View Full Version : I want to properly vent a remodeled basement bath

12-26-2012, 07:43 PM
Hello, guys. I've spent a lot of time reading the posts on your forum and your adviced seems really top notch. I need help with properly venting a basement bath.
There was a wc & sink that were tied directly into the main drain. Neither were vented. We are moving the fixtures and adding a shower. Does my toilet need to be vented since it is so close to my main stack? I could do it easily, but I've read that given the distance to the stack, it doesn't need to be vented.
I am running a vent from the shower next to the exisiting stack. I was going to run it up to 6" above the overflow level of the sink directly above, then connect an AAV rather than have to tie into the cast iron stack. Will that work?
My biggest problem is venting the new sink. It will sit directly below the middle of a bedroom. Can I run a horizontal vent over to the stack? It would have to go around a corner. Can I install an AAV 4" above the drain line? The sink is about 6'6" from the main drain. Any advice would be really appreciated. Thanks so much.

12-26-2012, 09:08 PM
You cannot run the shower vent below the floor.

The shower vent and the lav vent must be vertical until they are at least 42" above the floor. Once they are above that point, only then can they run horizontal. (You still have to maintain pitch so that any liquid in the vent runs to the drains.)

They can be connected together and routed up next to the stack to their connection point, which must be at least 6" above the flood rim of the highest fixture connected to the stack.

It might be possible to wet vent the shower through the lav if it is close enough. In any case you have to have a proper dry vent for the lavatory before you can consider it.

12-27-2012, 06:59 AM
The toilet is below the one for the upper level so the "proximity to the stack" does not apply. It needs its own vent, and it should NOT be an AAV. If you use AAVs for the sinks they only have to be 6" above their connection to the drain, but since this is a lower level bathroom, they are NOT a good option for venting, regardless of how high the AAV is installed. The shower is not properly vented because the vent is horizontal below the floor. What is that thing with the round black cover? Is it a backwater valve or the old toilet location? If it is a BWV, then it is in the wrong location and you should rethink the entire design, or have a plumber design and install it.

12-27-2012, 08:11 AM
Ok, so let me see if I have this right. I need to vent the toilet, which isn't a problem. I must run the lav and shower vents vertically for 42" before I can run them horizontally, then I can connect them and run them to the 2" vent next to the stack. I should tie it all into the stack 6" above the flood rim of the highest fixture. Don't use AAV's anywhere. Can I wet vent the shower thru the lav? They are about 5' apart.

The black thing is the old toilet flange.

12-28-2012, 09:33 AM
Under my state's plumbing code, I would be allowed to wet wet the shower through the lav, as long as the vent is not further than 96" from the trap. (Measuring the trap arm's length) and the wet vent section does not exceed 1/4" per foot.

Your municipal plumbing inspector might advise you if you cannot find the details in your plumbing code.

12-28-2012, 03:43 PM
I'm thinking it would just be easier for me to turn the shower trap 90* toward the stack and run a vent to the wall, then up. The only problem I see is getting my 90* fitting over the footing. I'm afraid it will be in the way of the shower pan. Can I run the shower vent to the new 2" vent instead?

12-28-2012, 04:04 PM
Once a pipe becomes a drain, it can no longer be called a vent. I'm assuming that stack is the drain from the fixtures above. In order to vent things, you need to go ABOVE the fixtures that drain is servicing by 42" or 6" above the flood plane of the highest fixture, whichever is higher.

12-28-2012, 05:24 PM
Yes, thanks. The red line running up next to the stack is a new 2" vent. I'll tie it in upstairs 6" above the overflow level of the sink, which is my highest fixture. I might actually connect it even higher since I'll be going thru a wall that has a wallpaper border about halfway up.

12-28-2012, 06:02 PM
Ok, so I think I have to replace the sani-t in the picture with a wye, but otherwise does this look like it will work?



12-28-2012, 07:22 PM
I think you are having trouble with the term vertical. No part of the vents can be piped horizontally under the floor. Each trap's vent must rise vertically from it's connection on the trap arm. Vertically means straight up and down, but it is ok to angle a portion of the vent no more than 45 degrees if it is necessary.

Here is a nice link to Bert Polk's plumbing tips (http://www.co.lincoln.or.us/planning/plumbing/apps/plumbingguide.pdf)

12-28-2012, 08:44 PM
Thank you very much for the diagram. It is really helpful. The only thing I'm confused about is that the vent has to run horizontal under the shower pan to get clear of it before it runs vertical. I am running a 2" vent up behind the existing stack, but I have to get the vent from the trap to the new vertical vent somehow. Do I need to run the vent straight to the wall, then up 42" before I can tie into the new 2" stack? I was trying to tie them together below the floor to avoid trying to put a 90* right over my footing. I could try to do that with both the shower and the toilet. Would that solve the problem?

12-29-2012, 09:21 AM
You have the right idea.

Route the drains so that the vents rise vertically into where a wall will be. They must be at least 42" above the floor before you go horizontal, and you already know you have to go above the fixtures on the upper floor to make the vent connection. All the horizontal drains and vents must be pitched 1/4" per foot.

This picture is not quite right for you, but should impose the right idea. The length of the entire wet vent is measured, not just the trap arm. Maybe one of the plumbers who works under IPC can post exactly how long the wet vent can be there in MI.

You might need to think a little outside of the hole you have dug.


12-29-2012, 10:46 AM
Wow, that is great! Thank you so much for all the time you've taken to help me. I wish I had read your reply before I broke up more concrete (I feel like I'm getting really good at that). Here's what I did, but it looks like it would be easier to do it the way you drew it. I'm going to run the lav vent exactly the way you have it pictured.

For some reason the website is not letting me upload my pictures. I'll keep trying, but basically I ran the shower vent to the concrete wall and straight up to 42", then I'll turn right and run it to my new 2" stack. There's a window directly above, but running it up to 42" works just fine. I could run the toilet vent the same way because I will have to bust up less concrete than taking it to the wall to the right.

I'm concerned about getting the 90* over the footing properly. I'm going to try to upload my pictres again so you can see what I mean.

Thanks, again.

The only way I can get the pictures up is to add a link to them here:

https://sites.google.com/site/deeannuhlarik/home/Bath3 copy.jpeg (https://sites.google.com/site/deeannuhlarik/home/Bath3 copy.jpg)

https://sites.google.com/site/deeannuhlarik/home/Bath4 copy.jpg

12-29-2012, 10:59 AM
one of your photos shows a san tee on the horizontal. that is a no-no. A horizontal connection is made with a wye or combo

12-29-2012, 11:12 AM
one of your photos shows a san tee on the horizontal. that is a no-no. A horizontal connection is made with a wye or combo

Yes, thanks for catching that. I didn't have a spare wye so I laid a sani-t in there for the picture. :)

12-29-2012, 11:36 AM
When trying to get up over the edge of the footing, you can cut a notch in the footing and/or come out the the floor at a 45 and then back to vertical in the wall. If you use a 90, you are making a flat vent, which is a no-no.

12-29-2012, 11:48 AM
Ok. Is there any danger to cutting a notch into the footing? I'm thinking no because you're advising it and it would be a very small section of footing.

12-29-2012, 02:09 PM
I would try to avoid it, but others seem to do it without any hesitation.

An alternative would be to bump the framed wall in a few inches (moving the shower with it) so that there is room to run the pipe up at a 45 past the edge of the footing and still come into the wall.

edited to add- the flat section of vent in your linked photo is still not going to cut it. Vertical, down to 45 degrees is ok. No less.