Variations in construction: how to price them and get them approved
By Bailey Holdsworth, founder
26 August 2026 · 8 min read
A variation is a scope change after the price is set: a client request, a site condition or an engineer's direction. Price it like a small quote (labour, materials, disruption, margin) and get a written yes with the price and time impact before you start. NSW, Victoria, Queensland and WA require written variations on home building contracts above their thresholds.
Every job has one. The client wants the deck a metre longer, the engineer wants a bigger beam, the ground turns out to be rock. Price it and get a written yes before you start and it is a variation you get paid for. Just do it and it is a gift. Here is how to tell the difference, price one, get it approved and get it onto the invoice.
What counts as a variation
A variation is a change to the work after the price is agreed. The quote described a scope, the client accepted it, and now something is different. It can come from the client, the site, or someone with authority over the job.
- The client changes their mind: a bigger pergola, a different tile, a second power point in every room
- The site is not what the plans showed: rock where the footings go, rot in the bearers, a slab that needs more fill
- Someone with authority directs a change: the engineer, the building surveyor, the certifier or the council
- Something the client was supplying turns up late, or wrong, or not at all
What is not a variation is anything that was already part of the described job. If your quote said supply and install the kitchen and you forgot the kickboards, that is a take-off mistake and the cost is yours. So is rework on your own errors. Our guide on quote vs estimate covers why an accepted quote fixes the price for the scope you wrote down.
Why unapproved variations kill margin
Plenty of variations never get refused. They get done, at cost or for nothing, because you were already there and it was easier to say yes than to stop and write it up. That habit is a common margin leak, and our guide on why your jobs are not as profitable as you think covers it for that reason.
The maths is brutal. A job quoted with a 10% net margin has $1,400 of profit in every $14,000. One unbilled extra that cost you $600 takes nearly half of it. A second takes the rest. The job still looks fine on paper, because the quote and the invoice match, but the money is gone.
Variations bleed margin in three ways:
- You did the work and never priced it. The client got it free
- You priced it after the fact. Now it is an argument on the final invoice, and the whole claim is held up
- You priced the labour and materials but not the disruption: the extra trip, the crew waiting on a decision
How to price one
Price a variation the way you price a job, just smaller. Same cost rates, same margin, same rules. The method in how to quote a carpentry job works for a $600 variation as well as a $60,000 build. Four parts:
- Labour at your true hourly cost, with super, leave, insurance and the unbillable hours in it, not your bare wage. Count the hours honestly: a change mid-job takes longer than the same work on a clean run
- Materials at today's price from your supplier, plus delivery or the pick-up trip
- Disruption, the part that is easiest to forget: extra trips, waiting on a decision, pulling apart something already done, the day the next trade cannot start. If it costs you a day, price a day
- Margin on top, the same way as the main quote. Divide your total cost by one minus your target margin: for 20%, divide by 0.8
Pricing a $1,200 variation: a privacy screen added to a deck (example numbers)
- Materials: screening, posts and fixings
- $400
- Labour: 6 hours at a true cost of $80 an hour
- $480
- Disruption: an extra supplier trip, 1 hour
- $80
- Total cost
- $960
- Divide by 0.8 for a 20% margin
- $1,200 ex GST
- Add 10% GST
- $1,320 inc GST
Quote the variation at $1,200 ex GST ($1,320 inc GST). Do it on a nod for $960 and the job just lost $240 of margin. Do it for nothing and it lost $960.
Two more rules. Do not discount variations: they usually carry more risk than the base job and nobody is quoting against you. And price the time impact too, because extra days move the completion date and every stage after it.
Get it in writing before you start
The price is only half of it. A variation you cannot prove was agreed may not get paid. Before you start, the record needs:
- The job or contract it belongs to and a variation number, so the invoice can reference it
- A plain description of the change and why: client request, site condition, or a direction from the engineer or certifier
- The price ex GST and inc GST with the make-up shown, or the method if it is time and materials
- The time impact: extra days on site and the new completion date, even if the answer is none
- When it is payable: with the next progress claim, when the variation is done, or on the final invoice
- The client's acceptance: a signature, or a written yes by email or text, and the date
On a small job, an email or a text the client replies to is fine. Above your state's written-contract threshold, use the variation clause or form in the contract itself. And if the client will not put it in writing, do not do the work. Say it kindly and early: happy to do it, I just need a yes in writing before I order the timber.
