Acceptance window (variations)
An acceptance window is the period (typically 5 working days under HIA/MBA) for an owner to sign and return a variation offer. Don't start work until it's signed back.
Ask Chalkline about this →An acceptance window is the period in which the owner must sign and return a written variation offer for it to take effect. It is a defined step in the contract’s variation procedure: the builder serves the written variation offer, and the owner has a set number of working days to accept it. Once the window closes without a signed acceptance, the offer lapses.
Under HIA contracts (clause 18 in NSW) and MBA contracts (BC4 clause 14), the owner has five working days to sign and return the builder’s variation offer. The practical rule that goes with it: do not start the varied work until the signed document is back. An unsigned variation gives the owner a basis to refuse payment for the extra work (under the Home Building Act 1989 (NSW) Schedule 2 and equivalent state rules), and chasing payment then becomes a quantum meruit fight, which is harder and more expensive than a properly signed variation.
There is one narrow exception: urgent work needed to prevent injury, property damage, or legal non-compliance, where it is not reasonably practicable to get prior written agreement. Even then, you produce and serve the written variation as soon as practicable afterwards. For everything else, serve the offer, track the acceptance window, and hold off on the work until the owner has signed and returned it. See variations process.
Also known as: Variation acceptance window, sign-back window.
Category: Contracts / Variations.
Related
See also
References
- Home Building Act 1989 (NSW), Schedule 2 (verified 2026-05-09)
- HIA: Contracts Online (variation provisions) (verified 2026-05-09)
Last updated: 2026-05-30. Verified: 2026-05-09. Quarterly review for currency.