25 Before dealing with the grounds of appeal, I propose to address a submission put by the respondent for the first time on appeal. As I understand it, the submission is to the effect that, on a proper construction of the building contract, the respondent's obligation was to construct the house on site works provided to it by the appellant without regard to whether the sand pad level complied with the contract plans. I do not accept that submission. It is the case, as the Commissioner found, that the appellant was contractually obliged to do the site works. Additionally, the appellant's contractual obligation was to do the site works in accordance with the contract plans. That must be the case having regard to the respondent's express obligation to construct the house in accordance with, inter alia, the contract plans. It follows that the appellant's obligation to provide the respondent with a sand pad at 14.5 m was not a condition exclusively or even primarily for the appellant's benefit which it was entitled to unilaterally waive (see Greig and Davies, The Law of Contract at 375; Chitty on Contracts: General Principles Vol 1, 29th ed at [22-045]). For a helpful discussion of the relationship between waiver, variation, election and estoppel, see Greig and Davies at 120 - 124. Further, this is not a straightforward case of the respondent "waiving" the appellant's breach in failing to provide site works at the agreed level because the respondent proceeded to construct the house at the reduced level notwithstanding its inconsistent contractual obligation under the building contract.