Rearranged Bathroom Drain & Vent

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me1483

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Good evening. I've tried to work out the best way to drain & vent my rearranged & remodeled bathroom, but all the ideas I've come up with won't work for one reason or another. I'm hoping to get an easier way than the one I finally settled on.

First, here's my bathroom as it was when I bought the house. Forgive the crude Paint drawing of the plumbing.

Bathroom Before.png


Shower to the left, water closet in the center, lavatory to the right. Pipes under the floor are red, vertical pipes are green. The lonely green circle next to the 3" stack is venting from basement & first floor fixtures, it joins the stack maybe 3' above the bathroom floor. Of course the green circle behind the sink is the sink's vent. If I understand things, the pipe heading from the shower's trap was the trap arm, vented via the sink vent making the pipe from the sink to the WC a wet vent for both the WC and shower. The 2" pipe joins to the 3" on the side of the elbow. Picture attached.

The new bathroom layout:

Bathroom After.png


The lav and shower are switching places so as to gain a larger shower. I've cut and temporarily plugged the drain pipe where it comes off the WC and the vent pipe in the wall. Floor joists (2x10) run parallel to the long wall. There'll be a medicine cabinet recessed in the built-out wall behind the mirror. The long wall behind the WC is spaced from the block wall (common with townhouse next door) by a couple inches, not sure of the exact measurement.

So, what's the best way to drain & vent the lav & shower in their new locations? Also probably have to vent the WC, but likely that would happen as part of the venting of the rest. I'm willing to go into the attic and remove the old vent in the wall if needed but I'd prefer to use it if possible. The shower drain location is flexible, though typical shower design would tend to keep it toward the center.

Thank you in advance.
 

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wwhitney

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Virginia uses the IPC, so my comments are based on that.

The lavatory is going to need a vent at the elevation of its trap, either a dry vent or an AAV. For the former you'd need to run the dry vent up the wall behind the vanity and across the ceiling to tie into the stack in the attic. The san-tee for the lav trap arm could be off center, so the lav vent can rise up to one side of the medicine cabinet. Then the trap arm can either exit the wall off center, or you could turn the san-tee so the side inlet is parallel to the face of the wall, and use a quarter bend to bring the lav trap arm out of the wall where you want it.

Then the existing dry vent behind the original lavatory location is only useful if you want to dry vent the shower, in which case you'd route the shower drain to under that location, and pull the dry vent off with an upright combo, i.e. a combo with the barrel horizontal and the side entry vertical. [The IPC would allow you to use a san-tee on its back for that dry vent takeoff, but unless you are challenged for space, stick with the combo.]

But you don't need to dry vent the shower, you could wet vent both the shower and WC as was previously done. For this, the IPC doesn't care which order the fixtures join the lav drain, you could do lav, then shower, then WC, or lav then WC then shower. What is not allowed is to join the shower and the WC together before either one joins the lav.

And the shower trap arm becomes the drain portion between the trap outlet and the wye where it joins the lav drain. [i.e. the length and configuration of the lav drain upstream of that wye is immaterial to venting the shower.] That trap arm is limited to one pipe diameter of fall, while it must fall at least 1/4" per foot. So for a 2" pipe, you have up to 2" of fall, and can therefore achieve a length of up to 8' if you get the fall at exactly 1/4" per foot.

Lastly, where the WC joins the lav drain (before or after the shower), it is best practice not to have the closet flange directly over the horizontal drain (in which case the WC would drop into an upright combo). Rather, it is typical to have closet flange - closet bend (90 elbow) - horizontal wye (all entries at 2% slope) to join the lav drain. If your project is subject to the plumbing portion of the IRC (based on the IPC but with a few differences), then the upright combo configuration is prohibited; if it is subject to the IPC itself, then the upright combo configuration is allowed, but dispreferred.

Cheers, Wayne
 

me1483

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Thanks for the reply, Wayne. Dry venting the lav was the answer I finally landed on; I'm glad for confirmation it's the right one.

The lavatory is going to need a vent at the elevation of its trap, either a dry vent or an AAV. For the former you'd need to run the dry vent up the wall behind the vanity and across the ceiling to tie into the stack in the attic.

