Already designed with us?
Carry on to the Build Phase. Same team, single contract, no re-tender.
Book a build consultation
Build
Phase
A managed London extension build. From our drawings, or from yours.
A managed London extension build. From our drawings, or from yours.
How the Build Phase works
The Build Phase gives you a single contract, a dedicated Build Manager on site, ten-stage payment in arrears, and a 3-year structural guarantee plus 2 years' defects liability. A typical London single-storey extension takes twelve to twenty weeks on site. We build from any architect's drawings: ours, yours or a third party's.
Designed elsewhere?
Send us the drawings. We'll quote a fixed-price build inside ten working days.
Get a build quoteHow much does a
London extension cost?
Typical cost per m²:
£2,800–£5,500+ per m² for an architect-designed extension on a London Victorian or Edwardian terrace (May 2026 figures).
For a typical 20 m² single-storey rear extension
that is £56,000–£110,000 build cost, before kitchen fit-out.
Standard spec, what most projects deliver:
brick matched to existing Victorian or Edwardian stock, bi-fold or sliding doors, integrated lighting, mid-range kitchen fit-out, full Building Regs compliance.
Higher spec adds:
architectural glazing, underfloor heating, specialist tiling, made-to-measure joinery.
What moves the price:
the borough (West London typically +10–15% on East), conservation status, ground conditions, access constraints (Victorian terraces with no side access add cost), the spec of the kitchen.
From our own projects:
Real build costs, floor areas and time on site for finished Build Team projects are in our case studies, listed by project and borough.
How we run a build, and what
a design-only service doesn't do
Build Team Build Phase
A design-only service
Who oversees payment certifications
Your dedicated Build Manager
You manage the contractor
The contract
We put the contracts in place
You contract direct with the builder
Payment terms
Ten stage payment plan, paid in arrears after works start
Whatever the builder asks for
Vetting
£2m public liability, insured, background-checked
Your job
Site meetings
Typically weekly, with your Build Manager
None as standard
Snagging
Checked and signed off by Build Team
You own it
Structural guarantee
Three years from Build Team, plus 2 years' defects liability
Whatever the builder offers
Points of contact
Build Manager & Foreman
You and the builder
The ten stages of a
London extension build
01
Site setup & strip out
1 week
02
Foundations are dug and poured
2 weeks
03
New cavity walls
1 week
04
Structural steels installed
1–2 weeks
05
Roof construction
2 weeks
06
Drainage and sub floor
1 week
07
Insulated screed floor
2 weeks
08
Timber partition and plaster skimming
2 weeks
09
Practical Completion
1 week
10
Snagging
1 week
What can go wrong on a London
build, and how we handle it
"What if the build goes over budget?"
The contract is fixed-price against an agreed specification. Variations only come from you asking for a change in scope, or from genuine site discoveries (rot, ground conditions, drains) that cannot be identified without invasive works. A contingency of around 10% is standard practice for any London extension and we recommend building that into your budget at the outset.
"What if my builder disappears mid-project?"
As part of our service, we will replace the Principal Contractor with another from our vetted pool in the unlikely event they can't complete the project after they've started.
"What if Building Control sign-off gets dragged out?"
The Build Manager owns the Building Control diary from day one and books inspections in advance of each stage. Local authority Building Control fees for a typical London extension are generally between £900–£1,500. Where instructed to do so, the Build Manager will liaise with Building Control and the Principal Contractor to facilitate the sign off process upon completion.
"What if I can't live in the house during the build?"
On most single-storey ground floor extensions you can stay in the house. The kitchen comes out during the strip-out phase and we can set up a temporary one for the duration of the works. For loft conversions, most clients remain at the property for the duration of the works. For full-house refurbishments they tend to move out for some or all of the works. We produce a project programme at the outset which will indicate the most disruptive elements of the schedule.
Our Build Managers
Your Build Manager visits the site every week, is your one point of contact, and certifies each stage before you pay for it.
Gustavo Cilumbriello
Build Director
Sandra Ditchfield-Ortiz
Build Manager
Sean Kember
Build Manager
Adnan Ali
Build Manager
Recent Builds
Build Phase FAQ
How much does it cost to build a single-storey extension in London?
A single-storey ground floor extension project costs roughly £80,000 – £150,000 inclusive of VAT in 2026.
How long does a London extension build take?
The construction of the shell & core takes approximately 14-16 weeks. We recommend allowing an additional 2-4 weeks for the finishing schedule to be undertaken.
Will you build from another architect's drawings?
Yes, we can build from another architect's drawing set. We will also require structural engineering calculations and building regulation drawings and can produce these via our in-house design team if you require them.
What's the difference between Design & Build and using an architect plus a builder?
Design and build gives you one point of contact from first drawing to handover. The tender happens more quickly, or not at all if you ask us to fix the build costs before the design phase starts. If you appoint a separate Architect, you will need to pay them to tender the project to contractors or undertake this part of the process yourselves.
What does the Build Team structural guarantee cover?
The structural guarantee covers the works against major structural defects for 3 years after completion. A 2-year defects liability period runs alongside it.
How does payment in arrears work in practice?
Upon completion of core milestones identified within the project planner, your Build Manager within 48 hours of notification from the contractor will raise in part or in full the payment certification for that stage. Payment to the Principal Contractor is due upon receipt of this certification.
What if my architect has specified something unbuildable?
Before you sign a build contract with us, our Build Director reviews your architect's drawings to check they can be built. If something is wrong or missing from the drawing package, we will tell you so that you can go back to your Architect to make the required amendment ahead of starting the build.
Do I still need a party wall agreement?
Usually, yes. You must serve a Party Wall Notice if you build on or against the party wall or boundary, or dig foundations within 3m of a neighbour's building (6 metres in some cases). Most side returns and many rear extensions need one, and our party wall team can serve it for you.
What happens to my Building Control sign-off?
Building Control will need to be appointed prior to works commencing on site which takes up to 10 days; they will inspect the construction drawings and make regular planned site visits and issue the final build certificate. You can appoint Building Control yourself, or you can appoint Build Team to administer this process on your behalf for an additional fee.
Two ways to start.
