Moving bathtub drain

Discussion in 'Shower & Bathtub Forum & Blog' started by Tee Jay, Sep 21, 2021.

  1. Tee Jay

    Tee Jay New Member

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    Sep 21, 2021
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    Edmonton
    Hello,

    I am in the process of renovating my master ensuite and I am struggling to figure out how to move the bathtub drain.

    I removed a large corner jacuzzi and I am hoping to reuse the takeoff as it is really tight where the new drain needs to go. Is it possible to cut the current takeoff, and then loop it back in to where the drain needs to be? Plan would be to cut the current takeoff arm from the wye add a 45 to run a pipe along the 3" vent stack, and then a 90 degree back into the middle of the cavity to squeeze a trap in between the vent and the toilet drain.

    I don't think I have room to cut out the bathtub current wye, and add a new one with the take off on the other side. There is also no give in the pipe to be able to move it around to slide one in. I would need to redo it all back from the main stack which I am trying to avoid if possible.

    I have attached a couple pictures for clarity taken from below as I have opened up the room underneath for a different renovation.
     

    Attached Files:

  2. wwhitney

    wwhitney Well-Known Member

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    Location:
    Berkeley, CA
    That's not an allowed configuration.

    I'm a bit unclear on what is upstream in the area marked "vent stack". But it appears the old tub drain is getting wet vented at the 3x3x2 (or 1-1/2?) wye where it connects to the 3" drain. [Which means that upstream on that 3" line should be a dry vented bathroom fixture like a lavatory.]

    The tub trap arm can only fall one pipe diameter from the trap elbow outlet to the vent connection (so 1-1/2" or 2", depending on what size trap you use, either works for a tub). That means you can't use the 3x3x2 (or 1-1/2") wye for wet venting the tub trap arm, if it crosses over above that 3" horizontal drain , it would end up falling too far before being vented..

    The only way you could use the routing in your picture would be to provide a separate dry vent takeoff for the tub trap arm above the 3" drain, before the tub fixture drain turns down to connect to the existing horizontal wye. And the dry vent has to rise vertically (up to 45 degrees off plumb) until above the flood rim level of the tub. Could be possible if there's a wall right there, but it looks very tight.

    Cheers, Wayne
     
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  4. Tee Jay

    Tee Jay New Member

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    Hmm, thanks Wayne for the reply.

    I added a couple other pictures to maybe give it more clarity. The one picture gives an expanded view of the "vent stack". The drain stack comes up from the basement and then the 3" pipe on the right of the wye goes to the toilet flange, and the 3" side on the left goes to the old tub drain (connected via the 1 1/2" wye) before heading up and out the roof. So upstream on the pipe from the bathtub is dry vent. Well at least that is my interpretation of it.

    I included the second picture of the upstairs wall where that vent stack goes up and out the roof. The 1 1/2" pipe that connects in is the vent from the bathroom in the basement and the laundry room that is below the master bathroom.

    I certainly don't think there is space to run a separate vent line from the tub drain at 45 above the top of the tub in the space. As you can see, the wall that it runs into as is already has a lot of runs in the space.

    The sinks are on a different line as is the shower so they aren't considered in what I was trying to do (that is, they use a different 3" line going to the basement.
     

    Attached Files:

  5. wwhitney

    wwhitney Well-Known Member

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    If the 3" line on the left, upstream of the wye where the bathtub currently comes in, is completely dry with no fixture draining through, then that would not be an allowed vent under the US codes. Perhaps your Canadian code would allow it.

    How is your WC vented?

    That elbow on the top of the 3rd photo in the thread, one possibility is to put a san-tee right above the elbow. The side entry would receive the tub trap arm. That would work if it would fit vertically, and if the tub trap arm would be close enough so that it falls only one pipe diameter and meets whatever length limit is in your code.

    Cheers, Wayne
     
  6. Tee Jay

    Tee Jay New Member

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    Edmonton
    House was built in 1987, so not sure if things were different then but that is certainly all original. There is no fixture draining through the 3" line on the left upstream of the wye.

