Provisional Sums
By George Giannakakis · M.Arch · RLA300580 · HIA Industry Judge
Last reviewed: · How we research
Provisional Sums explained in detail
An estimate in a building contract for the cost of completing a specific scope of work (including materials and labour) where the builder cannot provide a definite amount after reasonable inquiries. Common provisional sums include excavation, landscaping, site preparation, electrical works, and retaining walls. If actual costs differ from the allowance, the contract price is adjusted accordingly. Provisional sums are one of the most common sources of budget blowouts in Australian building. It's not unusual for a PS allowance for site costs to come in significantly higher once actual conditions are discovered. Under standard building contracts, builders are expected to base provisional sums on reasonable inquiry. It is worth asking your builder to justify every provisional sum in writing before signing.
Related Terms
Frequently Asked Questions
Common questions about provisional sums
Prime Cost (PC) covers specific items like taps, tiles or appliances - just the product cost, not installation. Provisional Sum (PS) covers entire work packages including labour and materials, like excavation, retaining walls or landscaping. Both are estimates adjusted to actual costs. The key difference: PC items you can choose or change, while PS items are often site-dependent and out of your control.
Contract and legal information
Building contracts, dispute resolution, and consumer law are complex and vary by state and contract type. The information here is general in nature and may not apply to your situation. For advice about your specific contract, rights, or dispute, speak with a building lawyer, your state’s consumer protection body, or a licensed building consultant.
Cost figures are indicative onlyUpdated February 2026
All prices and cost ranges mentioned are approximate, based on Adelaide market conditions at time of writing, and may not reflect current pricing. Actual costs depend on your specific site, design, builder, materials, and market conditions. Project-specific quotes from qualified professionals are needed for accurate pricing.
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National
The primary national set of technical building standards that every Australian build must comply with. Volume 2 covers Class 1 & 10 buildings (most homes).
Specific material, product and method standards (e.g. AS 3700 masonry, AS 1684 timber framing) referenced by the NCC.
National peak body for residential builders. Publishes the most widely used home-building contracts and consumer guidance.
National peak body for general builders. Publishes commercial and residential contracts and industry guidance.
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