The primary difference is that there is some work that is still to be done on a building project, or maybe not. Substantial completion versus final completion is a concept of being “ready for intended use” versus being “fully finished”.Substantial completion is when the building or major construction projects are finished, and the essential systems – plumbing, electrical, HVAC, structure, etc – have been completed, so the owner can occupy or use the property. There are a few minor punch list items that may need to be addressed, however. Final completion is when the tasks that are still required to correct the issue and finishing have been finished. The contractor has, in general, provided the scope of work as agreed to in the contract at final completion (subject to the terms of the contract). Knowing these stages is important for an owner or contractor to know who is responsible for what, how they'll be paid, and what warranties they have, as well as what is involved in a project's closeout.