Moving Shower Drain to center of floor

[PAB]

I'm hoping someone can help me here. I'm currently remodeling my bathroom and the plumber I usually use is busy right now and has asked me to call him later. In the meantime, I'd like to see if this is something that is doable and, if so, if it is something that I can try. Hope I get the terminology correct.

My shower drain is currently offset from the center of the floor (width wise) by 18 inches. I would like to have it moved to the center of the floor. Although it isn't necessary, I see this as making future work easier.

If the drain is moved to the center, the drain would be only 6 inches away from the current location of the vertical PVC pipe. That is too close for a p trap, as far as I can tell.

Could I extend the vertical portion of the drain further to the right, thus giving me room to install a p-trap at the desired location?

Hope this makes sense. I've posted some pics to help.

Appreciate your help.

 

[wwhitney]

Your bigger problem is that your shower is not vented, so you need to correct that now. Determining the easiest way to do that would require seeing all the bathroom DWV pipes and knowing which ones are dry vents.

Cheers, Wayne

 

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[PAB]

My apologies. The picture above where I said "main drain" was actually a pipe that vented through the roof. It has a second branch for the toilet drain and then goes between the joists, between the studs, and up through the attic into the roof. Hopefully this is correctly done. I'll post some pics.

 

[wwhitney]

In your first new picture, I can't really see the configuration of fittings at the bottom of the photo, down below.

But this doesn't change anything in my previous post--the shower vent needs to come off the trap arm within an elevation of 1 pipe diameter of the trap outlet. The shower drain can't drop down 6" and then have a vent taken off. So you need to make some further changes to fix your venting.

Cheers, Wayne

 

[PAB]

Thank you Wayne for your reply. After your reply, I've done some research. Part of which was to determine the difference between dry and wet vents.

Would you think that this bathroom was vented with a horizontal wet vent? If so, I'm assuming based on your post that there are still considerable problems with it. For one, it would appear (to me) that the toilet is in the middle of the system which I believe is a no-go. Also, as you say, the shower drain pipe goes down into the vent rather than being attached almost horizontally into the vent.

I've attached a few more pics to show my setup. Hopefully it is clear based on the pictures. In addition, I've posted a pic from the 2015 Michigan Residential Code. This pic seems to show (to me) that the trap arm can be up to 36" higher than the attachment to the vent. Based on my other research this doesn't seem right, but I don't see why.

 

[wwhitney]

That code snippet is very interesting, but it's a Michigan only amendment. Are you in Michigan? Also, it requires the vertical leg to be 2-1/2", and the horizontal leg to be 3", which is not the case in your installation. It's also shown with a dry vent takeoff, which is not what you have.

Can you indicate where along the current upper shower trap arm you'd like the shower drain to end up? If it's over the area where the pipes currently turn downward, you may be able to lower your p-trap and tie into the WC/lav drain on the horizontal for a normal horizontal wet vent.

Also, what's the 3" (?) pipe just below the shower in your last photo? Does it join up with the shower drain and the WC/lav drain down below in the hard to see area?

Cheers, Wayne

 

[PAB]

Thanks again Wayne for your reply!
Answer a couple easy questions first.
I am in Michigan.
You're right - the pipe from the shower that ties into the main drain would need to be 1 pipe size bigger than the trap arm and it is the same size. I didn't see that.
The pipe just below the shower ties in (in the attic) to the other (horizontal) pipe that the shower, toilet, and sink drain into. Pics included.
If you look into the pictures in the first post, you'll see the desired location for the shower drain. It is very close to where it ties into the main drain, so that sounds promising.

Now a couple of questions based on this.
Can it be a proper wet vent with the toilet in the middle and attached as it is?
I think you're talking about making the shower p-trap drop a lot lower so that where it attaches to the main drain it is a mostly horizontal pipe (similar to the way the toilet attaches to the main drain). Is that correct? I've attached a couple pics that will show what I'm dealing with down there hopefully a bit better. It's a little cramped but at least there's no subfloor that has to be stripped away now.
I've also attached a pic of the other drain that you mention in your post above (beside the shower). Perhaps that might be something that could be linked into the shower drain for venting instead?

Finally, a bit off topic, if the wall with the pink insulation is attached to an interior wall, and it's going to have the shower wall, is there any reason (except for perhaps sound) for keeping it in there?

BTW, while I'm determining more and more that this is a job for a plumber (unless you disagree with how easy this should be now), you have certainly helped me understand this a lot more so that I know some options when he comes over. Thank you.

