What is a variation in a building contract?
A change to the work after the contract is signed, and what each state's law asks before it goes ahead.
A variation is a change to the work in a signed building contract — work added, taken out or done differently — together with what it does to the price and the finish date. Most states' building Acts require it in writing and signed: in New South Wales by or on behalf of each party (Schedule 2, Part 1, clause 1(2)); in Victoria by the owner's signed consent or signed request before the builder gives effect to it (sections 37(2) and 38(5)); in Queensland by the owner's written agreement before the varied work starts (Schedule 1B, section 40(5)). In the ACT and the Northern Territory no statute sets rules for variations, and the contract's variation clause governs.
Not legal advice — your contract's own variation clause matters too.
The law in each state
The Act each state's variation rules sit in, the contracts they apply to, and what they ask for: the agreement in writing, what has to happen before the varied work, and the owner's copy.
| State | Act | Applies to | Agreed in writing | Before the varied work | The owner's copy |
|---|---|---|---|---|---|
| New South Wales | Home Building Act 1989 (NSW) | Any job over $5,000 including GST; the full written-contract rules over $20,000 (sections 7 and 7AAA; Home Building Regulation 2014, clause 5) | In writing, signed by or on behalf of each party (Schedule 2, Part 1, clause 1(2)) | Not required by the Act | Not stated for variations |
| Victoria | Domestic Building Contracts Act 1995 (Vic) | Major domestic building contracts, over $10,000 (Domestic Building Contracts Regulations 2017, regulation 6) | The builder's notice and the owner's signed consent attached to a copy of it; for a variation the owner asks for, the owner's signed request (sections 37(2) and 38(5)) | The builder must not give effect to it until the owner's signed consent or request (sections 37(2) and 38(5)) | Not specified |
| Queensland | Queensland Building and Construction Commission Act 1991 (Qld) | Regulated contracts over $3,300: level 1 under $20,000, level 2 at $20,000 or more (Schedule 1B, sections 6 and 7; QBCC Regulation 2018, section 45) | The owner agrees to it in writing (Schedule 1B, section 40(5)) | The builder must not start the varied work before the owner agrees in writing; 20 penalty units (Schedule 1B, section 40(5)) | Before the earlier of 5 business days after the agreement and the start of the varied work; email is allowed (Schedule 1B, sections 40(2) and 40(3)) |
| Western Australia | Home Building Contracts Act 1991 (WA) | Home building contracts between $7,500 and $500,000 | In writing, dated and signed by the builder and the owner (section 7(1)) | The owner's copy before the varied work starts (section 7(2)) | Before the varied work starts (section 7(2)) |
| South Australia | Building Work Contractors Act 1995 (SA) | Contracts over $20,000 (contracts from 10/11/2025) | In writing and signed by both parties: a variation is a contract of its own (sections 3 and 28) | Not required by the Act | As soon as practicable after both parties sign (section 28) |
| Tasmania | Residential Building Work Contracts and Dispute Resolution Act 2016 (Tas) | Contracts over $20,000 | A written variation document signed by both parties (section 19) | Where it adds work, in place before that work begins (sections 17 to 21) | Within 5 business days (section 20) |
| Australian Capital Territory | Building Act 2004 (ACT): no variation rule | Residential building contract requirements from $12,000 (regulation 37) | The contract's clause governs | The contract's clause governs | The contract's clause governs |
| Northern Territory | Building Act 1993 (NT): no variation rule | Residential building contract provisions: a $25,000 threshold (section 48B; regulations 41H and 41J) | The contract's clause governs | The contract's clause governs | The contract's clause governs |
Who asks for a variation
Either party can ask for one, and a law or an authority can require one. Victoria sets different steps for each. A variation the builder wants needs a notice and the owner's signed consent (section 37). One the owner wants needs the builder's notice of its effect, any delay and its cost, and the owner's signed request (section 38) — unless the builder reasonably believes it won't need a permit change, won't cause any delay and won't add more than 2% to the original contract price, when the builder may carry it out (section 38(2)). A variation a building surveyor requires in a building notice or order has its own route (section 37(2)).
A variation or an allowance
A prime cost item is an allowance in the contract for something not yet selected, or whose price isn't known, such as a fixture or fitting; a provisional sum is an estimate of the cost of work the builder can't give a definite amount for when the contract is signed. Victoria (section 3) and Queensland (Schedule 1B, sections 1 and 10) define both in close to the same words.
