Re-measurement types of contract, such as those covered by the ICE 7th edition (Measurement Version), are let on the basis that the actual amount of work done is not expected to be exactly the same as that estimated from the contract drawings.
The intention of the contract is that where a change of quantity requires no different method of working by the contractor and does not delay or disrupt his work then the billed rates still apply. However, Clause 56(2) of the ICE conditions recognizes that, if there is a considerable difference between the measured and billed quantity, the contract allows a review of the rate to ensure that a proper price is paid. If the engineer is of the opinion that a quantity has changed so much that ‘any rates or prices (are) rendered unreasonable or inapplicable in consequence’, then the engineer, after consultation with the contractor, can increase or decrease such rates or prices. The change in quantity has to be significant to justify an altered rate.
In some international contracts, any review of rates or prices is restricted to changes in individual quantities exceeding a given percentage. If it were intended that all changes in quantity justified a different rate, then the rates would largely become irrelevant. In practice therefore rates are seldom altered for what might be termed ‘natural’ variation of quantities. Most variations that are large enough to require re-consideration of rates stem from an instruction issued by the engineer or resident engineer and this is a different matter dealt with in Section 17.4. Occasionally an item gets missed from a bill, which the contract or method of measurement provides should have been measured.
Rates for these must also be set by the engineer in the same manner, but without there being any instructed change.