What notice periods apply under JCT contracts?

JCT's unamended forms are gentler on notice than their reputation. The payment notices carry the hard statutory deadlines: the Payment Notice window after the Due Date and the Pay Less Notice deadline before the Final Date For Payment, with the exact periods set by the particular form and its contract particulars. The progress side is softer in the standard text: the contractor notifies delay when it becomes reasonably apparent and applies for loss and expense as the need becomes apparent, duties written as promptness rather than as conditions with cliff edges. The danger is that almost no JCT subcontract is signed unamended. Schedules of amendments routinely convert those soft duties into hard ones: notice within a fixed number of days as a condition precedent, the legal term for a step that must happen before the right exists at all, often with fully priced applications required inside fixed windows. So the honest answer to what notice periods apply under JCT is: the statutory payment deadlines, always; and for everything else, whatever your schedule of amendments made them, which is why the schedule is the first thing to read, not the standard form summary.

Say a mechanical subcontractor on an amended JCT form assumes the standard text applies: notify delay when apparent, apply for loss and expense in due course. Its schedule of amendments, page 40 of 60, has quietly rewritten both: written notice within 10 days of each delaying event as a condition precedent, and a priced loss and expense application within 21 days. Four months of design churn later it submits one combined claim and is met with a list of dates it cannot cure. Nothing in the JCT badge on the cover protected it; the schedule was the contract. The lesson is that under JCT the question is never what the standard form says, it is what yours says.