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Short answer: put every variation in writing before the work starts: describe the change, show how the price changes (not just a new total), state any delay, and get it signed or agreed in writing. NSW, Victoria and Queensland all require written variations on residential building contracts, and the QBCC lists variations that weren't recorded and approved before the work as a common cause of serious building disputes.

Facts checked against NSW, Victorian and Queensland Government sources on 21 October 2026. This is practical guidance, not legal advice; your contract's variation clause also applies.

At a glance

NSW

• Variations must be in writing, attached to the contract and signed by the homeowner and the builder (or the builder's nominated supervisor or agent).
• Show the cost implications. The document authorising a variation must explain the cost and its effect on the overall contract price, and the NSW Government says the calculation should be shown, not just a dollar figure.
• Urgent work: if there's likely danger to someone or damage to property, there may not be time to write it up first. The written variation can then be done after the work.
• Contracts are required for residential jobs over $5,000 (a small job contract up to $20,000, and a more detailed contract above that, including GST).

Victoria

• Agree in writing before work on the change starts, and record the new contract price and completion date in the contract. A variation notice is used to change the contract.
• The 2% exemption: no notice is needed if you reasonably believe the change won't require a permit change, won't cause delay and won't add more than 2% of the original contract price.
• Variations ordered by an authorised person (such as a registered building surveyor, inspector, engineer or architect): give the client a copy of the order and the variation notice. A client who disagrees must tell you in writing within five business days.
• Don't charge for what you should have foreseen. Consumer Affairs Victoria says clients shouldn't have to pay for variations needed to fix issues the builder should have identified before work started.
• Changing soon: the Domestic Building Contracts Amendment Act brings a single, simple process for variations on major domestic building contracts. The new laws take effect by 1 December 2026. Check Consumer Affairs Victoria before you rely on the current process.

Queensland

• A variation document must include a description of the variation, the date it was requested, whether it will delay the work, and any change to the contract price or the method for calculating it.
• Timing: give it to the owner in writing before the variation work starts, or within five business days of agreeing it, whichever comes first. The owner responds in writing.
• Urgent work (for example for safety) can go ahead first when it's not reasonably practicable to write it up beforehand.
• The QBCC's variation templates are usually Form 4 or Form 5, depending on your contract type.

How to price a variation

1. Describe the change against the original scope: what's added, what's removed and what's changed.
2. Price the added work: labour (hours × rate), materials, subcontractor quotes, and plant or equipment hire.
3. Credit the omitted work at the price in your original quote.
4. Add your margin (overhead and profit) on the added work, as your contract allows.
5. Add time-related costs if the job runs longer, such as extra supervision or equipment hire.
6. State the time impact and the new completion date.
7. Show the calculation line by line, then the new contract price.

Worked example

A kitchen renovation: the client adds two double power points and upgrades the benchtop, and drops the tiled splashback. Illustrative figures only.

Commercial fit-outs

Commercial jobs aren't covered by the residential rules above. They run under your head contract, often a standard form with its own variation clause, notice periods and deadlines for claiming. Follow that clause to the letter, and price the variation the same way: show the calculation, the time impact and a credit for anything omitted.

Your variation checklist

• Written down before the work starts (urgent work excepted)
• Clear description against the original scope
• Date the change was requested
• Price calculation shown line by line, including credits
• Time impact and new completion date
• Signed or agreed in writing by the client
• Filed with the job, with photos if the change is on site

Doing this in OpSpot

• Update the scope and generate a new quote version. Every version is kept: Q-001, Q-002 and so on.
• Compare two versions and download a variation PDF that shows what was added, removed and changed, zone by zone, as a dated record of the change (see Scope of works and quotes).
• Mark the signed quote as final and attach the signed document. You can still issue later variations against it.
• Use your contract's variation form or notice for the date requested, the time impact and signatures, and keep it with the job.

FAQ

Does a variation have to be in writing? On residential building contracts in NSW, Victoria and Queensland, yes, with limited exceptions for urgent work (and in Victoria, small changes under the 2% exemption). Even where it isn't required, writing it down is what gets you paid if there's a dispute.

Can I charge for a variation the client agreed to verbally? You risk not being paid. The written rules exist so both sides agree the change and its price before the work. Get it in writing first.

What's the difference between a variation and a provisional sum? A variation changes the work or the contract. A provisional sum is an allowance in the original contract for work that couldn't be priced yet; adjusting it to the actual cost isn't a variation to the scope (see the allowances section in our kitchen renovation scope of works template).

Should I add a margin to a variation? Usually yes, on the added work, if your contract allows it. Show it as its own line so the client can see how the price was built.

Sources

• NSW Government: Contracts for residential building work
• Consumer Affairs Victoria: Changing a domestic building contract price · New domestic building contract laws passed in Victoria
• QBCC: Contract variations