Design and Build
Contractor in London

One firm for the drawing and the building

Design and build puts the design and the construction on a single contract. One organisation draws it, prices it and builds it, and therefore carries the risk of the gap between the drawing and the thing built from it. On a traditional appointment that gap belongs to you: when a detail proves undeliverable on site, the conversation about who pays for the redesign happens between your architect, your quantity surveyor and your contractor, with you in the middle of it and the programme stopped while it runs.

Crown Building has worked as a design and build contractor in London since 2013. Our largest commission to date is a £7m private residence on The Bishops Avenue in Hampstead, designed by Crown Building and constructed by Crown Building on one contract, from basement excavation and concrete frame through to panelled interiors and handover.

What design and build actually changes

The commercial argument is the one most contractors lead with: single point responsibility, no gap for a dispute to live in. The practical difference is faster and less visible. Decisions get resolved in days rather than in correspondence, and buildability is considered while the drawing is still on the screen rather than after the concrete has cured.

On the Bishops Avenue house that showed up in the details that are hardest to retrofit. The waterproofing fixing strategy was fixed at design stage, because every plug and service penetration through a tanked wall risks the system and the warranty behind it. The setting out for full height wall panelling was agreed before the frame was poured, so panel widths, door positions and light fittings resolved as one drawing rather than three. Neither of those is possible when the designer and the builder answer to different firms.

Design and build, or a contractor working to someone else's drawings

Neither route is automatically correct, and any building company that tells you otherwise is selling rather than advising. Traditional appointment gives you more direct control of the design and suits a client with a strong architect relationship worth protecting. Design and build gives you one accountable party and generally a firmer programme.

We work under both, under JCT, NEC and RIBA forms, and we will tell you honestly which we think fits your project when we have seen it. If you already have a scheme drawn and consented, contractor only is often the right answer and we will say so.

What a design and build contract costs

Cost per square foot is the only figure worth comparing between building companies, and it is the one least often published. We publish ours. Our contracts have run from £120,000 to £7m since 2013, with team capacity to £25m, but a range on its own tells you nothing. What moves the rate is access, constraint and specification, in that order.

Two completed contracts as real anchors. In Chelsea SW3, a complete interior transformation of a period property, 3,014 sq ft to ultra premium specification, at a contract sum of £1.1m, approximately £365 per sq ft. In Mayfair W1, the entire top floor of a landmark mansion block, 4,200 sq ft to the same standard, at £1.9m, approximately £452 per sq ft.

The same specification, a difference of £87 per sq ft, and almost all of that gap is logistics rather than finish: restricted delivery windows, a single goods lift shared with residents, protection regimes running the full programme, and freeholder consent before a fixing goes into a party structure. When you compare quotations from London building contractors, establish what each has assumed about access before you compare their rates. Both projects are documented in full on our Chelsea and Mayfair case studies.

The programme, and what actually moves it

A whole house refurbishment at this level generally runs nine to eighteen months on site; a new build eighteen months to three years. Those are honest ranges rather than optimistic ones, and the variation inside them is rarely caused by the construction.

Four things move a London programme and only one is on site: planning and listed building consent, which cannot be compressed by paying more; party wall awards, where one unresponsive neighbour holds a start date for months; long lead items, particularly stone, bespoke joinery and specialist glazing; and client decisions, which is the one nobody warns you about. A fortnight spent choosing a finish in month four becomes a fortnight added to the end. We programme all four explicitly at tender.

How the contract protects your money

You are handing a seven figure sum to a building company, and the sensible question is what happens if something goes wrong. We work under JCT, NEC and RIBA forms as standard, never on a letter of intent beyond the earliest enabling works. That gives you a fully itemised contract sum at tender rather than a lump figure, a defined variation procedure so changes are priced before they are built rather than argued after, retention held against defects, and liquidated damages if we overrun.

Ask any London building contractor you are considering for three things before appointing them: three years of filed accounts, insurance certificates with the limits visible, and the name of the person who will be on your site each week. Hesitation over any of the three tells you something. Ask us the same. Every enquiry here is handled by a director, and our free Project Assessor gives you a read on scope and complexity before you speak to anyone.

What we design and build

Ground up new build houses, whole house refurbishment, basement construction and excavation, listed and period property work, commercial fit out and bespoke joinery through Crown Bespoke. Published case studies across Mayfair, Chelsea, St John's Wood, Hampstead, Highgate, Mill Hill and Bushey Heath document the standard.

Areas we serve

All of London within the M25, Hertfordshire and selected Surrey addresses, from our Watford headquarters. Full coverage is on our areas we cover page.

Talk to a director

If you are planning a design and build project in London, call 020 3675 3999 or book a free consultation. Every enquiry is handled by a director.

Frequently asked questions

What is a design and build contractor?

A design and build contractor takes the design responsibility and the construction responsibility on a single contract. One firm draws the scheme, prices it and builds it, so a buildability problem is theirs to solve rather than yours to arbitrate between consultants. Crown Building works design and build or traditional contractor only, under JCT, NEC and RIBA forms.

Is design and build cheaper than a traditional contract?

Not automatically. It is usually firmer on programme and removes the cost of arbitrating between designer and builder when a detail does not work on site. Whether it is cheaper depends on the project. We will tell you which route we think fits yours.

What does a design and build project cost in London?

On completed contracts, approximately £365 per sq ft for a 3,014 sq ft period property in Chelsea and approximately £452 per sq ft for a 4,200 sq ft mansion block floor in Mayfair, both to ultra premium specification. The difference is access and constraint rather than finish. Our contracts have run from £120,000 to £7m since 2013, with team capacity to £25m.

What is the largest design and build project Crown Building has delivered?

A £7m private residence on The Bishops Avenue, Hampstead: five levels, three above ground and two below, designed and constructed by Crown Building on a single contract, from basement excavation and concrete frame through to panelled interiors.

How long does a design and build project take?

A whole house refurbishment generally runs nine to eighteen months on site and a new build eighteen months to three years. Planning and listed building consent, party wall awards, long lead items such as stone and bespoke joinery, and the speed of client decisions move the programme far more than the construction itself.

Which areas do you cover?

All of London within the M25, a 15-mile radius of our Watford headquarters, and the prime corridors of Surrey.