On a commercial tenant improvement, plumbing is not a big share of the budget — but it is almost always the first trade with work on the critical path. Sanitary and vent lines go underground before the slab, water and gas rough-in goes in the walls before drywall, and both are inspected before anything closes over them. Miss the sequence and you are cutting concrete or opening finished walls to correct it.
The work that gets buried
- Underground sanitary and vent — trenched and set to grade before the slab is poured. Slope, cleanouts and pipe size are fixed once the concrete goes down.
- In-wall water and gas rough-in — supply lines, stub-outs and valves, set before drywall.
- Above-ceiling mains and risers — routed before the grid, coordinated with HVAC, electrical, fire sprinkler and structure.
Inspections that gate the schedule
- Underground / under-slab — with the lines on test, before backfill and pour.
- Rough-in / top-out — DWV and water piping on test, before drywall and ceiling cover.
- Final — fixtures set and trimmed, backflow tested, water heater and gas connected, tied to the certificate of occupancy.
Each of these is a hold point. The slab does not get poured, and drywall does not get hung, until the preceding plumbing inspection passes. A failed inspection is not just a re-inspection fee — it is every trade behind us waiting for the next available slot.
What keeps it on track
- Fixture count, locations and equipment cut sheets confirmed before underground layout — not after.
- Long-lead items — grease interceptors, water heaters, backflow assemblies — released early.
- Above-ceiling coordination done on paper before anyone is in the field.
- Inspections booked the moment the work is provably on test, not optimistically.
Done this way, plumbing is the trade that lets the slab pour on schedule and the walls close on schedule — instead of the one everyone is waiting on.