Variations to NSW residential building contracts: written and signed under the Home Building Act 1989

What a variation is

A variation is any agreement between a builder and homeowner to change the scope, materials, finishes or price of work that was set out in the original residential building contract. Variations come up on almost every job. Homeowners change their mind about a tile, the builder discovers an unforeseen site condition, a council condition requires an adjustment, the homeowner asks to add a feature. The legal question is not whether variations happen but how they are recorded.

The Home Building Act 1989 (NSW) takes a strict line. Variations must be in writing and signed by or on behalf of each party before the work is done. A handshake or a verbal agreement in the kitchen is not enough.

The legal rule

Section 7E of the Home Building Act requires every residential building contract to include the mandatory terms set out in Schedule 2 Part 1 of the Act. One of those mandatory terms is that any agreement to vary the contract, or to vary the plans and specifications for the work, must be in writing signed by or on behalf of each party.

This rule does two things. It overrides any contract clause that purports to allow oral variations. It also makes the written-and-signed test the legal gate for whether a variation is part of the contract at all.

What a compliant variation looks like

A compliant variation document identifies the work being added, removed or changed in enough detail that a reasonable third party reading later can identify what was agreed. "Upgrade tile to porcelain in main bathroom" works. "Extra tile work" usually does not.

It states the price impact. A specific dollar amount inclusive of GST, or a clearly stated rate where the work is paid hourly or per unit.

It states the time impact if any. Variations that affect the program need to extend the contract completion date in writing.

It carries the date and signatures of both parties or their authorised representatives. Email exchanges that exchange the variation in writing and are countersigned by reply or attached PDF can satisfy the written-and-signed test. A single email saying "go ahead" without a counter-signature is risky.

Consequences of unsigned variations

If a variation is not in writing and signed before the work is performed, the builder cannot rely on it as part of the contract to recover payment. Courts have repeatedly held that the Home Building Act mandatory written-and-signed term operates to deny the builder the contractual remedy.

There are limited equitable remedies available outside the contract. A quantum meruit claim for the value of the work done is the usual fallback. But equitable remedies are harder to win, take longer to resolve and produce uncertain results. Some courts in NSW have allowed quantum meruit recovery where the builder can prove the homeowner clearly agreed to the work and benefited from it. Recent appellate decisions have narrowed that path. The safest assumption for a residential builder is that if it is not in writing and signed, it is not getting paid as a variation.

Variations to plans and specifications

The mandatory written-and-signed rule applies to changes to the plans and specifications, not just changes to the scope or price. A homeowner who asks for a different window manufacturer mid-build is varying the specification. The variation needs to be recorded the same way as a scope change.

This catches builders out where the change is small and seems administrative. A different brand of tap, an upgraded light fitting, a substituted timber species: each is a specification variation and each needs the signed document trail to be enforceable as part of the contract.

Price-variation clauses

Cost-plus contracts, contracts with provisional sums and contracts with prime cost items all involve a price that is not fixed at signing. Section 7E requires the contract to include a warning that the price may be varied and an explanation of how the variation works. The warning must be placed next to the price if a price is shown and must use the prescribed language.

For prime cost items, the contract typically lists an estimated allowance. Variations against the estimated allowance, once the actual item cost becomes known, are documented in writing and signed by both parties so that the actual cost flows into the final contract price cleanly. The same approach applies to provisional sums and to provisional cost allowances.

Practical advice for builders

Three habits make variation administration painless.

Use a numbered variation form. Both HIA and Master Builders standard contracts include or accompany variation forms with the right structure. Number them so the contract administration trail is clean and so progress claims can reference specific variation numbers rather than vague descriptions.

Document and sign the variation before performing the work. Once the bathroom is tiled it is too late to argue about whether the upgrade was agreed. The legal protection for the builder lies in the prior signature, not in the finished workmanship.

Keep variations short and itemised. A single variation that bundles five unrelated changes makes it harder to dispute one without questioning all five. Five separate variation documents, each signed, is the cleaner audit trail when a dispute arises.

Related entries

The choosing-residential-building-contract entry covers contract selection including which standard forms handle variations well. The cooling-off entry covers a separate consumer-protection mechanism that applies at contract signing. The progress-payment-rules entry covers how variations interact with the staged payment regime under section 8A of the Act.