How to write a building variation that gets signed and paid (NSW rules included)

Ask any experienced builder where jobs go wrong and most will say the same thing: variations. Not because variations are unusual, since almost every residential job has them, but because they are so often handled badly. A change agreed on site, a price mentioned in passing, a bill at the end of the job that the owner does not remember agreeing to. That is how a good relationship becomes a dispute.

The fix is not complicated. It is discipline: every change written down, priced with workings, signed before the work starts. This guide explains what a variation is, what NSW requires, and how to write variations that get signed and paid.

What a variation is, and what it is not

A variation is a change to the work described in the contract. The owner wants a different window, an extra power point, a moved wall, an upgraded finish. The certifier or an authority requires a change. A condition on site, such as rock or an unknown service, means the work must be done differently.

A variation is not:

• A correction of the builder’s own mistake. If the work has to be changed because it was built wrong, that is the builder’s cost.
• A general price increase. If materials or labour cost more for the same work, that is a pricing risk. Whether any of it can be passed on depends on the contract, not on the variation clause.
• Something already included. If the contract and plans already require it, charging for it as a variation is not legitimate.

Getting that distinction right matters. Trying to recover a mistake or a cost increase through a variation is one of the fastest ways to lose an owner’s trust, and it will not survive scrutiny in a dispute.

What NSW requires

In NSW, residential building work is governed by the Home Building Act 1989. Building Commission NSW summarises the key points for variations in its consumer guidance:

• In writing. All contracts for work valued above $5,000 must be in writing, and variations to that contract must also be agreed in writing before the work is carried out.
• Signed and attached. The variation should be signed by both the owner and the contracting builder or tradesperson (or their nominated supervisor or agent), and attached to the contract.
• Cost implications explained. Documents authorising variations must contain a statement explaining the cost implications of the variation and its impact on the overall contract price. The calculation of the price change should be shown, rather than just a simple dollar amount.
• Builder’s fault. If the reason for a variation is the builder’s or tradesperson’s fault, the owner does not have to pay for the extra work to fix the problem.

The Commission also advises owners to agree all work in writing regardless of value, to review any variation carefully, and to agree only if the work itself is changing. Builders should assume that owners are reading that advice.

The anatomy of a good variation

The description is where most variations fail. “Extra electrical work” is not a description. “Supply and install four additional double power points on the north wall of the living room, as marked on drawing A-102 revision C” is. The test is whether a stranger, reading the variation a year later, would know exactly what was changed.

The price is the second failure point. A single dollar figure invites the question “how did you get that?”. Showing labour hours and rate, materials, subcontractor quotes, margin and GST answers the question before it is asked, and in NSW it is what the regulator expects.

The third is time. Many variations add days to the programme, and those days matter if the contract has a completion date and liquidated damages. If a variation adds time, say so in the variation, and have the owner sign it. A variation that is silent on time can leave the builder carrying the delay.

The process

The single most important habit is not starting the work until the variation is signed. It is tempting, on a busy site with an owner standing next to you asking for a change, to just do it and sort out the paperwork later. Later is when the owner does not remember agreeing, disputes the price, or refuses to pay because the variation was never signed. A two-day delay to get a signature is always cheaper than a dispute.

Where the owner is hard to reach, a variation can often be signed electronically. Many builders now send variations from their project management software or a simple PDF form for e-signature, which removes the excuse that the paperwork was too hard to get signed.

Who pays for which changes

Certifier and authority requirements are a common grey area. If a certifier requires a change because the design did not comply, the question is whether that was the builder’s responsibility under the contract (for example, in a design and construct arrangement) or the owner’s designer’s. If an authority introduces a new requirement after the contract was signed, the contract may treat that differently again. The answer is in the contract, so read it before you write the variation.

Latent conditions, such as rock in an excavation, contaminated soil or an unmapped service, are usually dealt with by a specific clause that sets out how and when the builder must notify the owner. Missing the notice requirement can cost the builder the right to claim, so notify promptly and in writing, then follow with a variation.

Keep a register

On a job with more than a couple of variations, a simple register prevents confusion. It shows every variation, its status, its price and time effect, and whether it has been invoiced. It also makes progress claims and the final account easier, and it is the first thing anyone will ask for in a dispute.

