An extension of time is a notice, then a proof

An extension of time adjusts the date for completion when something outside the contractor control delays the works. It is not extra money on its own, it is protection. Without it the original date stands, and liquidated damages start running against a contractor who was delayed by something that was not its fault.

Notice comes first

Under NZS 3910:2023 the extension mechanism runs through the Engineer to the Contract, and it starts with notice. The contractor has to notify the delay event and its likely effect on the programme within the contractual timeframe. A late notice weakens the claim, and a claim that only surfaces at the final account rarely survives.

• The event. What happened, when, and why it falls under the contract as grounds for an extension.
• The effect. How the event delayed completion, shown against the accepted programme.
• The records. Site diaries, correspondence and progress data that fix the event in time.

Cause tied to effect

The Engineer assesses the extension by looking at whether the event actually delayed completion, not just whether it happened. That means the claim has to link the event to the critical path. A delay to work that had float behind it may not move the completion date at all. The programme is where that argument is won or lost.

Time and money are separate

An extension of time protects the programme. It does not automatically bring cost with it. Where the delay also caused the contractor to incur additional cost, that is a separate claim on its own grounds, valued and, where it belongs on the works, carried into a payment claim. Keeping the two questions apart keeps both cleaner.

Why it matters for the account

The extension sets the completion date, and the completion date drives practical completion, the start of the defects period and the release of retention. Get the extension wrong and every downstream date drifts with it. Where the Engineer assessment is disputed, adjudication under the Construction Contracts Act 2002 is open to the contractor.

The discipline

Notify early, keep the programme current, and build the cause and effect while the event is fresh. The extension you can prove is the extension that holds, and the damages you avoid are worth more than the notice ever cost to write.