The interim valuation
The mechanism rests on a sequence of acts, each with its own time limits. Those limits are regulatory and overrunning them has effects.
The contractor periodically prepares an interim valuation listing the work executed, with corresponding quantities, accompanied by a statement of claim. That statement is the basis for the certificate that follows.
The client or their representative verifies, accepts or corrects, and draws up a certificate recording the works admitted to payment. That certificate fixes the quantities recognised at the date concerned.
The time limits framing these steps are regulated in public contracts, and exceeding them gives rise to interest. These are provisions from which derogation is regulated, as noted in the article on clarifications, additions and derogations.
Agreed measurement of quantities
This is the operation that gives the provisional quantity regime its meaning. It is the joint recording of the quantities actually executed.
Under that regime payment follows the quantities actually executed, not those entered in the bill. They must therefore be recorded, which presupposes observation on site, jointly, and a written trace.
Three principles apply.
Record at the right moment. Some quantities disappear beneath subsequent works. Earthworks, foundations or buried services cannot be measured after backfilling.
Record jointly. A quantity taken unilaterally is disputable, and it will be disputed.
Record in writing. A verbal agreement on a quantity does not survive a change of contact.
The practical rule that follows is simple: what is about to be covered is recorded before it is.
Variation or additional work
The distinction is fundamental and often blurred in everyday language. It separates a quantity adjustment from a variation of the contract.
| Variation | Additional work | |
|---|---|---|
| Origin | actual quantity differs from forecast | work absent from the contract |
| Item | exists in the bill | does not exist |
| Price | agreed rate | to be negotiated |
| Competition | played at award | absent |
A variation is the normal working of the contract. It requires neither prior agreement on price nor negotiation: the rate applies.
Additional work is a change to the contract. Its price is negotiated without competition, which is structurally unfavourable to the client, and that is precisely why a complete bill has value.
This distinction is developed in the article on who bears the risk of a quantity error. The three parties and their exposures are distinguished there.
The final account
At the end of the works, all recorded quantities are summarised and set against the original bill. The final account formalises that comparison.
That is when the gap between the contract sum and the sum actually due appears. Under the provisional quantity regime that gap is normal and expected. Calling it an overrun is a frequent error of analysis.
What deserves examination is not the existence of the gap but its nature: does it come from different actual quantities, from added work, or from items omitted at the outset. A quantity gap and a scope gap do not call for the same treatment.
Provisional acceptance triggers time limits
This is where the calendar overrides the merits, and it is regularly missed. The claim periods are short and run from notification.
Notification of the certificate of provisional acceptance starts a period after which certain claims are inadmissible. A contractor seeking a revision of the contract or damages must submit a quantified written justification at the latest ninety days from that notification.
Beyond that period the right is lost, however strong the case.
Other time limits and the regime of review clauses are covered in the article on provisional and lump-sum quantities. Their link with the final account is explained there.
What this means for a professional
Four rules.
Keep the bill current during construction, rather than reconstructing it at the end.
Record before covering, systematically, for any work due to disappear.
Distinguish variations from additional work explicitly in documents, since they do not follow the same pricing regime.
Note the date of provisional acceptance and the time limits it triggers, from notification.
This article reflects the position of the rules at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.