What is a provisional sum in a pool quote?
It is the line that makes two pool quotes look thousands apart when they are not — and the one item in a building contract, alongside the excavation and the barrier, that is allowed to be an estimate rather than a fixed price.
A provisional sum is an estimate of the cost of a contracted service the builder cannot price definitely — rock in a pool excavation is the standard example. The QBCC allows it only where a definite amount cannot be stated after all reasonable enquiries. Excavation costs $8,000 to $35,000, against $80 to $600 a metre for the barrier.
The short answer
- A provisional sum is an estimate for a service; a prime cost item is an allowance for a fitting such as coping or paving. They reconcile differently.
- It is only legitimate where the builder cannot state a definite amount after making all reasonable enquiries.
- It must be calculated with reasonable care and skill — a deliberately low allowance is the failure mode.
- Rock is the pool example. It is why one quote can look $15,000 cheaper and finish at the same price.
- Compare the rate and the method, not the allowance. Two builders with the same rate are quoting the same job.
| Provisional sum | Prime cost item | Variation | |
|---|---|---|---|
| What it covers | A contracted service — rock or termite removal | A fixture or fitting — tiling, appliances | A change to the scope of work |
| Why it exists | The amount cannot be stated definitely after all reasonable enquiries | The item has not been chosen yet | You or the builder changed something |
| How it settles | Reconciled against the actual cost of the service | Reconciled against the item you choose | Priced and agreed separately |
| Must it be agreed in writing first? | It is in the contract from the start | It is in the contract from the start | Yes — in writing, before the work starts |
| What to ask before signing | How was the allowance calculated, and what is the rate beyond it | What does the allowance actually buy | What is your process for pricing one |
The definition, and why it is narrower than builders' habits suggest
The QBCC defines a provisional sum for a domestic building contract as an amount that is an estimate of the cost of providing particular contracted services — and it applies only to services for which the builder, after making all reasonable enquiries, cannot state a definite amount when the contract is entered into.
Read that condition again, because it is doing real work. A provisional sum is not a general-purpose placeholder for anything a builder would rather not commit to. It is for genuinely unknowable items, and the obligation is that it is calculated with reasonable care and skill.
Prime cost items are the sibling concept and are different: those are fixtures and fittings such as tiling and appliances, where the allowance stands in for an item you have not chosen yet.
Why rock is the pool industry's provisional sum
Nobody knows what is three metres under your lawn until the machine gets there, which makes rock the textbook case — the QBCC uses rock removal as its own example. Excavation and site access run $8,000 to $35,000 nationally, and rock is the reason that range is as wide as it is.
Here is the practical consequence. Two builders quote the same pool. One carries a $3,000 rock allowance, the other $18,000. On paper the first is $15,000 cheaper. If the ground turns out to hold rock, both reconcile to what removing it actually cost and the difference evaporates — except that the buyer who chose on the headline number is now managing a large unbudgeted invoice.
The allowance is not the price. The rate is the price. Ask what the rate is per hour or per cubic metre once the allowance is exhausted, who determines that rock has been struck, and how it is measured. A soil test is what turns that allowance from a guess into an estimate.
What a provisional sum is not: a variation
These get conflated on invoices constantly, and they are governed differently. A provisional sum is already in your contract and reconciles to actual cost. A variation is a change to the scope, and in Queensland it must be presented in writing and agreed in writing before the variation work starts, with a copy provided within 5 business days of agreement or before the work begins, whichever is first.
So when a bill arrives, separate the two before you argue about either. A provisional sum reconciliation is answered with measurement and evidence; an unwritten variation is answered with the process the regulator requires. Why a pool costs more than the contract works through both.
The four questions to ask before you sign
- Which lines in this quote are provisional sums? If the answer is vague, that is the answer.
- How was each allowance calculated? A soil report, a neighbouring job, a site inspection — all reasonable. "Standard allowance" is not.
- What is the rate beyond the allowance, and how is it measured? This is the number that makes quotes comparable.
- Who decides the allowance has been exceeded, and what evidence do I get? Agree this before a machine is on site, not after.
Ask every builder the same four and the quotes become comparable for the first time. The twelve questions to ask before you sign covers the rest of the contract, and you can get quotes to run them against.
Common questions
Is a provisional sum allowed to go up?
What is the difference between a provisional sum and a prime cost item?
Can I ask for a fixed price instead?
Do provisional sums have to be itemised on an invoice?
Sources
- QBCC — Contracts and agreement types
- QBCC — Contract changes and variations
- QBCC — Deposits and progress payments
General information only, current at 2026-09-10. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.
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