Did your design 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.
Build Phase
A managed London extension build. From our drawings, or from yours.
SUMMARY
Our Build Phase runs a single contract with you, a dedicated Build Manager on site, ten-stage payment in arrears, and a three-year structural warranty. A typical London single-storey extension build runs 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?
Headline range:
£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.
Premium spec adds:
architectural glazing, underfloor heating, specialist tiling, bespoke 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 project data:
[Postcode-level averages — TBC with Dan from BuildTeam project data]
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 warranty
Three years, provided by Build Team
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 for three months?"
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 – and 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
Weekly site visits. Dedicated point of contact. Owns contract administration and payment certifications.
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?
Working with a design and build company means you have a single point of contact from start to finish. It also means the tender process happens more quickly — or dispensed with entirely if you ask us to fix the build costs upfront before the design phase gets underway. 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 three-year structural warranty cover?
The structural warranty is for a period of 3 years following completion, during which Build Team will guarantee the works against major structural defects.
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?
Ahead of signing a build contract with us our Build Director will review your Architect's drawings to make sure they are buildable. If there is something incorrect or missing from the drawing package — we will identify this to 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?
A Party Wall Notice will need to be served before you commence works if you are intending to excavate foundations within 3m of your neighbours' property.
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.