In vertical wet venting, when two wall outlet fixtures are on the same floor level with their drains connecting to the same vertical drain at different elevations, the lower fixture drain may be wet vented only if which condition is met?

• A. No other fixtures may discharge into the vertical drain above or below the two fixtures
• B. Any other fixture may discharge into that vertical drain
• C. Only above the upper fixture
• D. Only below the lower fixture

Answer: (A)

Vertical wet venting relies on a vertical drain acting as a vent for the fixtures connected to it. For the lower fixture to be wet vented, that vertical drain must be dedicated to just those two fixtures along that section; no other fixtures may discharge into it either above the upper connection or below the lower connection. If another fixture drains into the same vertical line, the vent path can be disrupted, leading to siphoning of the traps or reduced venting effectiveness. Keeping the vertical drain free of other connections ensures the vent can properly provide air and prevent trap siphonage for the two fixtures.