    The WC has no other vent other than what is in the 3rd picture on the thread. My assumption was that the vent for the tub and the toilet were all the 3" line upstream of the wye on the left after the tub.

    The elbow on the top of the 3rd photo is the pipe you see in the 4th photo which goes out the roof. If I understand what you are saying correctly, that would be above the floor level and unable to be used for the tub drain as it would be too high vertically

    Plumbers are a hot commodity out here otherwise I certainly would leave this to the experts. I have had 4 come out to look at it, never heard from again. The others who I called don't even call back. At least with the resin shortage, the tub is 10 weeks out so there is time to figure it out.
     
  7. Tee Jay

    Tee Jay New Member

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    So I have been looking at this for the past two weeks and I can't figure out how to make this work.

    Wayne, I thought about putting the san-tee right above the elbow as you suggested but that would mean that the side entry for the tub would be above the floor that the tub is sitting in (4th picture in the thread). The elbow basically is at the floor level already so anything above it won't work.

    Is the issue with the 3" pipe that goes out the ceiling the fact that it runs horizontally first before going vertically to use that as a vent for the tub?
     
  8. wwhitney

    wwhitney Well-Known Member

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    One possibility to consider is replacing the LT 90 with a 45 - santee - 45 with street connections. The san-tee side inlet has to point perpendicular to the plane of the 90 bend, though, which may not work for you, as the WC drain is so close.

    Also, the 3" horizontal pipe needs to have a fall of 1/4" per foot downstream (unless your code allows 1/8" / foot on 3", one of the US codes does). So you could check the rate of fall on the horizontal vent from the 3" wye where the WC drain comes in upstream to the elbow where it turns up. If that's falling (downstream) at faster than 1/4" per foot, you can lower the LT 90 or its replacement, which could help you. If the combined drain falls from the 3" wye to where it turns down into the basement wall at faster than 1/4" per foot, then you could also consider lowering the 3" wye to gain further vertical room. That could be tricky without modifying the 3" WC drain but might be possible.

    Perhaps the Canadian code differs, but a pipe that is a dry vent (vent only, no drainage) needs to come off the drain it is venting vertically, not horizontally. A horizontal vent takeoff could be subject to some backwash from the drain, and solids could accumulate and impair the vent (or so I understand the reason for the rule). If you only have space for a horizontal vent takeoff, then that is allowed for a wet vent, e.g. if you could move the vanity drain to drain into the tub vent pipe above the floor. That way the drainage from the lavatory should prevent accumulation of solids at the tub drain/vent connection. Wet venting has its own restrictions, but would be fine here for another bathroom fixture.

    Cheers, Wayne
     
  9. Tee Jay

    Tee Jay New Member

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    I went and looked at that connection again, it actually isn't a 90, it is 2 45's butted together with a short piece of pipe. I mocked it up with 1 1/2" as that is what I have sitting around. Is this what you were thinking? If so I think it would be too tight as from the edge of the 3" pipe, I only have 10.5" to the center of the drain. It also needs to end up in between the 2 3" pipes for it to be lined up correctly. I would basically have to make a loop back to the location.
    20211004_143535_resized.jpg

    The pipe does have the correct fall right now, it is already quite low so I don't think I can lower it and maintain the slope.


    Oh that makes sense, never though about it before. The vanity is on the other side of the bathroom and is routed with the shower to a different stack to the basement.

    The only other way I can think of is to connect to the 2" shower drain pipe on the other side of the room. The only think with this is that I would need to build a bulkhead below the joists for the pipe to the tub.
    Upstairs Ensuite - New.jpg
     
  10. wwhitney

    wwhitney Well-Known Member

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    Given that, are you sure that using a street LT 90 coming out of a 3x3x1-1/2" san-tee (or 2" if you want to use a 2" bathtub trap and have enough space) puts the 1-1/2" drain too high for your bath tub? How much too high?

