One design-and-build contract
Architect, structural engineer, builder, one point of contact, one accountable price.
House Extensions · London
House extensions
in London,
designed, built and signed off.
Side-returns, rear and wrap-around extensions delivered watertight, insulated and finished to spec, with the architect, structural engineer and building control coordinated inside one fixed-price contract. Typical single-storey rear extension: 12-16 weeks on site.
5.0★ on Google · Constructionline Gold · Written quote back in the same week.
15 yrs
On the tools
£1M
Public liability
5.0★
Google rated
12 mo
Workmanship guarantee
Same wk
Written quote
Service overview
Extension design and build under one contract
What it is
A full house extension covers feasibility, architectural design, structural engineering, planning or permitted-development submission, building regulations, ground works, structure, roof, glazing, first fix, second fix, and internal finishing including kitchens and bathrooms where required. We manage the whole scope in-house.
Who it's for
Owners of London terraces, semis and townhouses who want to unlock a bigger kitchen-diner, an additional bedroom, a home office, or open-plan family living without moving house.
When you need it
The typical trigger is a growing family, a home-working set-up that no longer fits, or a purchase where the ground-floor footprint is holding the property back. Extensions are also the highest-return capital works you can do on a London property.
Why professional matters
An extension isn't a bigger version of a bathroom fit, it's a structural project with planning, building-control, party-wall and insurance-backed warranty implications. Getting the design and structural work right up front is what separates an extension that adds £250k of value from one that leaks in winter three.
The cost of getting it wrong
Why cheap extensions cost more in the long run
Extensions fail when the sequence is wrong or the design has been priced without properly checking the ground, the structure or the neighbouring party wall. Here's what that costs.
If ignored
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Party-wall disputes stall the build
Skip a proper Party Wall Award and a neighbour can freeze the job mid-dig. Delay costs on labour and hire are ruinous once you're past ground works.
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Undersized foundations
London clay is unforgiving. Cheap foundations sized without a soil review crack corners of new brickwork inside 24 months and can't be retrofitted cheaply.
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Cold-bridge and condensation failures
Poorly detailed junctions between old and new roofs produce cold bridges, black mould in bedroom ceilings and heat-loss you'll be paying for every winter.
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Building control sign-off refused
Work built off-spec doesn't pass building control. Uncertified work is a red flag on every future sale enquiry.
Common mistakes
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Starting on price alone
The cheapest tender almost always excludes something, usually structural steels, waste connections or an insured warranty. What arrives as an 'extra' 3 months in isn't an extra, it's an omission.
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No single point of accountability
When architect, structural engineer and builder are three separate companies, buck-passing is guaranteed. One design-and-build contract fixes it.
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Under-specifying glazing
Skimping on glazing g-values leaves an extension that overheats in July and haemorrhages heat in January. The uplift to proper thermal glazing is small; the running cost of getting it wrong is enormous.
How it works
A step-by-step system,
not a guess.
-
01
Step 1
Feasibility & free survey
Site visit, measure-up, review of what's achievable under permitted development or planning. Local surveys are free.
-
02
Step 2
Design & fixed quote
Architectural drawings, structural sign-off, and a detailed fixed-price quote back with you, normally inside 2-3 weeks for extensions.
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03
Step 3
Planning & Party Wall
Planning or PD application submitted, Party Wall Notices served, building control appointed. We handle the paperwork end-to-end.
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04
Step 4
Build phase
Ground works, structure, roof, glazing, first and second fix, weekly written progress updates from the founder himself.
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05
Step 5
Sign-off & guarantee
Building control completion certificate, snag-free handover, and a 12-month workmanship guarantee in writing.
What you actually get
Concrete outcomes,
not adjectives.
Correct foundations, once
Foundations designed against actual soil conditions, not a guess. No cracked corners two winters in.
Thermally-detailed junctions
Old-to-new roof and wall junctions detailed against condensation risk. No mould, no cold bridges.
