In vertical wet venting, which condition allows the lower fixture drain to be wet vented?

• A. Two wall outlet fixtures on the same floor level with their fixture drains connecting to the same vertical drain pipe at different elevations
• B. When there are two fixtures
• C. When there are more than three fixtures
• D. When the fixtures drain into separate vertical stacks

Answer: (A)

Vertical wet venting relies on a single vertical drain acting as both a drainage path and a vent for fixtures that tie into it at different heights. When two wall outlet fixtures drain into the same vertical drain pipe at different elevations on the same floor, the vertical stack provides the vent path between the connections. This lets the lower fixture drain be vented by the air in the vertical pipe as the upper fixture drains, preventing siphon and allowing proper drainage. If fixtures don’t share a common vertical vent path, or if they drain into separate stacks, there’s no vent to use, so wet venting isn’t possible.