Building Contracts in Australia: What to Check Before You Sign

A residential building contract is a legally binding document that can expose you to significant financial risk if you sign it without understanding what you are agreeing to — here is what to examine clause by clause before you commit.

Always get legal advice — but know what to look for

A building contract is one of the most consequential legal documents most homeowners will ever sign. For any residential contract over $20,000 in NSW (and at similar thresholds across other states), a solicitor review is strongly recommended — but arriving at that review with your own working knowledge of the key provisions puts you in a far stronger negotiating position. Familiarity with the contract also helps you ask the right questions during the build itself.

In Australia, residential building contracts are governed by a combination of state legislation, the National Construction Code (NCC), and industry-standard forms produced by bodies such as the HIA and Master Builders Australia. The contract you are handed may be a standard industry form, a heavily modified version of one, or a builder's own document. All deserve the same level of scrutiny.

Fixed price vs cost-plus

Fixed price (lump sum): The builder completes the agreed scope for the agreed price. Cost overruns are the builder's risk, not yours. This structure is strongly preferable for homeowners undertaking new builds or significant renovations. Be aware, however, that provisional sums (PS) and prime cost (PC) items create real exceptions to the "fixed" nature of the price — these are allowances for items not yet fully specified, such as engineered stone benchtops or engineered timber flooring. If the actual cost of those items exceeds the allowance, you pay the difference. Minimise their number and ensure each allowance is realistic.

Cost-plus: You pay the builder's actual costs plus a margin. The final total is genuinely unknown at signing. Cost-plus arrangements may suit highly complex or staged projects where full scope cannot be defined upfront, but they transfer almost all financial risk to you. Avoid them unless you have compelling reasons and a high degree of trust in the builder's record-keeping and transparency.

Progress payment schedule

The payment schedule must be tied to specific, verifiable construction milestones — not calendar dates. Paying ahead of completed work is one of the most common ways homeowners find themselves financially exposed if a builder becomes insolvent or abandons the site. As a general rule:

• The deposit should not exceed 5% of the contract price (10% is the statutory maximum in NSW for contracts under $20,000; 5% is typical and preferable above that threshold).
• Each milestone — base, frame, lock-up, fixing, practical completion — should be clearly defined so there is no ambiguity about when it is reached.
• The contract should include a process for raising a dispute about incomplete work before a progress payment is released.

Variations clause

A variation is any change to the agreed scope after signing — whether initiated by you or the builder. The clause governing variations should require that all variations are requested and approved in writing before work begins, priced at contract rates where applicable, and signed off by both parties. Verbal variations or a loosely drafted clause can allow a builder to claim additional costs after the fact, with little recourse available to you. If you are considering finishes such as engineered stone benchtops (indicative cost: around $680 per lineal metre) or upgraded cabinetry, locking those specifications in at contract stage — rather than leaving them as variations — protects your budget.

Rise and fall clause

A rise and fall (or escalation) clause allows the builder to pass on increases in materials or labour costs during the build. Structural steel, ready-mix concrete, and timber framing have all experienced price volatility in recent years, so builders increasingly seek to include this clause as standard.

For fixed-price contracts, push to exclude the clause entirely, or negotiate a cap — commonly 3–5% of the contract value — above which the builder absorbs further increases. An unlimited rise and fall clause in a fixed-price contract can effectively convert it into a cost-plus arrangement in all but name.

Completion date and delay penalties

The contract must state a specific completion date and a clear definition of practical completion. It should also include liquidated damages — a pre-agreed daily or weekly penalty payable by the builder for each day the project runs over time without a valid extension. Without liquidated damages, proving actual financial loss caused by a delay is difficult and expensive.

Review the extension of time (EOT) provisions carefully. Builder-friendly contracts often include broad EOT entitlements for weather days, homeowner decision delays, and supply chain issues. These are not inherently unreasonable, but the triggering conditions and notification requirements should be specific and time-limited.

Defects liability and statutory warranties

In NSW, the Home Building Act 1989 provides statutory warranties that apply regardless of what the contract says. Key protections include a six-year warranty for major defects and a two-year warranty for other defects, both running from the date of practical completion. The contract cannot validly exclude these rights, and any clause that attempts to do so should be flagged immediately with your solicitor.

Separately, the contract will typically include a defects liability period — usually six to twelve months post-practical completion — during which the builder must return to rectify defects at no cost to you. Confirm this obligation is explicit, and that the process for notifying defects is straightforward and in writing.

Termination provisions and builder insolvency

Understand what happens if the builder abandons the project, ceases to trade, or commits a material breach. The contract should give you clear, exercisable rights to terminate and engage a replacement builder, with the original contractor liable for any cost difference. In NSW, the Home Building Compensation Fund (HBCF) provides insurance cover for these scenarios for licensed builders on contracts over $20,000 — confirm that your builder holds current HBCF insurance before signing and that the certificate of insurance is attached to the contract.

Key clause checklist at a glance

Clause	What to look for	Red flag
Contract type	Fixed-price lump sum with minimal PS/PC items	Unlimited cost-plus or excessive provisional sums
Deposit	5% or less	Deposit above 5% before work commences
Progress payments	Milestone-linked, clearly defined	Date-based payments or vague milestones
Variations	Written approval required before work starts	Verbal variations permitted or no pricing mechanism
Rise and fall	Excluded or capped at 3–5%	Unlimited escalation on a fixed-price contract
Liquidated damages	Specific daily/weekly rate for overrun	No delay penalty or nil rate inserted
Defects warranty	Statutory rights preserved; clear rectification process	Clause purporting to limit statutory warranties
Termination and insurance	Clear rights; HBCF certificate attached	No insolvency provision; no insurance confirmation

This article is for general information only and does not constitute legal advice. Always consult a solicitor before signing a building contract.

Before you reach the contract stage, use the DesignBuildSource cost calculator to establish a realistic budget baseline for your project — then cross-check the contract price and any provisional sum allowances against those figures. If you are still selecting a builder, the professional directory lists licensed contractors by suburb with verified credentials.