    I don't think the following would fit, and it would require some carpentry, but the LT90/san-tee above could in theory be rolled 45 degrees towards the 3" WC drain. If it doesn't hit the WC drain, then that would lower the san-tee inlet. Then a (street) 3" 45 on top would get your vent plumb again, above the floor. There's a stud in the way that would have to be cut back or otherwise dealt with, assuming that's not a load bearing wall. Then above the floor a couple more 45s to jog back to line up with the current vent.

    Yeah, that was my guess but I figure it was still worth mentioning.

    Obviously you could do that with the resultant tradeoffs, but it would be nice to convert the horizontal dry vent into a proper wet vent. I'll think about it some more.

    Cheers, Wayne
     
  11. Tee Jay

    Tee Jay New Member

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    I think the blue store by me has a long turn 90 street as my local orange box only has a short radius. I'm assuming the SR wouldn't be allowed as this would be a waste stack. Is that correct or is that allowed with 3" pipe?

    I will try to pick one up today and see if I can make the measurements work. For your second thought, I will also see how much I can roll it as that would certainly help but maybe with removing the 2 45's I could make it work vertically instead of having to roll it. The wall above isn't load bearing so I can hack it up a bit. I would need to move the 1 1/2" vent that ties into the 3" within that wall as it is in the way if I go this route.

    Appreciate the response and your thoughts, I'll see what I can get figured out for sizes tonight and report back.
     
  12. wwhitney

    wwhitney Well-Known Member

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    OK, I got my left/right mixed up when going from the below floor picture to the above floor picture, so you'd be rolling it towards the duct, not towards the stud. I'm guessing then that the duct would prevent you from rolling the LT 90 + santee 45 degrees, but you might be able to roll it 22.5. That wouldn't give you much elevation change, but if you're otherwise close it might make the difference.

    As to using a quarter bend instead of a LT90, in plastic the difference is only 1" of elevation. The codes I'm familiar with would require a LT90, but you'd have to check your code.

    One other possibility is doing some of the work in 2" instead of 3". Because for a WC vent, and for a bathtub, 2" would be plenty. So going upstream, you could change to 2" on the horizontal, do the above fittings in 2", and then reconnect to the 3" vent above. There's two possible issues with that: one is the upsizing of the vent; that's commonly done near the thermal envelope in cold climates, I'm not sure if it's legitimate to do it lower down. The other is whether your code requires you to have an unrestricted 3" vent in that location. One US code (IPC) is very flexible on vent sizes and it would be no problem; the other US code would allow 2" there, but would require that there are other vents whose area add up to the equivalent of 3" (or 4" if you have more than (3) WCs in the house).

    Cheers, Wayne
     
  13. Tee Jay

    Tee Jay New Member

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    I might have to check if I can downsize to the 2" as that would gain me some space. I'll check with the inspection office on that. I checked my code and certainly need the LT90 instead of the 1/4 turn. I picked one up but from the bottom of the pipe to the top of the santee take off for the tub, it would put the santee about 1 1/4" above the joist. The trap would have to run uphill to get to it so that isn't going to work.

    If I roll it 45 towards the duct, I have the clearance for the santee under the floor but then it is above the WC pipe so might not be room to get the trap in. I'll have to see if I can cut an access hole from the top to see if that works in the space.

    Thanks again for your input, barring cutting holes in the subfloor, I'm back to the drawing board unless I can get household agreement for a bulkhead.
     
  14. wwhitney

    wwhitney Well-Known Member

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    A not great option is to put the tub on a small platform. They also make above-floor-drain tubs where the platform is effectively built in.

    Also, just want to double check you used a street connection on the LT90 and san-tee. If you used two hubs touching, that's an unnecessary 1.5" of extra height for 3" fittings.