I'd like to avoid as much attic work as possible. The lav backs up to an exterior wall, meaning the attic is about as small as it gets there. Would it be possible to run the dry vent horizontally behind the long wall once it's at least 6" above the lav's flood rim? (Pretty sure I'm allowed to angle the vent up to 45 degrees to get past the medicine cabinet before going horizontal.) It would then tie to the stack behind the bathroom wall. Or is an AAV the preferred venting method here? AAV is by far easiest to install but may have downsides I'm not aware of. <edit>In this case can the AAV live inside the cabinet or does it need to be above the lav's flood rim?</edit>

Then the existing dry vent behind the original lavatory location is only useful if you want to dry vent the shower, in which case you'd route the shower drain to under that location, and pull the dry vent off with an upright combo, i.e. a combo with the barrel horizontal and the side entry vertical.

I'm not sure this would work; I'd need to measure carefully to determine whether there's enough room for 1/4" slope if I were to U-turn the shower drain like that. I'm content wet venting the shower and cutting the old dry vent out.

Lastly, where the WC joins the lav drain (before or after the shower), it is best practice not to have the closet flange directly over the horizontal drain (in which case the WC would drop into an upright combo). Rather, it is typical to have closet flange - closet bend (90 elbow) - horizontal wye (all entries at 2% slope) to join the lav drain. If your project is subject to the plumbing portion of the IRC (based on the IPC but with a few differences), then the upright combo configuration is prohibited; if it is subject to the IPC itself, then the upright combo configuration is allowed, but dispreferred.

I'm not confident I'm tracking this. I think you're saying that the existing elbow (of the type pictured below) is no longer allowed/preferred.

iu


Instead, the preferred connection would include a wye such as this:

iu


Do I have that right? In which case, the final configuration would be something like this?

Bathroom After 1.0.png


Again, pardon the bad Paint skills. The green vent behind the lav either represents an AAV or a dry vent. WC pipe is 3", all other pipe is 2", drawn size notwithstanding. The dual 45s in the WC pipe are to create room for the horizontal 3x3x2 wye + 45. Another picture of the existing WC pipe is attached to illustrate space constraints. The wires in the picture can be moved; they're not connected and there's plenty of slack. I would install additional pipe hangers as there are none presently. Code must have been different in the 70s.

One other question. All the existing pipe is ABS, which I've been unable to easily source. Seems like they only carry PVC though I haven't looked really hard yet. I was planning to use no hub couplings, the reinforced ones, for PVC to ABS joints since there's no code-approved glue (Home Depot availability aside). If I end up modifying the 3" WC pipe is a reinforced no hub coupling still the preferred method or should I try harder to find 3" ABS?

Thanks.
Phillip
 

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wwhitney

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I'd like to avoid as much attic work as possible. The lav backs up to an exterior wall, meaning the attic is about as small as it gets there. Would it be possible to run the dry vent horizontally behind the long wall once it's at least 6" above the lav's flood rim?
Yes, you could wrap the vent around the walls if you prefer. Once 6" above the lav's flood rim, the vent can go horizontal; below that elevation it has to be at least 45 degrees above horizontal.
Or is an AAV the preferred venting method here? AAV is by far easiest to install but may have downsides I'm not aware of. <edit>In this case can the AAV live inside the cabinet or does it need to be above the lav's flood rim?</edit>
AAVs are certainly easier and allowed under the IPC. You will get different opinions on whether they are good enough or whether a dry vent is worth the extra trouble. The AAV can live in a vanity under the sink, as long as it is at least 4" above the trap arm
Do I have that right?
Yes, that's right, but the way you've drawn it is more convoluted than necessary.

First, if you were to bring the lav/shower into the WC via that joist bay, the way to do that would be to replace the quarter bend with side entry with a regular closet bend (a quarter bend or a reducing closet bend). Then the 3" 45 just downstream of the closet bend would become a 3" wye, and the shower/lav would enter via the straight inlet.

