A variation is not paid until it is valued and certified
On a JBCC job the instruction is the start, not the finish. The change is worth nothing until the quantity surveyor has priced it and the principal agent has carried it onto a payment certificate.
QScope Team · 9 February 2026 · 6 min read
Every variation on a JBCC contract follows the same path. Someone instructs a change, the work gets done, the quantity surveyor values it, and the principal agent certifies it. Skip the valuation and the change sits on site as cost the contractor has carried but cannot yet turn into cash.
Start with the authority
Before you value anything, check it was instructed. On JBCC a variation flows from an instruction issued under the contract, and the principal agent is the person with authority to issue it. A change asked for by someone on site with no authority is not a variation, it is a risk the contractor took on its own account.
- Instruction first. Tie every variation to the document that authorised it, with a date and a reference.
- Then measure. Value the work actually done, not the work first imagined.
- Then certify. The agreed figure only becomes money once it is on a certificate.
How the value is built
The order of preference is the ordinary one. Where the contract rates apply, use them. Where the work is similar but the conditions differ, use the rates as a basis and adjust. Where nothing fits, build a fair rate from first principles, or fall back to recorded time and materials where the character of the work makes measurement impossible.
The judgement is in deciding which rung of that ladder the change sits on. A like for like increase in quantity is a rated item. A change that alters the method or sequence is not, and forcing it onto a contract rate undervalues it.
Records win the argument
The variation you can prove is the variation you get paid for. Keep the instruction, the marked up drawing, the measure and, where the work went onto time and materials, the daily records signed as they happened. A claim assembled months later from memory is worth a fraction of the same claim backed by contemporaneous records.
Carry it into the certificate
Agreed variations do not live in a separate world. They join the gross value on the next interim payment certificate, they attract retention like any other work, and they carry VAT at 15 per cent on the net. Value them, agree them, and get them certified in the cycle they were done, because a variation that slips uncertified for three months is three months of cash the contractor funded for free.
The habit
Log every instruction the day it lands, price it while the work is fresh, and reconcile the variation account against the certificate each month. The final account is only ever the sum of variations you kept on top of, one cycle at a time.
QScope prices each variation against the contract rates, tags it to the instruction that authorised it, and rolls the agreed value into the next interim certificate.