When the actual cost comes in, the contract's own clause on allowances sets how the price moves. In Victoria, sections 37 and 38 don't apply to contractual terms dealing with prime cost items or provisional sums (sections 37(5) and 38(8)), so an adjustment there isn't a variation under those sections.
Does a variation have to be in writing?
New South Wales
Yes, on any job over $5,000. The Act puts a term into every home building contract it covers (Schedule 2, Part 1, clause 1(2)): any agreement to vary the contract must be in writing, signed by or on behalf of each party. The term reaches small jobs over $5,000 as well as contracts over $20,000 (clause 1(3), through section 7AA). If it's only been agreed on site, ask for it in writing, priced, and sign it before the work goes ahead.
Victoria
Yes. A builder who wants a variation must give you a written notice (section 37(1)) and must not go ahead with it unless you give a signed consent attached to a copy of it (section 37(2)). For a variation you ask for, the builder may go ahead without a notice only if they reasonably believe it won't need a permit change, won't cause any delay and won't add more than 2% to the original contract price (section 38(2)); otherwise they must give you a notice of its effect, any delay and its cost, and wait for your signed request (sections 38(3) and 38(5)). These rules apply to major domestic building contracts, over $10,000.
Queensland
Yes, on a regulated contract over $3,300 — level 1 or level 2. The builder must not start the varied work before you agree to it in writing (section 40(5)), and must give you a copy in writing before the earlier of 5 business days after you agree and the start of the varied work (section 40(2)). It can be given by email (section 40(3)).
Western Australia
Yes. Section 7(1): a variation must be in writing, set out all of its terms and its cost, show its date, and be signed by the builder and the owner. You get a copy before the varied work starts (section 7(2)). The Act covers home building contracts between $7,500 and $500,000.
South Australia
Yes. A variation is itself a domestic building work contract (section 3), so the contract rules in section 28 apply to it: in writing, all of its terms, legible, signed by both parties, and a copy to you as soon as practicable after it's signed. For contracts from 10/11/2025 the threshold is $20,000.
Tasmania
Yes, on a contract over $20,000. A variation needs a written variation document signed by both parties (sections 17–19); where it adds work, it has to be in place before that work begins. You get a copy within 5 business days (section 20).
Australian Capital Territory
The Building Act 2004 has no statutory rule for variations, so your building contract's variation clause governs. Get it in writing, priced, and signed by both of you before the work — which is what every state that does legislate asks for.
Northern Territory
The Building Act 1993 has no statutory variation rule either; the contract's variation clause governs. Same advice: in writing, priced, signed by both, before the work.
Sources
- Home Building Act 1989 (NSW): Schedule 2, Part 1, clauses 1(2), 1(3); sections 7, 7AA, 7AAA. Read 27/09/2026 and 07/10/2026.
- Domestic Building Contracts Act 1995 (Vic): sections 3, 37, 37(1), 37(2), 37(5), 38, 38(2), 38(3), 38(5), 38(8). Read 07/10/2026 and 08/10/2026.
- Queensland Building and Construction Commission Act 1991 (Qld): Schedule 1B, sections 1, 6, 7, 10, 40(2), 40(3), 40(5). Read 27/09/2026 and 07/10/2026.
- Home Building Contracts Act 1991 (WA): sections 7(1), 7(2). Read 27/09/2026.
- Building Work Contractors Act 1995 (SA): sections 3, 28. Read 27/09/2026.
- Residential Building Work Contracts and Dispute Resolution Act 2016 (Tas): sections 17 to 21, 17–19, 19, 20. Read 27/09/2026.
- Building Act 2004 (ACT): regulation 37. Read 27/09/2026.
- Building Act 1993 (NT): section 48B; regulations 41H, 41J. Read 27/09/2026.
- Home Building Regulation 2014 (NSW): clause 5. Read 07/10/2026.
- Domestic Building Contracts Regulations 2017 (Vic): regulation 6. Read 07/10/2026.
- QBCC Regulation 2018 (Qld): section 45. Read 07/10/2026.
Fill in the variation
- $9.90 to send it. Filling it in and the preview PDF are free.
- Both parties sign it. The other party signs from the link we email them, on a phone or a computer — no app, no account.
- Follows your state's rules. It asks for what your state requires and prints its statement, and the PDF ends with a signing record: who signed, when, and from which device.
See a signed example (PDF)A fictional job, signed by both parties.