Determine when a sanitary backwater valve is required in a building drain (distinct from potable-water backflow prevention)

Steps

1. Scope this route to sanitary backwater valves at the building-drain level, protecting a building's own plumbing fixtures from public sanitary sewer backup — this is a distinct system and code chapter from potable-water backflow preventers, which protect the drinking-water supply from contamination; don't conflate the two.
2. Apply the core IPC rule (Section 715 in recent editions): fixtures with a flood-level rim, or a floor, below the elevation of the manhole cover of the next upstream manhole in the public sewer must be protected by a backwater valve installed in the building drain or the specific branch serving those fixtures.
3. Do not install a backwater valve on fixtures above that upstream manhole-cover elevation in new construction — check the code's exception language for existing buildings, which can differ from new-construction requirements.
4. Confirm the requirement against a surveyed elevation comparison (basement floor/fixture rim vs. the actual upstream manhole rim elevation), not a generic assumption that "basements need backwater valves."
5. Plan for an accessible cleanout/access cover for the valve per code and manufacturer instructions, since a valve that can't be serviced becomes a blockage point itself over time.