A provisional sum in construction contracts is a monetary allowance written into the contract price as a placeholder for work the parties know will happen but cannot yet fully define or price. It sits inside the total contract sum from day one, lets the project move forward while design details, material selections, or site conditions are still being resolved, and gets replaced later by the actual value of the work once a formal instruction is issued. If the real cost comes in lower than the allowance, the contract price drops. If it comes in higher, the price goes up.
What the Allowance Is For
A provisional sum targets work that is foreseeable but lacks the detail needed for a firm price at tender. A commercial fit-out might include one for fire suppression upgrades the fire engineer hasn’t finalized. A refurbishment might include one for remedial work whose extent won’t be visible until demolition begins. Specialized finishes not yet selected, utility connections the service provider hasn’t confirmed, and similar items all sit comfortably in this category.
What a provisional sum is not: a slush fund. It’s earmarked for a specific category of work described in the contract documents. The contractor cannot redirect those funds to cover unrelated expenses, and the owner cannot treat the allowance as a general pot of money for anything that comes up during the job. Each sum should have its own line in the bill of quantities or contract sum analysis, with a description that makes clear what the money is set aside for.
Provisional Sum or Contingency?
These two get confused constantly, and the difference changes how the money is controlled.
A provisional sum covers a known item of work where the details are still vague. It will almost certainly be spent, because the work itself is expected. A contingency fund covers events that may never happen at all, like discovering contaminated soil or weather damage beyond what the schedule anticipated. A contingency may never be touched.
Control also differs. An owner’s contingency sits outside the contractor’s scope entirely, available for the owner to authorize at their discretion. A contractor’s contingency covers risk within the contractor’s own work. Provisional sums, by contrast, are part of the contract sum from the start and get converted to actual expenditure through a formal instruction or change order.
Defined vs. Undefined: Where the Real Money Sits
This single distinction drives the biggest financial consequence in provisional sum work: who absorbs the cost of scheduling disruption and site overhead when the work is finally ordered.
Defined Provisional Sums
A provisional sum qualifies as “defined” when the contractor receives enough information at tender to plan for the work in their program. Under the Royal Institution of Chartered Surveyors’ measurement rules (NRM2), four pieces of information must be provided: the nature and construction of the work, a statement of how and where it fits into the building, quantities indicating the scope and extent, and any specific limitations that apply.1RICS. NRM 2: Detailed Measurement for Building Works Because the contractor can reasonably incorporate the work into their construction schedule, they’re expected to have priced their preliminaries and overhead accordingly. When the instruction to proceed arrives, they’re not entitled to claim extra time or management costs.
Undefined Provisional Sums
If any of those four information requirements is missing, the work must be treated as undefined, regardless of how it’s labeled in the bill of quantities.1RICS. NRM 2: Detailed Measurement for Building Works The contractor is deemed not to have made any allowance for the work in their program, planning, or preliminaries pricing. The financial consequence falls on the owner: the contractor can claim additional time, extended preliminary costs, and compensation for disruption to existing planned work. A sum labeled “defined” but missing one of the required pieces of information gets reclassified as undefined. The label does not control the outcome; the quality of the information does.
The practical gap between the two can mean tens of thousands in additional preliminaries for the same scope of physical work. That is why owners and their advisors push to turn as many sums as possible into “defined” ones before tender closes.
Which Rules Apply Depends on Your Contract
The defined/undefined framework is not universal. Different standard form contracts take meaningfully different approaches, and the rules that apply to your project matter more than the general concept.
JCT (Joint Contracts Tribunal)
JCT contracts, widely used in the UK, adopt the NRM2 definitions above. Under the JCT Standard Building Contract with Quantities (SBC/Q 2016), the architect or contract administrator issues an instruction under clause 3.16 to expend the provisional sum, and the financial adjustment follows under clause 4.3.5. The contract sum is adjusted by deducting all provisional sums and replacing them with the value of the work actually instructed. Whether the contractor gets additional time and preliminaries money depends entirely on whether the sum was properly defined at tender.
FIDIC (International Federation of Consulting Engineers)
FIDIC contracts, common on international infrastructure and civil engineering projects, take a simpler approach. Clause 13.5 of the FIDIC Red Book states that each provisional sum may only be used in accordance with the Engineer’s instructions, and the contract price adjusts accordingly. The Engineer can instruct the contractor to execute the work (valued as a variation) or purchase materials and services from a nominated subcontractor, with the contractor entitled to add overhead and profit at a percentage stated in the contract schedules.2Central Procurement Portal. General Conditions – FIDIC Red Book FIDIC does not distinguish between defined and undefined provisional sums. The contractor must produce quotations, invoices, vouchers, and receipts to substantiate costs when required.
