A variation is a change to the work the contract describes, and an extension of time (EOT) is a later date for completion granted because of a delay the contract allows you to claim for. Both are contractual rights, not automatic ones: you usually have to follow the contract’s procedure, in writing and within its deadlines, or risk losing the money or the time.
On commercial jobs that means reading the variation and EOT clauses in your contract, such as AS 4000 or AS 2124, and meeting every notice requirement. On home building jobs, state laws add their own rules: in NSW, Victoria and Queensland, variations generally must be agreed in writing, and in most cases before the work is done. This guide explains how it works in general terms. For a live claim, get legal advice on your contract.
What is a variation in a building contract?
A variation is any change to the scope of work after the contract is signed. It can add work, take work out, or change how, where or with what materials the work is done. Variations arise when:
- the owner or principal asks for a change, such as a different finish or an extra room
- the design changes, for example when drawings are revised or a consultant issues a new detail
- the site turns out to be different, such as unexpected rock or contamination, if the contract treats that as a variation or a latent condition
- a building surveyor, certifier or authority requires a change to comply with the law.
Who can direct a variation and how is it valued?
Standard form contracts give the principal, or the superintendent acting for them, the power to direct variations, and set out how the price of a variation is worked out. AS 4000-1997, for example, values a variation by prior agreement first, then applicable rates or prices in the contract, then rates in any priced schedule, and finally reasonable rates or prices including a reasonable amount for profit and overheads. A contractor generally cannot vary the work on its own initiative and then expect to be paid for it.
The release announcing AS 4000:2025 says the new edition keeps the risk allocation of the 1997 edition. Commentary on the 2025 edition notes that variations are effective only where directed in writing before practical completion, so check the edition and any special conditions in your contract.
What is an extension of time and when can you claim one?
An extension of time moves the date for practical completion because of a delay. It matters for two reasons. First, it protects you from liquidated damages, the fixed daily amount many contracts let the principal deduct for late completion. Second, it may open the door to delay costs, if the contract allows them.
Most contracts only allow an EOT for a “qualifying cause of delay”. These are usually events outside the contractor’s control or caused by the principal, such as:
- variations directed by the principal or superintendent
- late access to the site, late information or late approvals from the principal
- inclement weather beyond what the contract allows for
- industrial action or other events listed in the contract.
The delay generally has to affect the critical path, meaning it actually pushes back the completion date, not just one activity that has float.
What are notice time bars and why do they matter?
A time bar is a clause that says you lose your entitlement if you do not give notice, or make a claim, within a set time. They are common in both variation and EOT clauses, and courts in Australia have often enforced them.
Under the 1997 edition of AS 4000, the contractor’s written EOT claim is widely understood to be due within 28 days of when it should reasonably have become aware of the cause of delay, and AS 2124-1992 also uses a 28-day period. Many principals amend these periods, sometimes shortening them, so always read the special conditions. Commentary on AS 4000:2025 indicates that some fixed periods were replaced with “as soon as reasonably practicable”, which is less certain, not more generous.
Residential contracts published by industry associations, such as HIA and Master Builders contracts, also contain notice requirements for delays and variations, often with short periods.
What records do you need for delay and disruption claims?
Claims for time and money are won and lost on records made at the time. A superintendent, adjudicator or court will give far more weight to a dated site diary entry than to a reconstruction prepared months later.
Keep these records from day one:
- A baseline program agreed at the start, then regular updates showing actual progress against it.
- Daily site diaries recording weather, labour and plant on site, work done, visitors, instructions received and anything that stopped or slowed work.
- Dated photos and videos, ideally showing the same areas at regular intervals.
- Written instructions and requests for information (RFIs), with the date sent and the date answered.
- Notices of delay and claims, sent in the way the contract requires and to the right person.
- Cost records that separate the extra labour, plant, materials and supervision caused by the delay or variation.
Disruption, where work takes longer or costs more because it was interrupted even though completion is not delayed, is harder to prove. It usually needs a comparison between productivity in affected and unaffected periods, which is impossible without good daily records.
What are the home building variation rules in each state?
On residential jobs for home owners, state home building laws impose their own variation rules on top of the contract.
- NSW: contracts for residential building work over $20,000 must contain a clause stating that any agreement to vary the contract or the plans and specifications forms part of the contract and must be in writing and signed by both the home owner and the contractor. NSW Government guidance for consumers notes an exception where urgent work is needed because of a likely danger to a person or damage to property, in which case the variation can be recorded in writing after the work.
- Victoria: under the current Domestic Building Contracts Act 1995 rules, Consumer Affairs Victoria says the builder and client must agree in writing and put the details, including the new price and completion date, into the contract before the work is carried out, using a variation notice. A notice is not required where the builder reasonably believes the change will not require a permit change, will not cause delay and will not add more than 2% to the original contract price. The client should not have to pay for variations caused by issues the builder should have identified before starting work.
