The quality of an estimate is limited by the information behind it. You can price a project from very little, but the assumptions grow, and assumptions are where surprises live. Here is what actually makes the difference.
The essentials
- Floor plans — existing and proposed, with dimensions
- Elevations — so external finishes and openings can be measured
- Sections — the single most useful drawing for understanding build-up
- A written description of the works, even a short one
With those four things, most domestic projects can be priced to a genuinely useful level of accuracy.
Information that tightens the price considerably
Structural drawings and calculations
Steel sizes, foundation depths and slab construction move costs significantly. A steel beam assumed at 203 UB and delivered as a 305 UC with padstones is not a small difference, and neither is a 1.2m deep foundation where 900mm was allowed.
Specifications and schedules
Finishes are where budgets diverge fastest. £30/m² tiling and £120/m² tiling are the same drawing. If the client has chosen products, kitchens, sanitaryware or flooring, that information is worth more than another elevation.
Site photographs and existing conditions
For anything involving an existing building, photographs answer questions drawings never show: access for materials, where the scaffold goes, condition of what's being altered, whether a driveway can take a lorry.
Commercial information
- Tender documents and preliminaries where they exist
- The form of contract, if one is proposed
- Programme constraints or fixed completion dates
- Who is providing what — client-supplied items, free-issue materials, attendances
- Any planning or building control conditions with cost implications
What happens when it's missing
Nothing dramatic — this is normal. Missing information gets handled one of three ways: a stated assumption, a provisional sum, or a written exclusion. All three are honest. What is not acceptable is a number that quietly absorbs the risk without telling you.
Where something is both unknown and expensive, the right move is a conversation rather than a guess. That is why queries come back to you mid-estimate instead of appearing as a surprise at the end.
A simple rule
Send everything you have, even if it looks irrelevant or out of date. It is quicker to disregard a superseded drawing than to price around a gap. If you are unsure whether you have enough, ask — that review costs you nothing.