Open-book estimate for a London renovation

A single-figure quote asks you to buy on trust. It may be the largest purchase of your life. You cannot see what is in it. You cannot see what is missing from it. Nor can you see where it will bend when the project meets reality. An open-book estimate is the opposite discipline. The builder shows the working. It shows what each element costs and what assumptions sit underneath. It also shows where the genuine uncertainties are. Once you have seen one, a one-line quote looks like what it usually is. It is a number chosen to win the job. The truth is deferred to the variations.

What the open book contains

A proper open-book estimate breaks the project into its real elements. These are demolition, structure, external envelope, services, internal finishes, joinery and external works. Each has a figure and its basis against it. It states what is measured. It states what is allowed as a provisional sum. It also states what is excluded outright. The exclusions are the most valuable page. Every renovation dispute we have untangled began life as an exclusion nobody read.

It also shows where the risk lives. An honest estimate names ground conditions and hidden services. It also names the condition of what the strip-out reveals. It does not pretend they do not exist. So the contingency is a decision you make rather than a surprise you absorb.

The questions the format lets you ask

With the working visible, you can finally interrogate a price like a professional would. Which figures are measured and which are allowances? What specification is each figure based on? Is that the specification you actually want? What happens to the number if the dig finds soft ground? Which items are excluded, and who is expected to carry them?

Benchmarks make those questions sharper. Published per-square-foot bands give you an external yardstick to hold any line item against. Our own rates by work type are in the NU Build Cost Calculator. The detail behind two is in rear extension cost and loft conversion cost. A figure far outside the band, in either direction, deserves a very good explanation. You may like a second pair of eyes on an estimate you already hold. If so, send it to us and we will read it with you.

Why the contract shape matters as much as the estimate

Transparency at estimate stage only survives if the delivery model protects it. Design and construction may sit with separate firms. Then a gap between the drawings and the price is always someone else’s fault. The architect-led and design and build routes split that risk very differently. Under one contract, the team that priced the job must build it. That is the strongest incentive for the estimate to be right the first time.

See the working before you sign

NU Projects is a design and build practice established in 2010. Architecture, interior design, project management and construction sit in one accountable team. They work under one contract. You may be comparing quotes for a London renovation. One of them may be a single number on a single page. If so, bring it to us. We will show you what the open version of it looks like. Call 020 7731 6841.

Holding a quote you cannot interrogate? Book a consultation or call 020 7731 6841. Bring us the estimate you already have. We will show you what the open version looks like, line by line.