The inputs that matter most: per-flat build cost, per-flat post-conversion value or rental yield, fees and finance, planning context (probability and timeline of consent), and any structural complexity in the existing building.

If three of the five are clearly favourable and the other two are at least neutral, the project usually works. If two or more are marginal, the project usually doesn’t — at least not at the price the property is being marketed at.

A flat conversion feasibility appraisal pays for itself many times over.