Prime cost item vs provisional sum: what is the difference?

They appear on adjacent lines of the same schedule, they are both described as allowances, they both come with an acronym, and at the meeting where they were explained you almost certainly nodded. Everyone does. The builder said something about tapware and something about excavation, the conversation moved on, and you were left holding two terms that sound like the same idea expressed twice. It is not a failure of attention. Prime cost items and provisional sums are genuinely similar in appearance and entirely different in function, and almost nobody explains the difference in a way that survives the drive home.

Here is why it matters more than the paperwork suggests. These two mechanisms are the reason a fixed-price contract is not a fixed price. Every one of them is a number that will change after you have signed, and they change in only one direction more often than not — quietly, one selection at a time, in amounts too small to argue about individually. Most owners discover the distinction at the first adjustment, which is precisely too late to do anything about it. The good news is that the difference is genuinely simple, and once you can see it you can read your own contract and know exactly where it is exposed. A prime cost item is a thing you have not chosen yet. A provisional sum is work nobody can measure yet. That single sentence resolves most of the confusion, and everything below follows from it.

The difference, at a glance

That last row is the one worth holding onto. A provisional sum is largely out of your hands. A prime cost item is almost entirely within them.

A prime cost item is a product

A prime cost item, usually written as a PC item, is an allowance for the supply of something you have not yet chosen — tapware, tiles, a cooktop, door hardware, light fittings.

The critical feature is that the installation labour is already priced elsewhere in the contract. The builder has allowed for a plumber to fit a mixer. What has not been settled is which mixer. When you select, only the product cost adjusts.

A provisional sum is work

A provisional sum covers both the supply and the labour for work whose extent is genuinely unknown at signing — excavation, rock removal, underpinning, service connections, asbestos removal, landscaping.

Nobody knows how much is required until the work begins. The allowance is reconciled once it does, usually at the progress claim covering that stage, and the builder substantiates the actual cost.

The test that resolves any line in your schedule

Look at the description and ask one question:

Is this a product I will choose, or work someone has to perform?

Tapware, tiles, appliances, hardware — products. You choose them, and the choice is yours to control.

Excavation, drainage, rock, connections, removal — work. The site decides, not you.

Where a line is genuinely ambiguous — landscaping is a common one, since it involves both supply and labour — ask the builder which mechanism the contract treats it as, because the answer changes how it adjusts and what evidence you are entitled to.

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Why the distinction matters commercially

Three consequences follow from it, and each one is worth money.

You control one and not the other. Every prime cost item can be converted into a fixed figure by making the selection before signing. A provisional sum usually cannot, because the uncertainty is in the ground rather than in your indecision. Knowing which of your allowances are actually convertible tells you where to spend your effort before the contract is signed.

They fail differently. Provisional sums tend to move in large, visible amounts — a rock clause, an unexpected connection. Prime cost items move in small ones, thirty or forty times over, with margin applied to each. One produces an argument. The other produces a slow drift nobody notices until the final account.

The evidence you are entitled to differs. For a provisional sum you should expect substantiation of the actual cost. For a prime cost item the evidence is the supplier's price for what you selected. Knowing which you are looking at tells you what to ask for.

Both are regulated, and both must be documented

Australian residential building contracts treat these allowances seriously. In broad terms, each prime cost item and each provisional sum should appear in its own schedule with a detailed description, the amount allowed, and the margin applying to adjustments together with how it is calculated.

The state-by-state requirements — including the warranty that allowances be calculated with reasonable care, the prohibition on setting them unreasonably low, and the substantiation a builder must provide — are set out in detail in the provisional sums article, and apply to prime cost items in the same way.

An allowance described only as "tapware allowance" or "site works" with a figure beside it is not a compliant schedule.

What to do before you sign

1. Sort every allowance in your schedule into the two columns using the test above.
2. Total each column and express both as a percentage of the contract price. That figure tells you how fixed your fixed price actually is.
3. Convert the prime cost items by making your selections before signing. Every one you finalise is a number that can no longer move.
4. Attack the provisional sums with information. A soil test and contour survey of your own converts the largest and most common allowance — site costs — into a priced item.
5. Confirm the margin rate in writing, and whether it applies to credits as well as increases.

Common questions

Which one is riskier?

Provisional sums carry the larger single surprises, because the uncertainty is in the ground. Prime cost items carry the larger cumulative drift, because there are more of them and each adjustment feels trivial. Neither is inherently worse — they fail in different shapes.

Can something be both?

Not on the same line. But a single scope — landscaping, for instance — may be split, with plants and materials as prime cost items and the labour as a provisional sum. Ask how yours is structured.

Do both attract the builder's margin?

Usually, applied to the difference between the allowance and the actual cost. The rate must be stated in the contract, and it is applied before GST.

Do adjustments to either count toward contract price escalation limits?

In some jurisdictions, valid prime cost and provisional sum adjustments are excluded from the thresholds that give owners a right to end a contract. The Victorian position is covered in the provisional sums article, and it is a strong reason to count your allowances carefully before signing.

How many of each is too many?

Judge by value rather than count. Once allowances represent a significant share of the contract price, you are signing an estimate with a fixed-price heading.

Where to go next

These are two of the four mechanisms that move the price of a fixed-price contract. The others are variations and price rise clauses.

Read next: what a prime cost item is for the detail on selections, accumulation and how to keep control of them, or what a provisional sum is for the adjustment process, state requirements and how to reduce them before signing.

One is a thing you will choose. The other is work nobody can measure yet. Knowing which is which turns a schedule you nodded at into a document you can actually read.