Substantial completion is the contract milestone at which the project is sufficiently complete that the owner can occupy or use the space for its intended purpose, even if minor punch list items remain. It is typically certified by the architect or owner's rep through a formal walk-through and signed certificate of substantial completion.
Substantial completion triggers significant contractual events: the warranty period typically begins, retainage may be partially released, the contractor's obligation to maintain Builder's Risk insurance often ends, the owner takes responsibility for utilities and security, and the deadline for punch list completion starts. Disputes over whether a project is actually substantially complete (vs final complete) are common close-out friction points, especially when retainage release and contractor exit are at stake.