What is an open-book estimate?

An open-book estimate breaks a renovation into its real elements with a figure and its basis against each, stating what is measured, what is a provisional allowance and what is excluded — so the client can interrogate the price rather than take a single number on trust.

What should I check first in a renovation quote?

The exclusions. Every figure should state its basis and specification, but the items excluded outright are where most disputes begin — and a quote that does not list its exclusions is not complete enough to compare against another.

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What an Open-Book Estimate Actually Shows You

5 hours ago
3 min read

A single-figure quote asks you to make the largest purchase of your life on trust. You cannot see what is in it, what is missing from it, or where it will bend when the project meets reality. An open-book estimate is the opposite discipline: the builder shows the working — what each element costs, what assumptions sit underneath, and where the genuine uncertainties are. Once you have seen one, a one-line quote starts to look like what it usually is: a number chosen to win the job, with the truth deferred to the variations.

What the open book contains

A proper open-book estimate breaks the project into its real elements — demolition, structure, external envelope, services, internal finishes, joinery, external works — with a figure and its basis against each. It states what is measured, what is allowed as a provisional sum, and what is excluded outright. The exclusions are the most valuable page: every renovation dispute we have ever been asked to untangle began life as an exclusion nobody read.

It also shows where the risk lives. Ground conditions, hidden services, the condition of what the strip-out reveals — an honest estimate names these instead of pretending they do not exist, so the contingency is a decision you make rather than a surprise you absorb.

Bespoke dressing room in champagne-oak illuminated joinery with a central island and mirrored drawers, Knightsbridge SW1

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 — and 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 — like our guides to rear extension and loft costs — give you an external yardstick to hold any line item against. A figure far outside the band, in either direction, deserves a very good explanation. If you would like a second pair of eyes on an estimate you already hold, we will read it with you: nuprojects.co.uk.

Living room with a restored period fireplace, drum chandelier and sash windows in a Knightsbridge SW1 apartment

Why the contract shape matters as much as the estimate

Transparency at estimate stage only survives if the delivery model protects it. Where design and construction sit with separate firms, 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 is the team that has to build it, which 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, with over 100 prime central London projects delivered under one contract — architecture, interior design, project management and construction in one accountable team. If you are comparing quotes for a London renovation and one of them is a single number on a single page, bring it to us and we will show you what the open version of it looks like: nuprojects.co.uk · 020 7731 6841.

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