Lump sum vs. provisional sum, and why it matters

A lump sum item is priced and fixed — carpentry at a stated rate per metre run, for instance, won't change once the quotation is signed, regardless of minor site variations. A provisional sum is an allowance — electrical rewiring 'to be assessed on-site,' priced as a placeholder until the real scope is confirmed.

Both are legitimate. The problem is a quotation that uses provisional sums for items that should really be fixed, because the final number only gets locked in after work starts — by which point switching contractors is expensive and slow.

When you're comparing quotations, the number worth scrutinising isn't the total. It's how many line items are still provisional, and whether the reasons given for that are genuinely unknowable before site survey, or just deferred pricing.