The rules by state
Each of the states below has its own home building contract law, and above a set contract value it says how variations must be handled. These are the rules we checked against the regulator's page or the legislation. If your state is not listed, check with your building regulator first.
| State | What the rules say |
|---|---|
| NSW | a written contract is required when the contract price is over $5,000 including GST, under the Home Building Act 1989. The NSW Government's guidance says variations must be in writing, attached to the contract and signed by both the owner and the contractor (or their nominated supervisor or agent), with a statement explaining the cost implications and impact on the overall contract price, and the calculation shown rather than just a dollar amount. Where a variation is needed because of likely danger to someone or damage to property, it may be put in writing after the work |
| Victoria | a major domestic building contract is required for most work worth more than $10,000, under the Domestic Building Contracts Act 1995. Consumer Affairs Victoria says builder and client must agree in writing to the changes and put the details, including the new price and completion date, in the contract before the work is carried out. A variation notice is not required when the client asks for the change and the builder reasonably believes it will not require a change to any permits, cause delay, or add more than two per cent to the original contract price |
| Queensland | a written contract is required for domestic building work priced over $3,300 including labour, materials and GST, complying with Schedule 1B of the QBCC Act. The QBCC says the contractor must present the variation in writing before the variation work starts or five business days from the day both parties agree, whichever comes first, and the home owner must agree in writing. The document must describe the variation, state the date of the request, estimate any delay, and state the change to the contract price (or how it will be worked out) and when it is to be paid. The only exception is urgent work where a written copy first is not reasonably practicable, and you cannot require payment before the variation work is started |
| Western Australia | the Home Building Contracts Act 1991 sets minimum contracting terms for fixed-price contracts between home owners and builders valued between $7,500 and $500,000. Section 7 says a variation must be in writing, setting out all of its terms and its cost and showing its date, signed by the builder and the owner or their respective agents, and the owner must be given a copy of the signed variation as soon as reasonably practicable after signing and before the work it relates to is commenced |
Summary of the state rules cited in the sources below. Check your own state's page before relying on a figure.
Notice the pattern: writing, a price, a date and both parties' agreement, before the work starts. The record above gives you all four.
Invoicing variations with your progress claims
An approved variation still has to land on an invoice. On a staged job, claim it with the stage it was done in, but as its own line: 'Stage 3: lock-up, $16,000' and underneath it 'Variation 2: privacy screen, $1,200'. Roll it into the stage total and you invite a dispute on the whole claim instead of just the extra. Our guide on progress claims and payment stages covers the stage side.
- Reference the variation number and the acceptance date on the invoice line
- Claim it when it is done, not at the end of the job. Small amounts left to the final invoice are easy to argue down
- A variation changes the contract sum, so update any later stage sized as a percentage of the total and show the new total
- If you are registered for GST, show GST on the variation line like every other line on the tax invoice
Track them where the job lives
Variations go unbilled because the change was agreed on site at three on a Tuesday, in a text or a conversation, and by the time the invoice is written it is a memory. The fix is to log it where the job's numbers live, the day it is agreed.
That is how TrackYaTradie handles it: you add a variation against the job with its description, price and status, and it carries through to the progress claim and the invoice, so nothing falls through the gap between site and office. Run your last job through the job profit calculator and add back the extras you did for free to see what that gap cost you. See how it fits a staged build in built for builders, or a slab job with one big variation in built for concreters.
Questions
Can I charge for a variation the client asked for verbally?+
You can ask, and a client who asked for the work will often pay without fuss. But a verbal request is hard to prove if they do not, and on home building contracts above your state's written-contract threshold the law expects variations to be in writing before the work starts. The safe habit is to answer the verbal request with a text or email that sets out the change, the price and the time impact, and ask for a written yes before you start. That turns a conversation into a record in two minutes.
What if the client refuses to sign?+
Do not do the work. A client who will not put their name to a price before the work has told you how the conversation about paying for it will go. Explain that the written yes protects them as much as you, because it fixes the price. If the change is something the job cannot proceed without, such as a site condition, put it in writing to them anyway, with the price and what happens if it is not done, so there is a record of what you told them and when. Then check your contract and your state's rules before going further.
Is a variation the same as a change order?+
Same thing, different word. Change order is the term you will often hear on commercial projects and in software built overseas. Australian home building law and the state regulators say variation. Whatever you call it, it is a documented change to the agreed scope with a price, a time impact and the client's acceptance.
Do variations need GST?+
If you are registered for GST, yes. The ATO describes GST as a broad-based tax of 10% on most goods, services and other items sold or consumed in Australia, and its tax invoice rule is that if a customer asks for a tax invoice you must provide one within 28 days, unless the sale is $82.50 (including GST) or less. A variation is part of the same building work as the rest of the job, so price it ex GST, show the inc GST figure on the variation record, and put it on the tax invoice with GST like every other line.