- Queensland: the QBCC says that, before starting variation work on a domestic building contract, the contractor must present the variation to the home owner in writing and the owner must agree in writing. The document must describe the variation, give the date of the request, estimate any delay and state the change to the price. The contractor must give the owner a copy before the variation work starts or within 5 business days of agreement, whichever is first, and cannot require payment before the variation work starts.
Victoria is changing its rules. The Domestic Building Contracts Amendment Act 2025 will introduce a single variation process for major domestic building contracts, whether the owner or the builder asks for the change. It was due to start by 1 December 2026, and Parliament has since passed a change moving the date to 31 March 2027, so check the current position before you update your templates. A variation can also affect home warranty insurance, so read our guide to statutory warranties and home warranty insurance.
How do variation and EOT claims link to security of payment?
Once a variation is approved and priced, it is claimed through your normal progress claims. Where the contract allows it, delay costs that flow from an EOT can be claimed the same way. If the claim is disputed, security of payment laws give you a fast route to adjudication. Our guide to security of payment in each state explains the deadlines.
Two points matter here:
- Adjudicators look at the contract. If you missed a notice or time bar, the respondent will say so in its payment schedule, and the adjudicator may agree. Good records and compliant notices are what make a variation claim succeed.
- Victoria’s rules changed in 2026. Before 15 April 2026, Victoria’s Act excluded many disputed variations and delay costs from the SOP process. Those “excluded amounts” have been repealed, so these claims can now be made through the Act, subject to the contract.
In Queensland, a variation that lifts the contract price by at least 30% can also bring a contract into the project trust account regime part-way through, so check eligibility after large variations.
Checklist: claiming variations and EOTs properly
- Read the variation, EOT, notice and liquidated damages clauses before work starts, including every special condition. Our guide to building contract basics covers what to check first.
- Diarise every notice period in the contract, and the person and method for giving notice.
- Never start varied work on a verbal instruction unless it is a genuine emergency; get a written direction or a signed variation first.
- On home building jobs, follow your state’s written variation rules, including the copy-to-owner requirements in Queensland.
- Give notice of a delay as soon as you become aware of it, even if you cannot yet say how long it will last. Update it as the delay develops.
- Keep daily records: diary, photos, program updates, RFIs and the extra costs.
- Price and claim variations promptly in your next progress claim, with the supporting evidence attached.
- Get legal advice if a claim is rejected for being late or if the contract’s notice clauses are unclear.
Claim every dollar and day you are owed
CPD-accredited online courses on contract administration, variations, extensions of time and getting paid, each with an assessment and a certificate.
- Contract Administration: Variations, Claims and Extensions of Time View course →
- Security of Payment and Getting Paid in Construction View course →
- Basic Contract Law for Building and Construction View course →
- Managing Risk and Reducing Disputes in Construction View course →
- Home Building Law, Statutory Warranties and Home Warranty Insurance View course →
Frequently asked questions
Can I be paid for a variation that was only agreed verbally?
Sometimes, but it is risky. On commercial jobs it depends on the contract and the circumstances. On home building jobs in NSW, Victoria and Queensland, the law generally requires variations to be in writing, and failing to follow those rules can limit what you can recover. Always get the variation in writing before the work starts.
What is a qualifying cause of delay?
It is a delay event that the contract says entitles you to an extension of time. Common examples are variations, late access or information from the principal, inclement weather beyond the allowance in the contract, and other events specifically listed. Delays caused by the contractor are generally not qualifying causes.
What happens if I miss the deadline to claim an extension of time?
Under many contracts, a late claim means you lose the entitlement to that extension, which can expose you to liquidated damages. Some contracts give the superintendent power to grant an extension anyway, and in Victoria a time bar may be declared unfair in limited circumstances, but you should not rely on either.
Does an extension of time mean I get paid for the delay?
Not automatically. An extension of time protects you from liquidated damages for that period. Whether you can also recover delay costs depends on the contract, which often allows them only for certain causes of delay, such as delays caused by the principal.
Do the same variation rules apply to commercial and residential jobs?
No. Commercial jobs are governed mainly by the contract. Residential jobs for home owners must also comply with state home building laws, which set minimum requirements such as written, signed variations and, in some states, rules on when you can ask for payment.
Is AS 4000-1997 still used?
Yes. Many existing contracts and some new ones still use the 1997 edition or amended versions of it. Standards Australia published AS 4000:2025 in June 2025, and clause wording and numbering can differ between editions, so always check which edition your contract uses.
Sources and further reading
- Standards Australia — AS 4000:2025 General Conditions of Contract (news release, 30 June 2025)
- Standards Australia Store — AS 4000:2025 General Conditions of Contract
- Victorian Legislation — Building and Construction Industry Security of Payment Act 2002, s 13A notice-based time bar provisions
- NSW Government — Guide to providing home building contracts
- Consumer Affairs Victoria — Changing a domestic building contract price
- Consumer Affairs Victoria — New domestic building contract laws passed in Victoria
- QBCC — Contract changes and variations
- NSW Government — Making a payment claim under Security of Payment laws