What is an interim valuation and who produces it?

An interim valuation is the assessment, made at set points through a job rather than only at the end, of what the works are worth so far: measured progress against the priced items, materials on and sometimes off site, and variations valued to date. It exists because construction work is paid for as it goes, and it says how much has been earned by this point. Who produces it depends on which side you are on: a subcontractor or contractor values their own works to build a payment application, while the party paying, or its surveyor, values to decide what to certify, and the two are reconciled through the payment machinery. The important thing is that a valuation is a measure, not an invoice: build it against the pricing document line by line, not by taking last period's figure and adding a percentage. Done properly it carries its own workings, so the number can be explained and defended; done from memory it is soft, gets cut, and has to be argued again next period. Because everything downstream, the application, the certificate, the cash the job lives on and the final account, is built on this figure, a measured and recorded valuation is worth far more than the few extra hours it takes.

Take a groundworks subcontractor on a JCT subcontract whose valuations are a single spreadsheet line each period, a percentage against each bill section, nudged up from last time. The contractor's surveyor, unable to see how any figure was reached, certifies conservatively and the applications run persistently light. The rebuilt approach is not more effort but different effort: each period the works are measured against the priced bill, a drawing is marked up to show which plots are complete, and the measure is written beside each line. The first measured valuation is certified almost in full, and the following periods start from that agreed base rather than reopening it. The number stopped being an assertion to discount and became a measure the assessor could check, which is the difference between a valuation and a guess.