In design and construct contracts where an alternative tender is accepted, the expression identifying the contractor's alternative proposal may be given meaning by reference to extrinsic evidence of mutually known facts, including pre-contractual correspondence. A 'performance requirement' in a specification is a requirement expressed in terms of the outcome to be achieved, not a description of the means by which the outcome is to be achieved. When a court assesses an extension of time, it is not limited to a prospective analysis or to the material available to the superintendent; it may have regard to events as they actually unfolded. Time-related on-site overhead costs are recoverable as delay damages where the contractor proves the site was kept open for the period of the extension of time, without needing to show each cost item relates to work on the specific variation.
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