I am planning to finish the basement and have some questions regarding the plumbing.

The builder already have the bathroom rough in but the location is at middle of the basement. I want to have the bathroom located in a corner. This rough in vent is the only one that I believe that I can use, unless I go with "wet vent" method.

Unfortunately this pipe is about 20 feet to the corner. So my question is: is it OK to extend this pipe 20 feet horizontally the connect it to bathroom toilet, shower and sink?

I am also planning to move the laundry room to the basement. In order to use the vent pipe, the branch to the laundry will have to go up to the ceiling first, the go down. Is it OK?

| vent
|      |---------------------------------+
+------|                                 |-> laundry
+ -----------+
             |----------> bathroom

Consider an Air Admittance Valve, rather than a traditional vent, in this situation. The downside is these are mechanical devices that in theory can fail. The upside is reduced sewer venting to the atmosphere and less pipe.

Buy a quality one: there are $3 models that are not the same thing. Look for a series of certifications for this task and expect to spend at least $30.

AAV Plumbing

A vent that goes up and then down is not OK. AAV's are approved in the International Plumbing Code, and the USA National Plumbing Code.


All building, plumbing, and electrical codes should be assumed to have local variations from the national code. Air admittance values are allowed in some circumstances, by some jurisdictions, but not in others. In many (most?) cases they are only allowed when it is not possible to install a regular vent, such as a kitchen island. I believe that in general you may run a horizontal vent any distance, but the size of the vent is determined by how many units it is venting. And no, it may not go down then back up. Although is is mostly carrying air, it does have to be able to drain any rainwater that enters.

The answer to these types of questions is always "check with you local inspector", not whoever responds on the Internet.

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