What to Look for in a Custom Home Building Contract
Your custom home building contract is the document that protects your money, your timeline, and your finished home, so it deserves more than a quick skim before signing. The good news is that a sound contract follows a predictable shape, and once you know what to look for, the red flags stand out quickly.
Quick answer: A custom home building contract should clearly set out the fixed price, a realistic building schedule, staged progress payments tied to completed work, how variations are priced, and the warranties and domestic building insurance protecting you. Before signing, check the deposit, the provisional sums, and that the builder is VBA-registered.
What a custom home building contract must include
For a project of this size you will usually sign a major domestic building contract, often an industry standard such as an HIA building contract in Victoria, or a similar Master Builders form. Whatever the template, these are the clauses to read carefully.
The parties and the builder's registration
The contract should name the registered building company and its registration details. Builders in Victoria must be registered with the Victorian Building Authority (VBA), so confirm the registration is current and matches the entity you are contracting with.
The fixed contract price and what it includes
A good contract states a clear price and, just as importantly, what is and is not included. Look for site costs, connections, and allowances to be spelled out, so the headline figure is not undermined by exclusions you discover later.
The deposit
Victorian law caps the deposit a builder can take on a major domestic building contract. It is commonly cited as 5% for larger contracts and 10% for smaller ones [verify]. A request for a much larger upfront payment is a warning sign worth questioning.
Progress payments
Payments should be staged and tied to genuine construction milestones (for example deposit, base, frame, lock-up, fixing, and completion), with each instalment reflecting work actually done. Be cautious of front-loaded schedules that ask you to pay well ahead of progress on site.
The building schedule
The contract should include a start arrangement, a number of working days or a completion period, and how the date adjusts for genuine delays such as weather or variations. For a realistic view of overall timing, see our guide on how long it takes to build a custom home in Melbourne.
Provisional sums and PC items
A provisional sum is an allowance for work not yet fully designed; a prime cost (PC) item is an allowance for a product not yet chosen, such as tapware or tiles. Generous, realistic allowances protect you from nasty adjustments later. Finalising selections early at our studio, K Studio, with our selections consultant Nikki, is the best way to convert these allowances into firm figures.
Variations
Every change to the scope, whether requested by you or required on site, should be documented and signed as a written variation, with the price and any time impact stated before the work proceeds. Verbal variations are a frequent source of disputes.
Warranties and domestic building insurance
The contract should reference the statutory implied warranties (workmanship, materials, and compliance) and the builder's defect liability period. For most residential work above a set value, often cited as 16,000 dollars [verify], the builder must also provide domestic building insurance, which protects you if the builder dies, disappears, or becomes insolvent.
Cooling-off
Major domestic building contracts in Victoria generally include a short cooling-off period, often cited as 5 business days [verify], during which you can withdraw in writing subject to conditions. Confirm the exact period and any fee that applies.
Fixed-price vs cost-plus contracts
The pricing model shapes who carries the risk if costs move. Most homeowners building a custom home prefer the certainty of a fixed price.
Fixed-price contractCost-plus contractHow the price worksAn agreed price for the defined scopeActual costs plus an agreed builder's marginWho carries cost riskMostly the builderMostly you, the ownerPrice certaintyHigh, before you startLow until the work is doneBest suited toMost custom homes where the scope can be definedHighly uncertain or open-ended scopes
Read the deposit, payment schedule, allowances, and variation clauses before you sign.
Red flags to watch for
A deposit that looks higher than the legal cap, or pressure to pay a large amount before any documentation.
Progress payments that run ahead of the work completed on site.
Vague or missing inclusions, so the price relies on exclusions you only find later.
Unrealistically low provisional sums and PC items that all but guarantee cost increases.
No clear written variation process, or a builder happy to proceed on verbal changes.
No mention of domestic building insurance or the builder's VBA registration.
A start date with no realistic completion period or delay provisions.
KGN's transparent fixed-price approach
We build on transparent, fixed-price contracts, because certainty is part of a premium experience. As an end-to-end custom home builder, we define the scope properly during design, set realistic allowances, and finalise selections early so fewer figures are left provisional. Every variation is documented and agreed before work proceeds, and your payment schedule follows real progress on site.
This is one of the clearest differences between a design-led builder and a high-volume operator. If you are comparing your options, read our breakdown of a custom builder vs a volume builder in Melbourne. We always recommend you have your contract reviewed by your own solicitor before signing.
Frequently asked questions
What is the maximum deposit on a building contract in Victoria?
Victorian law caps the deposit a builder can take on a major domestic building contract. It is commonly cited as 5% for larger contracts and 10% for smaller ones [verify]. Treat any request for a much larger upfront payment as a red flag and check the current rule before signing.
Is there a cooling-off period on a building contract?
Major domestic building contracts in Victoria generally include a short cooling-off period, often cited as 5 business days [verify], during which you can withdraw in writing subject to conditions. Confirm the exact period and any fee that applies before you rely on it.
What are provisional sums and PC items?
A provisional sum is an allowance for work that is not yet fully designed or priced. A prime cost (PC) item is an allowance for a product you have not yet selected, such as tapware or tiles. If the real cost differs from the allowance, the contract price adjusts up or down.
Fixed-price or cost-plus, which is better for a custom home?
A fixed-price contract gives you a known price and shifts cost risk to the builder, which suits most homeowners who want certainty. Cost-plus means you pay actual costs plus a margin, with less price certainty. KGN works on transparent fixed-price contracts.
What is domestic building insurance?
Domestic building insurance, sometimes called builders warranty insurance, protects you if the builder dies, disappears, or becomes insolvent and cannot finish or fix the work. It is generally required for residential work above a set value, often cited as 16,000 dollars [verify], and the builder must arrange it.
Can the price change after I sign?
In a fixed-price contract the agreed price holds unless there is a variation, a provisional sum or PC item that differs from its allowance, or a contracted cost adjustment. Every change should be documented and signed as a written variation before the work proceeds.
Build with a contract you can trust
We will walk you through our transparent fixed-price contract line by line, so you know exactly what you are signing.
This article is general information, not legal, planning, or financial advice. Rules, costs, and timeframes vary by site and change over time. Confirm the details for your project with your council, building surveyor, or the KGN Homes team.
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