But, you don't have to join the lav to the shower before they both join the WC. You could just bring the lav into the WC drain per the above. And then cut in a 3x3x2 horizontal wye farther downstream to bring the shower in there. That would let you eliminate a quarter bend in the shower trap arm by starting it out directly up the page, rather than starting it out to the left. (Although if there's some obstacle that would make the routing you've drawn preferrable, that's OK as long as you comply with the maximum 2" drop rule on the 2" shower trap arm.)

On ABS vs PVC, if you want to use PVC for the new work, that's fine. I'd suggest cutting back the 3" ABS as far downstream as necessary and just redoing everything upstream in PVC. To connect 3" PVC to 3" ABS, use a Fernco 3005-33 or Mission P-300. If you dry vent the lav, you'll also need to cut into the ABS to connect the PVC vent, which might require up to (3) similar couplings. Although in smaller sizes the series number may not be 3005, just make sure they say "Plastic to Plastic".

Cheers, Wayne
 

me1483

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Again, thanks for the info.

Yes, you could wrap the vent around the walls if you prefer. Once 6" above the lav's flood rim, the vent can go horizontal; below that elevation it has to be at least 45 degrees above horizontal.

Most likely I'll install an AAV, unless someone else gives me a compelling reason not to. If I dry vent I'll go via the wall and keep the vertical requirements.

I'm all about convoluted. :) I see what you're saying about the 3" wye + adapter bushing replacing the 45 and will install it that way. There's a vent van for the first floor bathroom that makes routing the shower directly to the WC difficult. Plus I'd like to not have to cut another hole in my joists. It looks like the trap arm from the shower will be about 6', unless the quarter bend adds more distance than its actual dimensions. I think that mostly applies in pressurized supply lines, though.

On ABS vs PVC, if you want to use PVC for the new work, that's fine. I'd suggest cutting back the 3" ABS as far downstream as necessary and just redoing everything upstream in PVC. To connect 3" PVC to 3" ABS, use a Fernco 3005-33 or Mission P-300. If you dry vent the lav, you'll also need to cut into the ABS to connect the PVC vent, which might require up to (3) similar couplings. Although in smaller sizes the series number may not be 3005, just make sure they say "Plastic to Plastic".

I'll pick up one or more of those couplers. I'm assuming I can't just cap and abandon the old dry vent; if not I'll need a couple more couplers to properly remove it without changing the height of the stack pipe above the roof.

Is it normal on this forum to post during and after pictures? I know those are helpful on the John Bridge tile forum.
 

me1483

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Am I correct in thinking that I can use a short radius elbow, what Home Depot sells as a vent elbow, for the transition from horizontal to vertical beneath the lav and upstream of the AAV? I'm aware that I have to use a larger radius when I go back to horizontal under the floor.

Thanks.
Phillip
 

wwhitney

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Am I correct in thinking that I can use a short radius elbow, what Home Depot sells as a vent elbow, for the transition from horizontal to vertical beneath the lav and upstream of the AAV? I'm aware that I have to use a larger radius when I go back to horizontal under the floor.
Surely you mean downstream of the AAV? The easiest way to do an AAV for a lav is to have the AAV in the vanity (at least 4" above the trap arm). Plus the trap arm can't turn downward until after it is vented.

As to the elbow, there are 3 types: vent (where the hubs are actually touching at the inside corner), quarter bend, and long radius. A vent elbow is never used for drainage, and is only used for vents when you have an extreme space constraint. For drainage, a quarter bend can be used when the outlet is vertical; otherwise use a long radius. [The IPC actually has some additional allowances for quarter bends, but unless you have a space constraint, stick with the above.]

Cheers, Wayne
 

me1483

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I do mean downstream of the AAV, it just came out upstream. :)

I need to research the precise differences between the quarter bend and long radius so I can figure out which one Home Depot sold me. I I only remember seeing the regular ell and the vent ell (which will be added to the return stack).

Thanks.
Phillip
 

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me1483

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Thanks for the links. However, my local store doesn't carry ABS so I bought PVC.

Looks like I got some of these two elbows:


Neither say they're long turn elbows, so either should work for the horizontal to vertical behind the lav. This one does:


It sounds like it'll work for the vertical to horizontal from the lav beneath the floor. It also claims to be in stock, which is nice. Guess I have my next shopping list.

Thanks.
Phillip
 
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