AIA (American Institute of Architects)
US practice generally uses the term “allowance” rather than “provisional sum,” though the concept is functionally similar. If you’re working in the US and someone mentions provisional sums, the closest equivalent in your contract is almost certainly an allowance under Section 3.8 of the AIA A201-2017 General Conditions. Allowances cover the cost of materials and equipment delivered to the site, including required taxes and minus trade discounts. They do not cover labor, installation, handling, overhead, and profit; the contractor must price those separately in the contract sum.3University of Wisconsin. AIA A201-2017 General Conditions of the Contract for Construction When actual costs differ from the allowance, the contract sum is adjusted by change order reflecting both the material cost difference and any resulting changes in the contractor’s labor and installation costs.4AIA Contract Documents. Construction Allowances Explained: What Contractors Need To Know
The owner selects the materials and equipment covered by allowances, and Section 3.8.3 requires the owner to do so with “reasonable promptness.” Delay in making selections can trigger claims for extended overhead, much as undefined provisional sums do under JCT.
NEC (New Engineering Contract)
NEC contracts deliberately avoid provisional sums altogether. The NEC approach requires the parties to state clear assumptions about defined cost and time for any potentially required work, and bidders build those assumptions into their prices and programs. If the assumptions change, the change is managed as a compensation event.5NEC Contract. Words and Phrases to Avoid When Talking About NEC Contracts Parties working under NEC should not attempt to insert provisional sum clauses borrowed from other contract forms.
How the Allowance Converts to Real Money
The adjustment process has a clear trigger: the contract administrator, engineer, or architect issues a formal instruction authorizing the contractor to proceed with the work. Until that instruction is issued, the contractor has no right to spend the provisional sum. Under FIDIC, the instruction comes from the Engineer. Under JCT, from the architect or contract administrator. Under AIA, the owner directs the selection and a change order formalizes the adjustment.
Once instructed, the contractor either provides a quotation based on the now-defined scope, or the work is valued after completion using the contract’s variation pricing rules. The original provisional sum is deducted from the contract sum and replaced with the actual value of the instructed work. Under FIDIC, the contractor must produce quotations, invoices, vouchers, and receipts to support the claimed amounts.2Central Procurement Portal. General Conditions – FIDIC Red Book Under AIA contracts, the change order captures two separate components: the difference between actual material and equipment costs and the original allowance amount, plus any resulting change in the contractor’s costs for labor, handling, and installation.3University of Wisconsin. AIA A201-2017 General Conditions of the Contract for Construction The two-part structure prevents disputes about whether an overhead and profit adjustment is legitimate when material costs change significantly.
Where Disputes Reliably Start
Who Bears the Estimating Risk
The contractor bears no risk for whether the provisional sum accurately reflects the actual cost of the work. RICS guidance is explicit: the adequacy of the estimate is the employer’s problem. If the sum for mechanical ventilation was set at $80,000 and the work ultimately costs $130,000, the contractor is entitled to be paid the full $130,000, assuming the instruction and valuation followed proper procedures. The owner absorbs the difference. An artificially low provisional sum does not save money; it just delays the shock.
Omission of the Work
Owners sometimes decide not to proceed with provisional sum work at all, or attempt to remove it from the contract and give it to a different contractor. This creates breach of contract exposure. Under many JCT contracts, provisional sum work forms part of the contracted scope regardless of how vaguely it’s described. Removing the work without valid justification can entitle the original contractor to claim lost profit. English courts have upheld this principle, finding that arbitrary withdrawal of provisional sum work amounts to a breach for which the contractor can recover damages.
Defined/Undefined Fights
The most financially consequential disputes center on whether a provisional sum was properly defined. A contractor facing an instruction for undefined work can claim extensions of time and additional preliminaries costs — crane hire, site management, welfare facilities — for the period needed to complete the work. These indirect costs often exceed the direct cost of the work itself. Owners who provide incomplete information at tender, whether to keep the headline price down or through oversight, end up paying significantly more than they would have if the sum had been properly defined from the start.
What Each Side Should Actually Do
For owners and their advisors, the goal is to minimize undefined provisional sums. Every sum that can be pushed into the “defined” category through better design information at tender shifts the scheduling and overhead risk to the contractor. Investing in early-stage design work pays for itself several times over when it prevents preliminaries claims later. If undefined sums are unavoidable, budget separately for the additional time and cost claims that will follow when those instructions are issued.
For contractors, the critical step is reviewing provisional sums during tender and flagging any labeled “defined” but lacking the four required pieces of information under NRM2 or its equivalent. Accepting a “defined” label without scrutiny means accepting the programming and overhead risk that comes with it. If the information is incomplete, raise it before signing. At minimum, record your position in writing so the reclassification to “undefined” is clear if the point is later disputed.
Both sides benefit from early instructions. The longer an owner waits to firm up provisional sum scope, the more disruptive the work becomes to the construction program. Late instructions on significant provisional sums are among the most reliable generators of delay claims and cost overruns in construction disputes.