How to Choose a Design and Build Company
Six questions that separate a design and build company from a company that subcontracts both halves and hopes. What to ask, and what a straight answer sounds like.
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From our Amott Road project — Peckham, SE15
There is 1 question that separates a design and build company from a company that subcontracts both halves and hopes: who employs the designer, and who carries the design risk. Everything else on the comparison spreadsheet is downstream of that answer.
Most advice on choosing a builder is a list of things everybody already knows — get three quotes, check insurance, see previous work. None of it is wrong. None of it distinguishes between two companies that both have a website, both have photographs, and both seem pleasant on the phone.
What follows is the shorter list that actually sorts them.
The question, and what a straight answer sounds like
Ask: who does the design, and who is responsible if the design turns out not to work?
The distinction matters most on the day it is inconvenient. Everybody is aligned in week one. The test is week nine, when a steel is deeper than the drawing assumed and the ceiling height in the room you cared about is now lower than you were shown. Under one structure that is a conversation. Under another it is two companies explaining why it is the other one's fault, with you in the middle adjudicating a technical argument you are not equipped to judge.
That is the whole substance of the choice, and it is covered at length in who carries the gap between the drawings and the building.
Six checks, in the order worth doing them
- 01Who employs the designer?. Asked above, and it is first because the other five only matter once you know the answer.
- 02Which contract form, and what edition?. Not 'a JCT contract'. The name and the year. For most London extensions the honest answer is Minor Works — what that means is set out in our piece on JCT design and build.
- 03Professional indemnity certificate, not a statement.. The only policy that responds to a design error. Ask to see it, and check design is inside the scope rather than assuming it.
- 04How are variations priced, and when?. The answer you want is that nothing is charged without your written approval, with the price agreed before the work happens rather than valued afterwards.
- 05What are the exclusions in this quote?. A quote that names its exclusions is usually closer to the final figure than one that reads as all-inclusive. Provisional sums are decisions nobody has made yet, not prices.
- 06What went wrong on your last job?. Ask the company, then ask their references the same question. The answers should roughly match. A company that has never had anything go wrong has not done many projects, or is not telling you about them.
Key takeawayDo not ask a reference whether they were happy. Ask what went wrong, how long it took to fix, and who paid. Every real project has that moment, and how it was handled is the only part of a reference worth having.
Where the money question actually belongs
Comparing totals across quotes is the least useful thing you can do with them, because a total is a function of scope and nobody's scope is identical.
Compare, in this order: what is included, what is explicitly excluded, how many provisional sums are standing in for unmade decisions, and what the programme assumes about what will be found behind the plaster. Then compare the numbers.
Most of the difference between two quotes for the same house is not margin. It is a different set of assumptions about the same building, and the cheaper one is frequently the one that has assumed more.
- Stage 1: Choose the procurement route before you develop the design. Deciding this late throws away most of the benefit of whichever route you pick.
- Stage 2–3: Shortlist. This is the stage for the six questions above, while you still have leverage and before anyone has drawn anything expensive.
- Stage 4: Contract particulars — dates, retention, defects period, how variations are valued. The paperwork people skim and then argue about.
- Stage 6–7: Handover and the defects period. This is when you find out whether 'local enough to come back' was a real answer.
What we would say about ourselves, and the caveat
We are the builder and the design sits with our design and build service rather than with a firm we introduce you to, so there is one contract and one company answerable for both halves. Variations are priced and signed before the work happens, never charged without your written approval. How we run a project is written down so you can check it against what actually happens rather than take it on trust.
The caveat is the same one we would apply to any company answering these questions well: our designer is on our side of the table. If the architecture is the entire reason for your project, appoint somebody independent to hold us to the drawings. That costs you a fee and it buys you a second opinion from someone with no stake in the build programme. It is often worth it, and a contractor who resists it is telling you something.
If you want a range before any of this, the estimator prices off the same rate card we contract from — wide at first, narrower as you answer more.
Straight answers
The home you actually want, finished on the date in the contract — and you watch every day of it happen from your phone.
You answer 3 questions. We do the drawings, planning, party wall, trades and snagging.
- 10% to mobilise, then weekly against work already done — with 5% held past handover: 2.5% released at practical completion and 2.5% at the end of the 12-month defects period
- £550 survey fee credited in full against your contract
- Every variation priced and signed before a penny is spent
No email needed to see your range. Quotes hold for 21 days, then materials re-price.
We are not the cheapest. If price is the only factor, we may not be the right fit — and that is fine.
Keep reading
- Design and Build London: Stage by StageWhat happens on a design and build project in London, from the first call to the end of the defects period — and which decisions cost money if they slip a stage.
- JCT Design and Build: What You Will SignJCT Design and Build is a real contract with a real design-liability clause — and almost certainly not the one your London extension will be built under.
- Commercial Design and Build Companies, LondonWhat commercial design and build actually buys you on a London workplace project, what it does not, and the questions that separate a contractor from an introducer.
- What the Skip Costs: Strip-Out, Landfill Tax and the Waste You Design InLandfill tax is £130.75 a tonne from April 2026. A fit-out that sheds 3.5 tonnes pays £463 in tax alone before the skip, the lorry or the labour.