View Full Version : Basement Shower Wet Vent?

12-16-2008, 10:42 AM
Our house was built in 2003 with a partially finished basement. The current bath is a half bath, but when I pulled a copy of the blueprints they called for a 3/4 bath to be roughed in. The prior owner of the home was the builder and he moved next door. So I asked him where the shower stub was. He had planned on building a walk in shower behind one of the current 1/2 bath walls, but never completed it when they decided to build a new home. Anyways, he advised that the drain was covered by a piece of Dow blue and the slab was then poured over. He gave me the approximate location of where to find this, which is to be done at a later date.

My question is in regards to venting of this shower. My folks have a similar 3/4 bath and their's too I couldn't figure out how the the shower was vented. I contacted my local plumbing inspector and he asked if my lav was hooked into a 2" stub in the floor and then has a 1 1/2" reducer hooked to a vent. I said yes, the drain reduces to that size at a height above the lav trap. It than has a traditional vent running to the attic. His advice was that in my case and likely my parents was that the shower drain was sharing the vent for the lav, a "wet vent" he called it.

So the drain pipe is running horizontal to the lav drain stub? Is there a maximum length that shower drain pipe can run? My folks shower drain is probably 8' away from the lav stub and mine is probably running 8'. Of course I have no idea what the plumbing looks like under the slab, so who knows if there are wyes or T's involved prior to that 2" stub sticking out of the floor. The neighbor on the other side of me is also a builder and advised that his brother in law did the plumbing on my house, this individual is considered very reputable and the plumbing in the house looks good otherwise.

Thanks for your help.

12-16-2008, 06:14 PM
I'm also trying to find answers myself. I have found a number of references to horizontal draining and wet vents. In an answer to someone's question regarding a shower base, NHMASTER, answered that a 2" horizontal drain could be run 6' before needing a vent. Does this still apply to system that is supposedly wet vented?

If so, I'm feeling pinched as I would like to move my drain 15" further away from the current location. How can I prove to the plumbing inspector that I'm still within 6' if all the plumbing is buried in the slab?

12-18-2008, 05:46 PM
Have I posted this in the wrong forum? Someone please let me know if I should be in the Shower/Bath or Remodeling forum. Thanks.

12-18-2008, 06:12 PM
This is as good as the remodel forum...I don't know the answer, so I didn't answer. Many of the pros do skim all of the categories, so give it a chance.

12-18-2008, 09:18 PM
a 2" drain line running at a 1/4" slope can have the vent up to 8' from the trap.

The issue with wet vents is that they need to be sized larger than regular vents based on the DFUs.

Jay Mpls
12-18-2008, 09:37 PM
In MN you can be 5' from your vent and a basement wet vented *toilet* is allowed (Lav going in) Beyond that as code *here* speaks to your issue, JAR546 has what we have.
Sizing is usually a pipe size up for wet venting,simply stated.You may wish to contact you local plumbing inspector as to do the job once!
Merry Christmas all!

12-18-2008, 11:35 PM
To understand horizontal wet venting, you need to have a solid understanding of what section is the trap arm and what section is the actual wet vent. You need to ensure that the entire length of the wet vent is sized appropriately for the number of fixtures you intend to wet vent, and that the fixtures are placed properly along that wet vent. If you do that, then you can treat the trap arms as you would in any normally vented installation; meaning that you can run each trap arm to a maximum length designated by your specific code.

You can't just treat each trap arm like a wet vented branch and run it any length you like. If you need to run a longer trap arm than your code will allow for the size of pipe you are using, then you are forced to vent that fixture and change that long trap arm into a properly vented branch.

12-20-2008, 02:12 PM
Lurker, I think I understand what you are trying to say, but only because I have been in the business for a long time. A non-plumber will have absolutely no idea what you mean.

Here, and under many codes, 2" can run 5' and then you need a vent. That vent can be a "wet vent" with a lavatory above it, or it can be a dedicated dry vent for just the individual fixture. Until you find the shower connection under the concrete, you have absolutely no idea where it is connected or its distance to a vent.

12-20-2008, 07:56 PM
Thanks everyone for the replys. I have a better grasp from your help and reading other posts. My only explaination for the definite more than 5 feet but less than 8 feet of my shower drain (and observed install at my folks) is probably what Jar546 indicated. I did find the drain as indicated about 2.5 inches under the slab.

I think the best thing for me is to make a solid diagram, get all my dimensions on it really good, maybe take some photos and head over to my plumbing inspectors office. Show him what I have and let him know what I'm thinking of doing. He, the regular building inspector and electrical inspector have always been really approachable and willing to help in the past, so I should be okay.

Thanks again everyone. I home to be posting a question in the bath or remodeling forum soon about choosing a shower pan.

Merry Christmas, Happy Holidays, a Great Festivus to ya, or whatever greeting suits you best this time of year.

the coast of Lk Michigan, WI