Handover is the point at which finished work passes to the customer.
What it triggers
Final billing, or the last stage of it — see progress billing.
The start of the warranty period.
The release of any retained amount, usually after a further period.
Responsibility for the site and, frequently, for insuring what has been installed.
Because it carries all of that, what counts as completion belongs in the contract rather than being decided by whoever is on site.
The outstanding list
The short list of minor items agreed at handover — variously called a punch list or a snag list.
Two rules make it work. It is written and agreed at the walkthrough, not added to afterwards. And it is short and dated, with each item having an owner and a date, or it becomes an open-ended reason to withhold payment.
An unresolved list is one of the most common causes of a final invoice going unpaid.
Commissioning
For installed systems, the process of bringing them into service and demonstrating they perform as specified — testing, balancing, recording settings.
It is the evidence that what was installed works, and it is what a defect claim is later measured against.
What the customer should leave with
Documentation for what was installed, warranty details, any certificates required by the trade, and a clear statement of what is covered and for how long.
Handing this over at completion rather than on request is the difference between a professional close and a series of follow-up calls.
The defects period
A period after completion during which the business returns to correct defects at its own cost. It is distinct from a warranty on the equipment, and the two frequently run for different lengths.
Its cost is real and belongs in the price — see warranties and guarantees.