The contractor normally has no right to vary the works and the terms of the contract will specifically preclude this. But he can make suggestions as to how the work might be varied, for his own benefit or the benefit of the employer or both. He has no power to adopt his own suggestion; but if, say, he is unable to purchase an item required but finds an adequate substitute the engineer would no doubt agree. On occasion a good contractor will point out a change of design that has advantages, and the engineer should consider this because the knowledge of the contractor can assist in promoting a sound construction or reduced cost (see Section 17.1).
Situations can arise where the contractors work does not accord with the stated requirements. This may be by default when materials or equipment have been ordered and delivered only for it to be discovered that they are not in compliance with the specification. Or it may be that workmanship is found unsatisfactory only after some work has been built, such as concrete of too low a strength having been used in part of the structure. Under the contract the engineer has no option but to reject the work; but it may be to the advantage of progressing the works and preventing delay if the engineer discusses with the employer and contractor the possibility of accepting what has been provided, but at an adjusted price. Clearly this is not possible if the difference means the works will be unsafe or not usable for their intended purpose, but the employer may be able to accept a lower quality finish or the possibility of increased future maintenance if the cost of the works is reduced.
Any substitutions offered by the contractor should be referred by the resident engineer to the engineer, who will decide if the employers views should be sought. The employer is entitled to receive what was shown on the drawings and specified, and not something else. If any such change is to be accepted the full terms of agreement including price and time effects must be recorded in writing to avoid later arguments.