 

[wwhitney]

Thanks again Wayne for your reply!
The pipe just below the shower ties in (in the attic) to the other (horizontal) pipe that the shower, toilet, and sink drain into. Pics included.

But the cast iron doesn't tie into the shower or WC/lav drains that you can see? Then that pipe is likely a vent for lower levels. Which means that it's not useful for this floor's plumbing, it's just another obstacle.

Thanks again Wayne for your reply!
Can it be a proper wet vent with the toilet in the middle and attached as it is?

The WC being in the middle isn't a problem, the IPC allows that. The challenge is the geometry, the space in the lower floor soffit (?) is quite tight. Working there may require access from below. I'm not sure how to fit the necessary connections in there around the cast iron and the air duct, but perhaps someone on site will be able to figure it out.

Thanks again Wayne for your reply!
Finally, a bit off topic, if the wall with the pink insulation is attached to an interior wall, and it's going to have the shower wall, is there any reason (except for perhaps sound) for keeping it in there?

No, just for thermal or sound insulation. [Or if the other side of the wall were a different dwelling unit, it might be required for the proper fire rating between the two units.]

Cheers, Wayne

 

[wwhitney]

I'm not sure how to fit the necessary connections in there around the cast iron and the air duct,

I guess you might be able to fit a 3"x2" combo into the 3" drain line between the 45 and the 90 where it turns downward. And then you might be able to connect the shower trap outlet directly to the combo, using a pair of 45s on the drain tailpiece if necessary to hit the trap. That's my best idea, but it's all very tight.

Cheers, Wayne

 

[PAB]

Thanks Wayne for your help.

The Cast Iron pipe doesn't tie into anything on the 2nd floor. The cast iron is the main drain pipe. In the basement the PVC drain for the bathroom we're discussing ties into it. I've attached a pic of the basement where this happens. Both pipes tie-in again in the attic before going out through the roof.

Regarding your comment, I thought you could tie into a vent from another floor if it is above the fixture line (something like 42")? I really don't know how that would be done in the case of the shower and the cast-iron vent that continues (as PVC) beside the shower drain, but thought I'd throw that out there. I was thinking I could do some kind of re-vent in the wall (at least 42" high and behind the shower drain), but that is very confusing to me when using the p-trap and drain for the shower. I'm probably using completely nonsense language for plumbing, but hey - that's why i'm trying to learn on this forum!

FYI, there is also another tie in on the cast iron (in the basement) for the bathroom on the main floor. There are two stories, with a bathroom on both the main floor and 2nd floor. The bathroom we're discussing on this forum is on the 2nd floor. Doubt that adds anything but figured I'd mention it.

Regarding the toilet, I've read that having it not be the last item on the wet vent, and flushing it, can cause it to pull water out of the trap of other fixtures. As usual, I'm assuming I'm wrong and have simply misunderstood, but thought i'd mention this just in case.

One more thing - if you have any link to a 3x32 combo (again my plumbing lingo isn't great), that would be appreciated. Thanks again for your help!

 

[wwhitney]

Regarding your comment, I thought you could tie into a vent from another floor if it is above the fixture line (something like 42")?

You can combine two vents at an elevation that is at least 6" above the flood rim level of any of the associated fixtures. 42" comes from the idea that one of the fixtures is a lavatory with a 36" counter.

That doesn't help you vent the shower, though, as you can't tie into the cast iron vent in the floor, that's not 6" above the flood rim. And you also can't go horizontal at an elevation less than 6" above the flood rim. So the only options for venting a shower are wet venting (or related allowances like circuit venting), and running the drain under a wall for a vertical dry vent takeoff.

Regarding the toilet, I've read that having it not be the last item on the wet vent, and flushing it, can cause it to pull water out of the trap of other fixtures. As usual, I'm assuming I'm wrong and have simply misunderstood, but thought i'd mention this just in case.

I don't actually know how it would perform, I don't have the experience. I just know that the UPC requires the WC to be last on the wet vent, but the IPC (Michigan) does not impose that condition. From which I infer that the code writers for the IPC decided that was unlikely enough not to be a concern.

One more thing - if you have any link to a 3x32 combo (again my plumbing lingo isn't great), that would be appreciated.

Here's one, I haven't checked other vendors:

https://www.supplyhouse.com/Spears-P502-338-3-x-3-x-2-PVC-DWV-Wye-and-45-Elbow-Combo

Cheers,
Wayne