#fixedpricebuild

"Fixed price" is one of the most reassuring phrases in home building, and also one of the most misused. For a luxury custom home, where the finishes and scope are more complex than a project home, the term can mean genuinely different things depending on how the contract is written. Understanding what should sit inside a truly fixed price, and where the gaps usually hide, matters more the larger and more detailed the build.

What "Fixed Price" Is Supposed to Mean

A fixed-price contract is meant to give you cost certainty: the agreed price covers the agreed scope, and you're not exposed to material or labour cost increases during the build. For that promise to hold, the scope has to be defined in enough detail that there's no ambiguity about what's included. A vague scope with a fixed number attached to it isn't cost certainty, it's a number that will move once the ambiguity is resolved during construction.

Where Provisional Sums Hide the Real Cost

Provisional sums are the most common place a "fixed price" quietly stops being fixed. A provisional sum is an estimated allowance for an item that hasn't been fully specified yet, often for things like external landscaping, driveways, or certain fixtures. They're not inherently a problem, every build has some genuine unknowns, particularly around site conditions. The issue is when provisional sums are used for items that could and should have been specified upfront, such as tapware, tiling or joinery finishes, in order to make the headline price look lower than the real cost of the home you're describing. Ask directly how many provisional sums are in your contract and what each one covers.

Exclusions Worth Reading Line by Line

Exclusions are the flip side of provisional sums; items left out of the price entirely rather than estimated within it. Common exclusions on a luxury build can include things like final landscaping, fencing, pool infrastructure, driveway paving, or council and authority connection fees. None of these are wrong to exclude, but they need to be listed explicitly and priced separately so you know your actual total cost before you sign, not partway through construction when the invoices start arriving.

Specification Detail Is What Makes a Fixed Price Meaningful

The strength of a fixed-price contract comes directly from the strength of the specification behind it. A specification that names the actual stone, tile range, appliance brand and model, and joinery finish removes the ambiguity that leads to disputed variations later. In a luxury home build, where finishes are a meaningful part of the cost, a vague specification is where "fixed price" quietly becomes negotiable. Before signing, it's worth asking to see the full specification document, not a summary, and checking it names products rather than describing them generically.

How Variations Clauses Should Work

Even a well-specified luxury custom home can have legitimate variations, usually where a client changes their mind on a finish or where a site condition wasn't visible until excavation. What matters is how the contract handles them. A clear variations clause sets out how a variation is priced, documented and approved before the work happens, in writing, with a cost attached, so there are no surprises at the next progress claim. If a builder is vague about how variations are handled when you ask, treat that as a signal worth taking seriously.

Questions to Ask Before You Sign a Fixed-Price Contract

Ask how many provisional sums are in the contract and get a written estimate for each. Ask for a full list of exclusions with their estimated cost, even if it's not part of the contract price. Ask to see the detailed specification, not a summary sheet. Ask how variations are priced and approved, and ask for that process in writing. These are reasonable, standard questions, and a builder who has nothing to hide will answer them clearly and promptly.

Frequently Asked Questions

Are provisional sums always a bad sign? No. Genuine unknowns, like unforeseen site conditions below ground, are reasonably handled as provisional. The concern is when items that could be specified upfront are left as provisional to lower the headline price.

Can a fixed-price contract still change after signing? Only through a properly documented variation, agreed and priced in writing before the work proceeds. If a price changes without that process, that's worth raising immediately.