The owner may waive a provision of the contract providing for a certificate by the architect or engineer.1 Thus the conduct of the owner in inspecting and approving material about to be used by the contractor,2 or in taking charge of the building himself under a clause in the contract permitting him so to do,3 or in ignoring the clause providing for such certificate throughout the performance of the contract,4 or wrongfully breaking the contract and preventing performance,5 waives such provision. The fact that the owner has made one payment without requiring such certificate, does not waive the production of such certificate to obtain subsequent payment6 A certificate given by an architect for an installment which is to be paid when the building is completed, does not waive the production of his certificate for installments due by the terms of the contract thereafter.7