Long-lead items are materials or equipment whose lead time is long enough that they affect the project schedule if not ordered well in advance. The threshold varies by project, but anything over 12 weeks of lead time typically gets flagged. Common long-lead items: structural steel (16 to 24 weeks), custom millwork (12 to 20 weeks), elevators (20 to 40 weeks), generators (24 to 60 weeks), main switchgear (16 to 50 weeks), transformers (40 to 80 weeks during supply disruptions), custom curtainwall (16 to 24 weeks), and specialty MEP equipment.
The long-lead list should be developed during preconstruction. Each item has a "must order by" date back-calculated from required on-site delivery. The owner approves early procurement for each, often before the drawings are 100% complete, accepting some scope risk to protect the schedule. The procurement log tracks each item from PO through fabrication, shipment, and delivery. Long-lead items missed during preconstruction are a top three reason commercial projects deliver late.