Pricing variations fairly

Variations are often priced at a premium, and owners know it. There are legitimate reasons a variation costs more than the same work would have cost at tender: small quantities, disruption to the programme, re-ordering, and work done out of sequence. But a variation priced far above the value of the work damages trust and invites challenge.

A fair variation price is the real cost of the change, including disruption, plus the margin the contract allows. If you show the calculation, a fair price is easy to defend. If the price cannot be defended with workings, it is probably not fair.

Credits for deleted work

Variations are not always additions. When the owner removes something from the scope, the contract price should reduce by a fair credit. Owners are understandably sensitive when additions are priced generously and deletions are credited meanly. Treat credits the same way as additions: show the calculation, including any costs already incurred, such as materials ordered or work done that cannot be reversed.

Common variation disputes, and how to avoid them

• “I never agreed to that.” Avoided by a signed variation before the work.
• “That price is outrageous.” Avoided by showing the calculation and pricing fairly.
• “Why is the job late?” Avoided by stating the time effect in each variation.
• “That was already included.” Avoided by checking the contract, plans and specification before issuing the variation.
• “You made that mistake, why am I paying?” Avoided by not issuing variations for your own errors.
• “I didn’t know it would affect the insurance.” Avoided by including any HBCF premium change in the variation.

Variations and progress claims

Variations are usually claimed with the next progress payment after the work is done, or as the contract specifies. Include each variation separately on the claim, with its number, so the owner can match it to what they signed. Unsigned variations should not be claimed as if they were agreed. If there is a dispute about a variation, deal with it separately rather than letting it hold up the whole progress claim.

Variations and extensions of time

A variation changes the work. An extension of time changes the completion date. They often go together, but they are separate contractual mechanisms with their own rules. Most residential contracts allow the builder to claim an extension of time for delays caused by variations, among other causes, but many require the claim to be made in writing within a set period after the builder becomes aware of the delay.

The simplest approach is to deal with time in the variation itself, as described above, so the owner signs off on the time and the cost together. Where the delay only becomes clear later, lodge a separate extension of time claim promptly, as the contract requires. Missing the notice period can leave the builder liable for delay damages even though the delay was caused by the owner’s own changes.

When the owner will not sign

Sometimes an owner wants the change but will not sign the variation, usually because they dispute the price. Doing the work anyway is the worst option: it leaves the builder with no signed agreement and a disputed claim. Better options, depending on the contract and the situation, include:

• Explaining the calculation in person and offering to review it line by line.
• Offering to proceed without the change, as the contract originally required.
• Getting an independent quote for the varied work to show the price is fair.
• Using the contract’s dispute resolution process, or the free services available through NSW Fair Trading and Building Commission NSW, if a genuine disagreement cannot be resolved.

If the change is required, for example by the certifier or an authority, and the work cannot wait, record the instruction and your notice to the owner in writing, and seek advice on your contractual position before proceeding.

Records that make variations stick

A signed variation is strongest when it is supported by other records: the site diary entry noting the owner’s request, photos of the work before and after, supplier invoices for materials, and the correspondence where the change was discussed. Stored together in the job file, those records turn a potential argument into a simple matter of evidence.

A note on small jobs

On small jobs, variations are often agreed verbally because the paperwork feels out of proportion. That is exactly where disputes about a few hundred dollars can grow into complaints to the regulator. A short, signed variation on one page takes five minutes and removes the argument. For NSW contracts over $5,000, the written requirement applies regardless.

Train the people who say yes

On many jobs, variations are agreed not by the builder but by a supervisor or a trade standing next to the owner. Make sure everyone on site knows the rule: no change is agreed until it is written, priced and signed. Give supervisors a simple variation form, or an app, and the authority to say “I’ll get that priced for you” rather than “no worries, we’ll do it”.

The bottom line

Variations are not a problem. Unwritten, unpriced, unsigned variations are. Write every change down, show how you priced it, state what it does to the programme, get it signed before you start, and keep a register. It is the cheapest insurance a builder can buy.

Questions builders ask

• Contracts
• Dispute resolution
• Home Building Act
• Variations

Published 8 August 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.