A provisional sum can keep a residential tender moving when the documentation is not ready to price properly. Used carelessly, it can also hide a major scope gap, create an uncompetitive contract figure, or leave the builder carrying the commercial fallout. Knowing when to use provisional sums comes down to one question: is the work genuinely unable to be measured and priced with reasonable certainty at tender stage?
For Australian residential builders, provisional sums are not a substitute for estimating. They are a controlled allowance for work that cannot yet be defined. The measured scope should still be measured, trade-priced where possible, and set out clearly in the BOQ. The provisional sum should sit beside it, with a stated assumption, inclusions and exclusions, and a clear path for replacing it with a firm price.
What a provisional sum is - and is not
A provisional sum is an allowance for a particular item of work where the final scope, quantity, method or cost cannot be accurately determined when the contract is priced. It should cover both supply and installation where applicable, rather than becoming a vague line for an entire trade package.
For example, a DA-stage set may identify external works but provide no final landscaping plan, retaining-wall engineering or detailed levels. You may be able to measure the known paths, driveway areas and basic excavation, but not the final retaining solution. A provisional sum for the undefined retaining component may be appropriate, provided the allowance is separated from the measured external works already included.
It is not the same as a prime cost item. A prime cost item generally covers the supply cost of a selected item not yet chosen, such as sanitaryware or tiles. A provisional sum covers work or a work package where the extent itself remains uncertain. The distinction matters because the risk, margin treatment and variation process can differ under the contract.
It is also not a contingency. Contingency is an internal commercial provision for estimating risk. A provisional sum is disclosed in the tender or contract for a defined but unresolved scope item. Blending the two makes it harder to explain the estimate and harder to manage the job once it is live.
When to use provisional sums in residential work
Use a provisional sum where there is a real information gap, not merely because a trade is difficult to price. A capable estimator should first exhaust the available documents: architectural drawings, site plan, engineering, BASIX or NatHERS information, hydraulic design, consultant reports, authority requirements and finishes schedules. The goal is always to convert uncertain scope into measured scope before issuing the tender.
Provisional allowances are often justified in these situations:
- Unresolved site conditions, particularly where a geotechnical report, detailed survey, service location or final excavation methodology is unavailable.
- External works with incomplete levels, landscape documentation, retaining-wall design, stormwater details or driveway specifications.
- Authority-driven items where final requirements are still pending, such as service upgrades, road-opening requirements or specific site controls.
- Renovation and addition work where concealed conditions cannot be confirmed without demolition or investigation.
- Consultant-designed elements that are identified in principle but not documented sufficiently to obtain a comparable subcontractor price.
The key test is whether the item can be isolated. “Provisional sum for site works” is usually too broad to be useful. “Provisional sum for rock excavation below design excavation level, including removal from site” is far more controllable. It tells the client, superintendent and project team what the allowance addresses, while preserving the measured excavation already included in the tender.
Do not use allowances to cover incomplete estimating
A provisional sum should not be the first response to programme pressure. If the plans show enough information to take off a quantity and apply a credible rate, measure it. If a subcontractor can price it from the available documents, seek the price. If comparable recent jobs provide a defensible rate, use that rate and document the basis.
The most common tender problem is a broad allowance used to get a number out the door. It may make the headline contract sum look lower, but it shifts the difficult conversation downstream. Once the job starts, the client sees variations, the builder has to justify costs, and the programme can be affected while design decisions catch up.
This is particularly relevant on duplexes and triplexes, where civil works, stormwater, service connections and fire-related requirements can carry material uncertainty. A single generic provisional sum can conceal multiple unrelated risks. Break them into discrete items so each can be reviewed, adjusted and converted to a firm price independently.
How to set the allowance properly
A provisional sum still needs estimating discipline. Start with the best available scope definition, then obtain market input where it is practical. A civil subcontractor may be able to provide a budget range for retaining or deep excavation even before final design. Local pricing matters here. Metro rate cards may not reflect cartage, crew availability, disposal costs or plant mobilisation in regional NSW, QLD or VIC.
The allowance should be based on a stated quantity or scenario where possible. Rather than carrying a round figure for excavation, document the assumed volume, spoil classification, haulage distance and disposal basis. For a provisional retaining wall, note the assumed wall type, height range, access conditions and whether engineering, drainage and finishes are included.
Include the builder’s normal margin, preliminaries and supervision treatment in accordance with the contract and tender structure. This needs to be explicit. A provisional sum that looks adequate at trade cost can still erode margin if site supervision, coordination, programme impacts and builder’s margin are not addressed when the work is instructed.
Your estimate should show the allowance separately from measured trade scope. In an editable BOQ, that means a dedicated provisional sums section with a reference back to the relevant trade package. It prevents double counting and lets the estimator test the tender total if the allowance is replaced by a subcontractor quote later.
Write assumptions that survive handover
The allowance description is as important as the dollar figure. A good description lets the estimator, contracts administrator, site supervisor and client understand the original basis without hunting through emails months later.
For each provisional sum, record what is included, what is excluded, the pricing basis, the documentation missing at tender stage, and the event that will trigger final pricing. If the allowance depends on a future engineering design, say so. If it excludes rock, contaminated material, latent conditions or authority fees, say so plainly.
Avoid wording such as “allow for all required works” or “as necessary”. Those phrases offer no commercial control. They can also create an argument that the builder should have allowed for a broader scope than intended.
A useful practical approach is to align each allowance with the construction programme. Ask when the information must be finalised to avoid holding up procurement or site works. If stormwater design is outstanding but excavation starts in six weeks, it is not enough to place an allowance in the estimate. Someone needs ownership of obtaining the design, issuing it for trade pricing and approving the final cost before it becomes a programme problem.
Manage provisional sums after the tender
The estimate is only the starting point. Once the project moves forward, provisional sums should be actively reduced. Issue targeted subcontractor pricing packs, obtain missing consultant details and replace allowances with firm scope packages as early as possible.
Track each item in a live register showing the original allowance, current forecast, approved value, remaining exposure and required decision date. This is particularly useful where several allowances affect the same trade or sequence of works. It gives the pre-construction team and site team one version of the commercial position.
Where a subcontractor quote exceeds the allowance, review why before simply passing through the difference. Has the scope grown? Was the original documentation unclear? Has access changed? Is the market rate different from the rate used in the estimate? That review improves the current job and sharpens the rate cards and estimating assumptions used on the next one.
A cleaner way to price uncertain scope
At DA stage, some uncertainty is unavoidable. The answer is not to pretend every package is fully documented, nor to load the tender with unexplained allowances. Measure what can be measured, identify what cannot, and make each provisional sum specific enough to manage commercially.
A structured estimating pack makes this easier: measured quantities in the BOQ, clear provisional allowances, subcontractor-ready scope packages and an indicative construction programme that shows when decisions are needed. EstiFlow can turn DA-stage plans into that builder-ready structure typically within 1 business day, giving your team an editable starting point rather than a black-box total.
Before the tender goes out, compare every provisional sum against a past priced job with similar site conditions and scope. If you cannot explain the basis in a short handover conversation, the allowance is not ready to carry the risk.