Prime Cost (PC) Sum
An allowance for materials or goods whose supplier or specification is not yet fixed — the contractor prices the installation, and the supply cost is adjusted against the allowance when the actual item is selected.
The distinction from a provisional sum is worth keeping straight: a PC sum covers the SUPPLY of an identified item whose cost is not yet known, while a provisional sum covers WORK whose scope is not yet defined. The contractor’s profit and attendance on a PC item are priced separately in the bill.
PC sums are where specification creep is quietly funded on fit-out projects. The allowance was set at a sensible rate; the interior designer then selects something considerably more expensive; and the adjustment is a variation everybody saw coming and nobody budgeted for.
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