Fixed Price Building Contracts in NSW: What’s Actually Included

The phrase fixed-price contract is used by every builder advertising in Western Sydney. The actual document behind it varies enormously. Some are truly fixed, signed and delivered at the same price. Others are riddled with escalation clauses that let the builder push the price up freely once you are locked in. This guide walks through what a real fixed-price contract should look like.

The fundamental promise

A fixed-price building contract means: the contract sum stated at signing is what you pay at handover. The two narrow exceptions are:

• Variations you request and approve.
• Specific events explicitly named in the contract that trigger a price adjustment (e.g., unforeseen rock excavation, council requiring an extra stormwater treatment).

Anything else, the builder cannot change the price without your consent.

What a true fixed-price contract contains

• Contract sum stated clearly in dollars, GST inclusive.
• Scope of works defined by reference to architectural drawings, specifications and inclusions list, all attached.
• Inclusions list as a separate signed document. This is the line-by-line spec.
• Variation procedure requiring written quote and signed approval before work proceeds.
• Progress payment schedule tied to defined stages (deposit, slab, frame, lockup, fitout, handover) with dollar amounts.
• Provisional sums and PC sums listed individually with allowances, and explicit language that any over- or under-spend is reconciled at completion.
• Special conditions covering specific exclusions, site condition assumptions, and any builder-specific clauses.
• Building period in calendar days, with extension triggers listed (e.g., adverse weather).
• Liquidated damages per day if builder is late beyond the building period.
• Home Owners Warranty insurance certificate attached.
• NSW Office of Fair Trading dispute resolution clauses.

What is not a fixed-price contract

Watch for these phrasings that mean the contract is open to escalation:

• “Price subject to soil test results.” If the soil test has not been done, the contract is not fixed. Do the soil test first, then sign.
• “Allowance for site costs.” If site costs are an allowance, not a fixed amount, you wear the variance.
• “Subject to council requirements.” Council requirements should be known at signing. Anything beyond should be a small named contingency.
• “Rise and fall clause” or “cost escalation clause” outside of NSW Special Condition framework. Beware.
• Open-ended provisional sums for major items. A $40,000 provisional for kitchen is a recipe for a $60,000 actual.

The legitimate variation triggers

Some variations are not the builder’s fault and they should not eat the cost. Examples:

• Genuine unforeseen rock excavation, where soil test showed clay or sand but rock is encountered at excavation. The contract should specify a dollar per cubic metre rate.
• Council requirement for stormwater detention not previously required, e.g. a new council policy in mid-build.
• Owner-requested variations: facade change, tile upgrade, window addition.
• Statutory authority requirements: ESS gas connection forcing a different gas meter location, etc.

For each trigger, the contract should specify either a dollar rate (e.g., rock at $120 per cubic metre) or a quote-and-approve procedure before work proceeds.

The 2022 market disruption clause

After the 2022 building material cost shock (timber prices doubled, steel up 40 percent), many NSW builders inserted Special Condition clauses allowing renegotiation under extraordinary market conditions. These clauses are typically narrow: they require evidence of a market-wide cost increase of over X percent during the build period, and apply only to specific named materials.

These clauses are reasonable in 2024 because the building industry was genuinely affected, but they should be narrow. A clause that gives the builder unilateral right to increase price for any reason is unreasonable.

Progress payment schedule, the right way

Standard NSW progress payment milestones:

• Deposit: 5 percent (legal maximum at contract signing in NSW). Builders sometimes try to charge more. Refuse.
• Slab complete: 15 to 17 percent.
• Frame complete: 20 to 22 percent.
• Lockup (brick, roof, windows in): 20 to 22 percent.
• Fitout complete (kitchen, bathrooms, painting): 25 to 27 percent.
• Handover: remaining balance (typically 7 to 12 percent).

Total adds to 100 percent. Beware contracts where 90 percent is paid before fitout is complete, which leaves you no leverage if defects emerge.

What to do if your contract has weak fixed-price language

Negotiate. Builders expect this. Specific changes you should ask for:

• Convert provisional sums into fixed amounts where possible.
• Cap variation administration fees.
• Require written approval before any work over $500 in scope variation.
• Tighten Special Condition triggers (specific percentage, specific materials, specific timeframe).
• Confirm timeline extension triggers are specific (e.g., 1.5 days per adverse weather day, evidenced by Bureau of Meteorology data).

Final advice

A fixed-price contract is only as good as the inclusions list it references and the discipline of both parties to stick to the agreed scope. The most expensive variations we have ever administered have all been owner-driven late changes, not builder-driven. Lock in your selections before contract, resist changes during build, and the fixed-price promise will hold.