What is a prime cost sum in a construction quote?

A prime cost sum, often shortened to PC sum, is an allowance whose meaning must be checked in the actual quote or contract. Under NRM 2, it is an allowance within a unit rate for supplying materials or goods whose precise quality is not yet settled. That supply allowance excludes installation and the other costs identified by those measurement rules. Do not assume every builder uses the abbreviation in the same way.

Ask whether the allowance is a rate or a total, which quantity it applies to, what product or quality it assumes and what evidence will replace it. Check how the documents deal with delivery, waste, fixing, ancillary materials, preliminaries, overheads and profit, and VAT. Record where each cost is included so it is neither missed nor added twice.

A provisional sum addresses work that is not sufficiently defined at that point. It is a different allowance to investigate, rather than another name for a PC sum. For either one, establish the agreed adjustment basis and keep the original allowance visible beside the later selection or quotation.

Tender & Quote Review can check the actual allowances and exclusions across your quotations. The existing provisional-sum answer explains the separate uncertainty about the work itself.

Worked illustration

Illustrative supply-only comparison: a quote allows 20 m² of tiles at £30/m², giving £600. The selected tiles are quoted at £38/m², giving £760 on the same quantity. The difference is 20 × (£38 − £30) = £160. These invented figures exclude waste, delivery, fixing, markup and VAT for the comparison. Check how the actual quote treats those items and adjusts the allowance before treating £160 as the change to the amount payable.

Source: RICS NRM 2, second edition UK, October 2021, glossary, printed page 10 (PDF page 16).