Variation mistakes that cost you margin

Variations should add margin. On a lot of jobs they take it away instead, because the extra gets built and the money never follows. These are the mistakes that come up again and again in our sources, with the fix for each.

1. Saying yes on site

A customer asks the carpenter for something extra, the carpenter says “no worries”, and the work is done before the office hears about it. A Sydney builder did a $160,000 basement excavation variation without written approval and never got paid for it.¹ He now minutes every customer meeting by email, costs variations within two to three days, and nothing proceeds without written sign off.

Do this instead: make it a site rule that supervisors and trades log requests and never agree them. The office prices, the customer signs, then the work starts.

2. Leaving the price until the end of the job

When variations are added up at final invoice, the customer has forgotten half of them and argues the rest. The Professional Builder lists variations as one of the four places margin leaks after a job starts, alongside labour, materials and subbies, and the fix it gives is to price them in real time and get them signed off as you go.²

Do this instead: price every variation within the week, and bill it on the next claim or invoice.

3. Being too nice

Builders tend to please people. A New Zealand builder who builds on remote islands recalled another builder invoicing about $70,000 of a roughly $120,000 variation, because the full bill felt like too much to send.³ He agreed that builders lean towards absorbing variations and free work.

Do this instead: price every variation in full and send it. If you decide to give something away, make that call in the office, in writing, so it is a choice and not a habit.

4. Writing a vague scope

You can only vary something that was defined in the first place. A variation exists relative to the baseline scope, and progress claims are measured against it too. Leaving an item out of the scope is not the same as excluding it, and an unclear scope is usually read against whoever drafted it, which in residential building is normally the builder.⁴

Do this instead: write stated exclusions into the scope. “Excludes driveway and landscaping” settles more arguments than saying nothing about them.

5. Ignoring the small ones

A small extra feels like it is not worth the paperwork. A Western Australian refurbishment business found variations were being missed until it set a process: the supervisor logs the request, it is priced in the software, the customer approves it, then it is done. The amounts were a couple of thousand dollars each, but they added up across 40 jobs.⁵

Do this instead: run every variation through the same process, whatever the size. Mobile sign off keeps the small ones quick.

6. Forgetting the customer’s lender

On a financed job, a variation can change stage amounts and the valuation. A finance broker uses the example of a $15,000 tapware upgrade at stage 2. If the customer cannot cover the difference, the bank may stall the next draw, and your claim waits.⁶

Do this instead: before you issue a variation on a financed job, confirm where the money is coming from and tell the broker or lender.

7. Assuming the rules are the same in every state

Variation rules come from state law and your contract, and they differ. In Victoria, the Consumer Legislation Amendment Bill 2026 was introduced into Parliament in June 2026. It proposes a criminal offence for undocumented variation agreements where the contract is worth $20,000 or more, or where a variation adds $5,000 or more.⁷ At the time of writing it is a bill, not law. Other states have their own rules on written variations, so check the domestic building legislation where you build.

Do this instead: document every variation in writing in every state, whatever your local minimum is. Then a rule change does not catch you out.

The numbers behind it

What happened	Amount	Where
Basement excavation variation, no written sign off, never paid	$160,000	NSW
Variation invoiced well below its value	About $70,000 of $120,000	NZ
Missed small extras	A couple of thousand dollars each, across 40 jobs	WA
Variation that can stall a bank draw	$15,000 tapware upgrade	General
Proposed Victorian thresholds for the offence	Contract $20,000+, or variation adding $5,000+	VIC (bill, not law)

If it is not written down and signed, treat it as work you are doing for free.

This is general information, not legal advice. Check your contract and your state’s rules, and talk to a construction lawyer if you are unsure.

Where to next

For the step by step process that prevents most of these, read How to price a variation. If your scope keeps causing arguments, start earlier with Contract mistakes builders make before they sign.

Footnotes

1. Joshua Rosinski, “How Outsourcing Administration Cut Overheads From 35% To 8%”, The Professional Builder (podcast), 2026. https://www.youtube.com/watch?v=vTe7JnQx6fg ↩

2. “Why Dropping Your Margin By 1% Costs You 16 Days Of LEAVE”, The Professional Builder (podcast), 2026. https://www.youtube.com/watch?v=kwUyPAcIquc ↩

3. Matt Garlick, “Remote Island Builder Specialist”, Better Builder Podcast, 2026. https://www.youtube.com/watch?v=K6VFjQKSJV4 ↩

4. “The Scope of Works Is the Document Your Statutory Warranty Attaches To. Most Builders Treat It as Paperwork.”, The Good Builder, 2026. https://thegoodbuilder.com.au/the-scope-of-works-is-the-document-your-statutory-warranty-attaches-to-most-builders-treat-it-as-paperwork/ ↩

5. Simone McKenzie, “If You Treat Your Staff Like THIS, You Will Lose Everything”, The Professional Builder (podcast), 2026. https://www.youtube.com/watch?v=3-xRfhpZnyA ↩

6. “‘Money Talks, Wealth Whispers’: What Builders Can Learn From Finance Broker Barry Wilkinson”, The Good Builder, 2025. https://thegoodbuilder.com.au/money-talks-wealth-whispers-what-builders-can-learn-from-finance-broker-barry-wilkinson/ ↩

7. “Pricing and Estimating for Australian Builders”, The Good Builder, 2026. https://thegoodbuilder.com.au/pricing-and-estimating-for-australian-builders/ ↩