Most London residential renovation and extension projects are delivered through one of two broad procurement routes: traditional procurement, where the client appoints an architect separately from a contractor; or design and build, where a single organisation is responsible for both design and construction under one contract.
Under traditional procurement, the architect produces a design that the client approves at each stage. Once the design is sufficiently developed, the contractor is appointed through a tender process or negotiated agreement. The architect typically acts as the contract administrator during construction, reviewing work quality, certifying payments, and issuing instructions for variations on the client's behalf. The design liability rests with the architect; the construction liability rests with the contractor. The client has separate professional relationships with each.
Under design and build, the client appoints a single contractor who takes responsibility for producing or coordinating the design and delivering the construction. The design team — architects, structural engineers, and specialists — work for the contractor rather than the client. The single point of contact simplifies the client relationship and can reduce coordination gaps between design and construction. But it also means the client has less independent professional oversight during construction, and design changes late in the process are typically more difficult to implement.
For smaller residential projects — extensions, loft conversions, refurbishments under roughly five hundred thousand pounds — the distinction in practice is less stark than in theory. Most clients in this market appoint their own architect to produce planning and building regulations drawings, and then appoint a principal contractor to build. The contractor coordinates with the architect and structural engineer but does not design from scratch. This is sometimes called a traditional route but with a design-aware contractor — which is the most common form of residential project delivery in London.
The benefit a design-aware principal contractor adds over a basic building-only contractor is significant: knowledge of what the design means in construction terms, early identification of buildability issues or coordination problems between the architect and structural engineer, and an understanding of how design decisions affect both cost and programme. This is what RCB provides — not a purely separate architectural service, but integrated design-construction thinking that reduces surprises on site.
For homeowners choosing between routes, the key questions are: how much design control do you want to retain, and how much independent professional oversight do you want during construction? If both are high priorities, traditional procurement with an independent architect and a separate contractor works well. If you want a simpler single point of accountability and a contractor who can guide design decisions from a construction perspective, a design-aware principal contractor in a collaborative role is often a better experience.
RCB works collaboratively with clients and their architects throughout the design process and takes principal contractor accountability for delivery. 07359 872594 | contact@rcbgroup.co.uk | www.rcbgroup.co.uk