moves the price: the footprint; the amount of glazing; the steel where the back or outrigger wall comes out; drainage and any Thames Water build-over agreement; ground conditions and tree roots; and the finish inside. Inner and Central London (Camden, Islington, Hackney, Wandsworth, Hammersmith, Westminster, Kensington & Chelsea, the City) cost more than outer London and Hertfordshire a little less — the instant estimate applies your postcode. These are estimated ranges — every home is surveyed and costed individually.
Which shape suits which house?
Victorian or Edwardian terrace
The side return is the usual first move — it widens the kitchen for the least money and no planning application. Add depth beyond the outrigger and it becomes a wraparound, which normally needs planning. A plain rear extension to the outrigger is the third option where the side return is too narrow to be worth it.
1930s semi
A full-width rear extension of 3–4 m across the back is the standard answer: permitted development to 3 m, prior approval to 6 m. The side passage is sometimes filled too for a utility, keeping a 1 m access.
Detached house
Rear extension almost every time: 4 m under permitted development, 8 m by prior approval, so a planning application is rarely needed. The limits that bite are height near the boundary and the half-garden rule.
Planning
Do you need planning permission for a ground floor extension?
Usually not for a rear or side return extension. The shape decides the route.
Shape
Usual route
Time
What we do
Rear to 3 m (4 m detached)
Permitted development
No application
Lawful Development Certificate, ~8 weeks, included
Rear to 6 m (8 m detached)
Prior approval (larger home extension)
42 days
Neighbour notification submission prepared by us
Side return within PD limits
Permitted development
No application
Lawful Development Certificate included
Wraparound, flats, conservation areas
Full planning
8 weeks
Drawings, design statement and application by our team
Building regulations & party walls
The other two approvals
Every extension needs building-regulations approval whether or not it needs planning: foundations, structure, insulation, glazing area, drainage and fire. We do this through LABC with full-plans drawings and our own structural calculations, so the inspector is checking a design he has already approved, not improvising on site.
If the extension is on or near the boundary of a semi or terrace, the Party Wall Act applies. Notices go out at least two months before we start; most neighbours consent, and where a surveyor is appointed we manage it.
Permitted development is removed on flats, in some conservation areas, under Article 4 directions and on houses where an earlier consent took the rights away. We check your address before the first drawing and obtain a Lawful Development Certificate as part of the design stage — it is the only document that proves the extension was lawful when you sell.
Permitted development rights for house extensions · House extension planning permission See our permitted development projects page for every loft and extension you can build without a planning application, with from-prices at economy specification. Not sure whether your project needs a planning application? Check if you need planning permission
Recent single-storey extension projects
Bohun Grove, East Barnet EN4 — rear extension, hip-to-gable loft and whole-house renovation
LABC 2024 Best Residential Extension in London
Semi-detached family home One programme loft + extension + renovation
A total renovation of a family semi: a rear extension opening into a full-width kitchen and dining space with floor-to-ceiling glazing and skylights, a hip-to-gable loft conversion with a rear dormer, two Lusso Stone bathrooms, enlarged bedrooms, new windows throughout, a regulated outbuilding and landscaping.
Because the loft and extension ran under one contract, the steelwork for the open-plan ground floor and the loft floor was designed together and lifted in on the same day — one crane hire, one scaffold, one building-control file.
See the Bohun Grove project · All projects
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ANDERSON · FOUNDER, LCCL CONSTRUCTION
Anderson's advice: book the design stage in summer, build in autumn
August is our slowest month for project starts — most families delay until the schools go back. That makes it the best time to get the survey, drawings and approvals done: you go through the council queue while everyone else is on holiday and start on site in September or October with the paperwork finished.
Approvals are the part of the programme you cannot compress. Design and planning typically take 8–16 weeks; leave them to the last minute and the build slips into the following year.
How a ground floor extension runs with LCCL
From the first call to the completion certificate. Design, planning and building regulations typically take 8–16 weeks before work starts.
WEEK 0
Free consultation call
A 30-minute phone call with our team about the house, what you want from the space and a realistic budget. Your instant estimate is the starting point.
WEEKS 1–4
Survey & design
Measured survey, architectural drawings and your detailed itemised estimate — design, planning, structure, construction and warranty priced line by line.
WEEKS 4–12
Approvals
Lawful Development Certificate or planning application, building-regulations drawings, structural calculations, party wall notices. Nothing starts on site until it is signed off.
BUILD
On site
10–18 weeks on site for a single-storey extension, depending on the shape. Weekly updates from your project manager, one point of contact throughout.
HANDOVER
Sign-off
Snagging, LABC final inspection and completion certificate, guarantees in writing. 10-year LABC structural warranty.
“LCCL Construction was the right company to help with my loft conversion. I heard of other people's challenging experiences with building works so I was very careful which company I chose. LCCL Constructions was professional, trustworthy and worked to the…”
KashImaging · Trustpilot
“Contracted lccl construction to design and build hip to gable loft conversion, after much research I found Lccl construction to be the most efficient and reliable company to deal with, the initial design phases started immediately their architects attended…”
Behar · Trustpilot
“2ND project with LCCL construction wraparound house extension. Completed full design and build process to our home in Finchley north London. Previously they have design and build our loft conversion 4 years on and still it is in excellent condition.…”
Anthony · Trustpilot
Ground floor extension questions we get asked most
£42,000 – £153,600 inc. VAT (£35,000 – £128,000 + VAT) in 2026, design and build inclusive, depending on the shape: a rear extension £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT), a side return £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT), a wraparound £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT). The kitchen fit-out is priced on top. The instant estimator gives you a figure for your postcode in thirty seconds.
Ask what the space is for. Width in the existing kitchen: side return. A dining room and doors to the garden: rear. Both, in one open-plan room: wraparound. The house type narrows it further — terraces have side returns, semis and detached houses usually go straight out the back. The consultation call settles it in half an hour.
Usually not. Rear extensions to 3 m (4 m detached) and side returns within the limits are permitted development; rear extensions to 6 m (8 m detached) go through prior approval. Wraparounds, flats and conservation-area houses need a full application. We check your address first.
Ten to fourteen weeks on site for a rear or side return extension, fourteen to eighteen for a wraparound, plus 8–16 weeks of design and approvals before that.
A 3 m rear extension or a plain side return infill, both from £42,000 inc. VAT (£35,000 + VAT), both usually without a planning application. Keep the glazing modest and the roof flat with rooflights and the price stays at the bottom of the range.
Yes, and it costs less than doing them separately because the scaffold, structural design and party wall process are shared. See our loft + extension page.
A 3 m rear extension takes 3 m of garden depth; a side return takes none. Permitted development also caps the extension and any outbuildings at half the original garden area. On a short terrace garden that is often the deciding factor in favour of a side return.
An open-plan kitchen-diner is the improvement most London buyers pay for. Our house-extension value guide sets out what the data shows by area. We are not valuers, so treat any figure as indicative and talk to a local agent before you commit.
Where we build ground floor extensions
From Finchley N3 we cover North London, North-West London, Central London, South-West and West London, and Hertfordshire — and we also work across the rest of London, Buckinghamshire, Surrey, Kent and Essex. Recent single-storey extensions: East Barnet EN4, Finchley N3, Putney SW15 and Highbury N5.