Construction Glossary
Provisional Sum
Definition
A provisional sum is a figure included in a price for work that cannot be fully measured or designed yet. It is an allowance, not a fixed price, set aside so the budget reflects work that is still uncertain. When the detail is known the actual cost replaces the allowance and the contract value is adjusted. RICS NRM splits these into defined and undefined provisional sums.
Provisional sums cover work that is known to be needed but not yet fully designed, such as unforeseen groundworks or a specialist installation still being specified. They keep the budget honest by reserving money for it without pretending it is fixed.
Under RICS NRM a defined provisional sum comes with enough information for the contractor to allow for programme and prelims, while an undefined one does not, which affects later claims for time and cost.
Why it matters
Used well, provisional sums stop you from either guessing at an unknown or leaving it out entirely. Used badly they hide the true cost of a job. Knowing the difference between defined and undefined sums protects you from disputes over extra time and money when the real figure lands.
We identify and clearly label provisional sums in your estimate so uncertain work is allowed for properly and adjusted fairly later.
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