How to price a rebuild you have never priced

The two figures are unrelated and they move in opposite directions more often than people expect. A building in a weak location can be worth less than it costs to rebuild; a building on expensive land can be worth far more. Insurance pays to reinstate, so market value is the wrong number to start from.

What the figure has to include

Demolition and site clearance. Professional fees for architects, surveyors and building control. The cost of complying with current building regulations, which are almost always stricter than they were when the building went up. Inflation across the rebuild period, because a large reinstatement takes eighteen months and prices move while it happens.

Leave any of those out and the figure is light by a predictable amount. Professional fees alone typically add 10 to 15%.

When an estimate is enough

For a small, modern, standard-construction unit, a per-square-metre estimate from a current cost guide is defensible. For anything listed, unusual, or over about a million pounds, get an assessment. The rule of thumb is that the more interesting the building is, the worse an estimate performs.