Provisional sums

The following Construction practice note provides comprehensive and up to date legal information covering:

  • Provisional sums
  • What are provisional sums?
  • Why are provisional sums used?
  • Concerns with using provisional sums
  • How is provisional sum work valued?
  • What happens if a provisional sum is not instructed?
  • Provisional sums in the standard forms
  • JCT
  • NEC3/NEC4
  • More...

Provisional sums

What are provisional sums?

There is no precise standard definition of provisional sum but it is generally understood to refer to an amount inserted in a bill of quantities, or contract sum analysis, to cover certain items of work that cannot be accurately defined, detailed or valued at the time that the tendering documents are issued by the employer. This could be because the item of work may not be required or the extent/scope of it is undefined—for example, if the contract works include excavation or underground work that cannot be properly investigated until the project has commenced. It is called a ‘provisional’ sum because neither party is held to the figure—the actual figure may be higher or lower than the provisional sum stated.

In Midland Expressway v Carillion Construction, the Court of Appeal described a provisional sum as being:

'used in pricing construction contracts to refer either to work which is truly provisional, in the sense that it may or may not be carried out at all, or to work whose content is undefined, so that the parties decide not to try to price it accurately when they enter into their contract’

Some contracts distinguish between ‘defined’ and ‘undefined’ provisional sums, for example, the JCT Standard Building Contract with Quantities 2016 (SBC/Q) adopts the definitions from paragraph 2.9.1 of the New Rules of Measurement—Detailed Measurement for

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