The contractors monthly application for interim payment is usually set out as shown in Fig. 13.4. Initially only the items under which work has been measured need be listed, divided into bills. Later, when all the work listed on a page of the bill of quantities has been completed, the page total only need be quoted in the bill summary. Where work is incomplete and only an estimate can be made of the work done, the RE may accept the contractors figures if they are reasonable. But where work is completed, the contractors final measurement of a quantity should check reasonably with the REs estimate. In such matters as excavation the RE should not require an unreasonable degree of accuracy, measurement to the nearest 1m3 is adequate. For minor differences between the contractors figures and the REs, a compromise figure may be agreed. Major differences should be looked into.
To aid estimating the probable final cost of the works (see Section 14.9) it is best if extra items are put on a separate sheet or sheets, grouped for each separate bill of quantities, where possible. Extra items not authorized by a previously issued variation order (VO) must be checked by the RE. If he agrees them he must send a draft VO to the engineer to cover them.
If he thinks an extra is invalid, or the rate or quantity is wrong, he should discuss this with the contractor, and may decide to delete the item, accept it, or substitute a rate or quantity he considers fair. He draws the engineers attention to his decision when forwarding the contractors payment application to him. If the contractor continues to dispute the item after the engineers decision on it, the matter becomes a claim, is given a number and put on the Claims Pending file for further consideration.
It is preferable for each VO to cover one instruction only. However, one VO can be made to cover a series of related instructions, provided the instructions covered are itemized. A typical style of VO is shown in Fig. 13.5.