Building control handled
Planning, PD, Party Wall Notices, building regs and completion certificate, arranged as part of the job.
PRINCE2 project management
Programme managed against milestones with weekly written client updates.
12-month workmanship guarantee
Written guarantee on top of any manufacturer warranties on windows, roofing and glazing.
Materials & methods
Extension types, materials & structural methods
Every London extension is different. Terrace footprints, boundary constraints, and planning history all shape what's possible. Here's the range we deliver.
Materials we work with
- Traditional cavity-wall brick and block with insulated cavities
- Timber-frame and SIPS panel construction for faster shell erection
- Steel-frame structural openings for open-plan interiors
- Warm-roof flat roofs with EPDM, single-ply or GRP finishes
- Aluminium sliding, bi-fold and lantern rooflight glazing
- Solid-timber and engineered flooring, cast-in-situ concrete floors, polished screed
- Underfloor heating manifolds coordinated with new boiler capacity
Methods & standards
- Trial holes and (where needed) engineer-designed foundations against soil conditions
- Steel schedule prepared by an independent structural engineer
- Party Wall Awards where the extension abuts or approaches a shared wall
- Building control inspections at foundation, DPC, superstructure and completion
- Thermally detailed junctions to eliminate cold bridging at old-to-new interfaces
Variations of this service
Single-storey rear extension
The most common London extension, 3-6m deep off the back of the house, usually forming an open-plan kitchen-diner.
Side-return infill
Filling in the side alley on Victorian and Edwardian terraces to widen the kitchen. Requires party-wall handling on both sides.
Wrap-around extension
Combining rear and side-return in a single L-shape to maximise ground-floor space.
Double-storey rear extension
Adding a bedroom or bathroom above a new kitchen extension. Requires more careful structural work into existing floor levels.
Garden-room / annexe builds
Detached garden studios and annexes for home working, gyms or guest accommodation.
Property types & settings
We build extensions on Victorian and Edwardian terraces, semis and detached houses across North and West London. Commercial extensions, small retail and hospitality, are handled under our commercial fit-out service.
Every extension is quoted on a fixed-price basis after a feasibility survey. Ground conditions, glazing spec, roof form and internal finish drive the number, so we never quote from postcodes alone. You'll have an itemised written quote back inside 2-3 weeks.
A single-storey rear extension typically runs 12-16 weeks on site once ground works start. Design, planning and Party Wall usually add 8-12 weeks before that. The full programme is agreed in writing before we mobilise.
Many rear and side-return extensions in London fall under permitted development, but PD rights are restricted in conservation areas and on flats. We check this at the feasibility stage and confirm whether a full planning application, PD prior-approval or a Lawful Development Certificate is needed.
If your extension abuts, cuts into or excavates near a shared wall, the Party Wall etc. Act 1996 requires you to serve notice on neighbours. We arrange the notices and, where a surveyor is appointed, coordinate the Award as part of the job.
Yes. Architectural drawings and structural engineer sign-off are handled in-house through our design partners. You deal with one contact for the whole project.
Every extension carries our 12-month workmanship guarantee in writing. Manufacturer warranties on glazing, roofing membranes and boilers sit on top of that. For mortgage or resale purposes we can also arrange a structural warranty on request.
Yes, in most cases. We phase the works so the existing kitchen or bathroom is only out of use for the second-fix stage, and we agree noise / access hours with you up front.
We build throughout North and West London, including St John's Wood, Paddington, Kensington, Bayswater, Regents Park, Hampstead, Hammersmith, Chiswick and Ealing Broadway.
In prime North and West London, a well-detailed extension is one of the highest-return capital works you can do, typically returning more than its build cost at resale. Specific uplift is best confirmed with a local estate agent against comparable sold prices on your street.
Book your free survey
Ready to price your house extensions
the honest way?
One site visit. One fixed-price written quote back the same week. No pressure, no hard sell, just the number and the plan to deliver it.
- Free local survey
- Written quote the same week
- Fixed-price, staged payments
- 12-month workmanship guarantee
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