13-11 Vent below FLR

Question: 13-11Code Section: 7Date: 9 September 2013OBC 2012 Reference:

Question Submitted: What we have is a 3″ stack vent with an 1 1/2″ branch vent supplying air to a basement 3pc and a basement laundry tub, as well as an 1 1/2″ vent to a laundry box in which the vent is “looped” up and over the standing waste, flood level rim.

My question is: Is this legal as the vent connection is not over the flood level rim.

Note: Picture below, the 1 1/2″ abs vent through the floor is the branch vent off the stack vent, the TY to the right is the “loop” vent, the lower vent is going to the  basement laundry tub and the vent on the right is supplying air to the basement 3pc. The vents have a direction of flow so any condensation will drain away. The “loop” vent is draining into a TY on its side.

Interpretation: The Code Tech Committee agrees that this installation is not typical and should not be mistaken for a conventional rough in of a fixture.

The vent from the laundry box did extend above flood level rim with no possible way of condensation being trapped in the vent piping and there is no bypass created between the drainage and venting system.

That said, this installation could be accepted provided the situation the installer was presented with prohibited the use of conventional venting methods.

The term “loop vent” should not be deemed the name of this type of venting technique as this could cause confusion, however this is the term given in the diagram.

The relevant code references to consider for this installation would be, Drainage of Vent Pipes
(1) Every vent pipe shall be installed without depression in which moisture can collect. Vent Pipe Connections
(1) Every vent pipe in a plumbing system shall be installed so as to be direct as possible to a vent stack or open air, as the case may be, and so that any horizontal run below the flood level of the fixture to which the vent pipe is installed is eliminated where structurally possible. Connection of Vents above Fixtures Served
(1) Except for a wet vent, every vent pipe shall extend above the flood level rim of every fixture that it serves before being connected to another vent pipe.
(2) No vent pipe shall be connected in such a manner that a blockage in a soil or waste pipe would cause waste to drain through the vent pipe to the drainage system.