These usually have a requirement to give notice of the claim within a certain period of time and are often a trigger for a claim for delay costs. Most contracts also include a clause allowing the owner’s representative or an independent certifier to extend time for completion unilaterally at their discretion. The latter clause is not there as some sort of codified waiver. It exists to account for the prevention principle. The prevention principle says that a party cannot rely on a breach of contract where its own actions have caused the breach. Therefore if the reason, or one of the reasons, a contractor has failed to reach completion by the date specified is it was prevented from doing so by the owner, the owner cannot levy liquidated damages from that date. The prevention principle has been recorded in the common law for centuries, in both a construction context and more generally in all commercial contracts. One of the functions of extension of time clauses is to provide a contractual mechanism to avoid the operation of the prevention principle and so preserve the owner’s right to liquidated damages. That is, if the delay caused by the owner can be separated out from the overall delay which has occurred, the owner can still hold the contractor responsible for the remaining delay, without offending the prevention principle. So, in the typical contract being considered, if prevention occurs, a contractor may claim an extension of time. That may also give the contractor a right to claim delay costs. But if the contractor does not validly claim an extension of time, the unilateral extension of time power nevertheless allows the owner to grant an extension of time for delay caused by prevention, in order to separate out that delay. The owner can then insist upon completion by the new, extended date. If the contractor fails to complete by the extended date for completion, that is no fault of the owner. The owner can levy liquidated damages without offending the prevention principle. In Peninsula Balmain,[1] followed by 620 Collins Street,[2] the courts held that, where the contractor failed to make a valid claim for an extension of time, the independent certifier (in those cases, the superintendent) was obliged to exercise the unilateral extension of time power[3] for the period of delay caused by the owner. This was because of an express contractual obligation for the independent certifier to act honestly and fairly in the administration of the contract. The decision in Probuild v DDI The matter before the court DDI was a plasterboard subcontractor on a hotel redevelopment for which Probuild was head contractor. DDI completed 144 days after the date for completion. It made a significant Security of Payment claim for costs on account of variations (around $2.2 million on an original contract value of around $3.4 million). DDI had not made claims for extensions of time, nor complied with strict notification procedures for variations. Probuild responded to the claim by setting off liquidated damages. DDI argued the contractual mechanisms had been abandoned. The parties’ submissions pointed to a range of potential causes of delay. The adjudicator decided that in circumstances where variations had been directed after the date for completion had passed, it was ‘unreasonable’ for Probuild to not have granted an extension of time. Even if some delays had been caused by DDI, this meant Probuild had not established its claim for liquidated damages. The adjudicator decided Probuild was liable for around $0.5 million.