Why My Pool Cost More Than the Contract

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Most pool overruns come from five places: rock in the excavation, site access, provisional sum reconciliation, client changes and prime cost adjustments. Excavation and access alone run $8,000 to $35,000. In Queensland a variation must be agreed in writing before the work starts, with a copy within 5 business days.

The short answer

Rock is the biggest single cause. It is usually a provisional sum, which means an estimate, not a price.
Queensland: a variation must be in writing and agreed in writing before the work starts, with a copy within 5 business days.
A provisional sum is only allowed where the builder cannot state a definite amount after making all reasonable enquiries.
Prime cost items are fixtures and fittings; provisional sums are services like rock or termite removal. They reconcile differently.
You are entitled to ask for an itemised breakdown of any variation. Ask before you pay it, not after.

The five ways a pool ends up costing more than the contract
Cause	What it looks like on the invoice	Was it foreseeable?
Rock in the excavation	A rock rate per hour or per cubic metre, against a provisional sum allowance	Yes — a soil test or borehole before signing tells you the risk
Site access	Extra machinery, hand digging, crane hire, fence removal and reinstatement	Yes — access width is measurable before anyone quotes
Provisional sum reconciliation	The allowance replaced by the actual cost, up or down	Partly — you can ask how the allowance was calculated
Client-requested changes	A variation: bigger, deeper, different tile, added spa or heating	Entirely within your control
Prime cost item adjustment	The chosen fitting costs more than the allowance carried in the contract	Yes — ask what the allowance buys before you sign

The rules a variation has to follow

This is the part most owners never read, and it is the part that decides arguments. In Queensland, before the contractor starts variation work they must present the variation to the owner in writing and the owner must agree to it in writing. A copy must be given before the domestic building part of the variation work starts, or within 5 business days of both parties agreeing, whichever comes first. The only exception is urgent work where producing a written copy first is not reasonably practicable.

The document itself has to be readable and specific: it must describe the variation, state the date of the request, state any delay it causes, and state the price change or the way the price will be calculated.

Victoria runs the same principle through the Domestic Building Contracts Act 1995, requiring a written variation notice describing the change. So if your invoice contains work you agreed to in a phone call, the process was not followed — and that is a fact worth stating, calmly, in writing.

Rock, and why it is almost always a provisional sum

The QBCC defines a provisional sum as an estimate of the cost of providing particular contracted services, used only where the contractor cannot state a definite amount after making all reasonable enquiries — and it gives rock removal as the example. That is an honest instrument being used honestly: nobody knows what is three metres under your lawn.

The obligation is that the allowance is calculated with reasonable care and skill. An allowance set deliberately low to make a quote look competitive is the failure mode, and it is why two quotes for the same pool can differ by $15,000 on paper and be identical in reality.

Before you sign, the useful questions are: what is the rock allowance, how was it calculated, what is the rate once the allowance is exhausted, and who decides that rock has been hit. What a provisional sum is covers the mechanics, and whether you need a soil test covers how to price the risk down before it becomes a variation.

What to do when the invoice arrives

Work through it in this order, and in writing.

Separate variations from reconciliations. A variation is a change to the scope. A provisional sum reconciliation is the same scope at its actual cost. They are governed differently and it is common for an invoice to blur them.
Ask for the itemised breakdown of each variation — labour, materials and quantities, subcontractor costs, plant hire. You are entitled to ask, and a legitimate variation survives the question easily.
Check each variation against the paperwork. Was it in writing? Did you agree in writing? Was it before the work started?
Check the payment stage. A progress claim has to match the stage actually reached. See deposit limits and progress payments.
Pay the undisputed part. Withholding everything weakens a good argument about the disputed part.

If you cannot agree

Put the disagreement in writing with the contract clause and the invoice line side by side, and ask for a response by a date. If that fails, the dispute path is the same as for defects: the QBCC in Queensland, NSW Fair Trading and then the tribunal in New South Wales, and Domestic Building Dispute Resolution Victoria before VCAT.

Unwritten variations are not automatically unenforceable — a builder may still have avenues to recover the value of work you asked for and received — but the process failure is relevant, and the regulators say plainly that failing to record and approve variations before they happen is one of the most common causes of serious building disputes.

If the relationship has broken down entirely, the defects escalation path has the statutory deadlines you need to protect.

Common questions

Does a variation have to be in writing in Queensland?

Yes. The QBCC states that before commencing variation work the contractor must present the variation to the home owner in writing and the home owner must agree in writing, with a copy provided before the work starts or within 5 business days of agreement, whichever is first — see QBCC on contract changes and variations. Urgent work is the only exception.

What is the difference between a provisional sum and a prime cost item?

The QBCC describes provisional sums as contracted services such as rock or termite removal, and prime cost items as fixtures and fittings such as tiling and appliances. Both must be calculated with reasonable care and skill. A provisional sum reconciles against what the service actually cost; a prime cost item against what you chose.

Can the builder charge me for rock without telling me first?

If rock is carried as a provisional sum in your contract, the allowance being exceeded is a reconciliation rather than a new variation — which is exactly why the allowance, the rate and the trigger should be settled in the contract. Ask for the measurement and the evidence supporting the claim.

How much rock allowance is normal?

There is no standard figure, and any single number would be misleading — it depends on the geology of the block. What is comparable between quotes is the rate and the method, not the allowance. Two builders quoting the same rate with different allowances are quoting the same job.

Sources

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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