What is the defects period after a build?

New buildings move: they dry out, they settle, and their faults introduce themselves over the first months of living there - the crack above the lintel, the door that sticks in weather, the joint that opens as the heating cycles. The defects period exists for exactly this: a stated run of months after handover during which faults in the builder's work are the builder's to come back and fix, at no cost to you, with the last of the retention held as the reason to actually do it. The period only works if it is run in writing: each fault logged when it appears and notified to the builder in writing the same week, kept on one list with dates and photographs, and swept up in a final walk-round booked a month before the period ends. What the period does not cover is wear, misuse and the things you have changed yourself - which is another reason the written log matters.