The final certificate, and why it can end your claims

All job long, the machinery was cumulative and self-correcting: an interim undervaluation simply came right in the next cycle, that is the design. The final certificate exists to switch that machine off. Somebody has to be able to say the account is closed, or jobs would stay arguable forever. The question is only whether it closes with your money inside.

What “conclusive” actually does

On many standard forms, once the final certificate is issued and a stated period passes without proceedings being started, the certificate becomes conclusive evidence of the matters your form lists: typically that the account has been finally adjusted, and on some forms that quality matters expressly left to the certifier’s satisfaction were satisfied. Conclusive means what it sounds like: an adjudicator or judge is not allowed to look behind it. The exact list and the exact period vary by form and edition, so this is a contract particulars question, and the answer is in yours.

Two consequences, one each way:

• Against you: the variation you never quite submitted, the undervalued line you meant to fight, the loss and expense you were saving for the end, after the window, gone. The account you were going to argue is now the account.
• For you: the client’s general complaints about the account close too. The certificate cuts both ways, which is the half people forget when they panic about it.

What it does not switch off

The payment machinery still applies to the money it certifies. On jobs the Construction Act covers, the final payment is still a payment: the notice rules run, and paying less than the sum due still needs a pay less notice in time (section 111). A client who treats the final certificate as an invitation to pay what they feel is right has the same problem they had in month three. And conclusivity provisions do not generally protect against everything: latent defects and liability questions live longer lives under the general law, which is one of the reasons the certificate’s exact wording matters.

Before it issues: the only cheap moment

Everything about this page is cheaper before the certificate exists. That means the account goes in complete, every variation, every adjustment, nothing “saved for later”, because later is precisely what conclusivity deletes. If the assessment comes back wrong, dispute it then, in writing, while everything is still provisional; a documented disagreement on the table changes how the endgame reads even if it ends up in the window anyway.

On a job for someone living in the house

Conclusivity is contract machinery, so it binds a homeowner job exactly as far as your form provides it, and on consumer terms an aggressive conclusivity clause in your own document can face the fairness test, another reason not to draft exotic ones. Where there is no formal certificate at all, the closing document is whatever you both sign, and anything headed full and final settlement does the same job by agreement: read it as carefully as this page reads the certificate. Disputes go via a letter before action and the county court, since a residential occupier is outside the Act (section 106).

What to do this week

1. Find your form’s conclusivity provision and its period, now, on the live job, and write the period into your close-out plan.

2. Sweep the account for anything unsubmitted and get it in before the final certificate machinery starts.

3. If a final certificate has just landed and you disagree with it, treat it as urgent: the window is running, and this is the week for advice, not for drafting one more polite email.

Where the information stops

What your certificate is conclusive about, and exactly when the window closes, are questions of your form’s wording where editions genuinely differ, and getting them wrong is irreversible by design. A disputed final certificate is a see-a-solicitor-this-week document, and that is the most concrete advice this page contains.