    Here's one more possibility for you, you have to check your plumbing code. One of the US codes (IPC) would allow this; one (UPC) would not. The idea is that you start by removing all of the 3" parallel pipe runs. Then the 3" WC drain gets rerouted to pass under the current 3" vent location, and the vent takeoff for the WC is an upright 3" combo (actually the IPC would allow a san-tee on its back, which I only suggest when the combo would be really hard to fit). Now the tub drain goes in with the trap outlet at about the same centerline elevation as the rerouted WC line and the trap arm runs briefly parallel to it. Then the trap arm joins the 3" WC drain with a 45 bend and a horizontal 3x3x1-1/2 (or 2) wye. The WC is horizontally wet venting the tub.

    I'm assuming in the above that the WC is on the other side of that wall you've pictured, and so at least 18" farther up the joist bay, with enough room for you to move the WC drain layout. E.g. rotate the closet bend 45 degrees, and then hit a 45 degree elbow to end up in line with what is currently the 3" horizontal dry vent.

    Cheers, Wayne
     
  15. wwhitney

    wwhitney Well-Known Member

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    P.S. A variant on the last idea, if your code doesn't allow a WC to wet vent the tub, is to separately dry vent the tub. That would be possible if down the joist bay the tub trap arm would pass under a wall within the allowable length limit and you could run a dry vent up into that wall. Possibly reconnecting the tub dry vent with the 3" vent in the ceiling above.

    Cheers, Wayne
     
  16. Tee Jay

    Tee Jay New Member

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    Hi Wayne, yes I used the street LT90. To get the slope on the 3" pipe back to the stack, I have about 7. 3/4" to work with from the bottom of the pipe to the floor about. The measurement from the bottom of the hub on the LT90 to the top of the santee was just shy of 9". I believe that I read that a WC can wet vent the tub, so I will go check into that some more.

    I'll need to check the Canadian code to see if that is allowed, it certainly is an interesting option. You are correct that the WC is on the other side of that wall that the vent stack runs up right now so I can certainly see this working if the code will allow. I have an inspector coming out to see the laundry room pipe move I did so maybe I can inquire with them then.

    Thanks for all the ideas on this, I really appreciate it.
     
  17. Tee Jay

    Tee Jay New Member

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    Just wanted to make sure I understand what you are saying, I drew a crappy picture.

    This is what I think you were describing.

    Upstairs Ensuite - Oct 5.jpg

    I looked up in the Canadian code and I think this will be the problem on this method:
    2.5.2.1. Wet Venting (See Note A-2.5.2.1.)
    1) A soil-or-waste pipe is permitted to serve as a wet vent, provided
    d) the water closets are installed downstream of all other fixtures

    As the tub would be downstream of the WC, or am I interpreting this wrong.
     
  18. wwhitney

    wwhitney Well-Known Member

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    Your drawing does match my suggestion (where the 3x3x2 wye is horizontal), but assuming you found the correct version of your code, looks like you can't wet vent a tub with a WC. OK, here's my latest idea:

    The 3" pipe is as in your last drawing, which clears up the joist bay somewhat, no parallel 3" pipes. The tub gets a 1-1/2" trap and trap arm for minimum fitting sizes (if it works in 1-1/2", you can try it in 2" if you prefer a 2" trap). The trap arm go towards the wall above and hits a 1-1/2" san-tee under the wall. The top of the san-tee is a vent which rises up to 6" above the flood rims and then joins the 3" vent, along with that other vent that is there.

    Out the bottom of the san-tee comes a street 1-1/2" LT90 for the drain to run parallel to the 3" WC drain. This 1-1/2" drain has to end up with center line not below the 3" drain center-line, that's the crucial geometric constraint. Then the parallel drains join downstream. And if you have sufficient room left-right, you can reduce the vertical drop between trap arm and vented tub drain by rotating the san-tee 22.5 or 45 degrees around the side inlet, and using a 22.5 or 45 degree elbow at the top of the san-tee to get the vent plumb.

    For joining the parallel drains, you use a 1-1/2" 45 plus a 3x3x1-1/2" wye. That 45 plus wye can be either with a street 45 (which requires one exact distance between the two drains), or with a regular 45 (which can accommodate a different distance between them if the hubs touch, or any greater distance). If your parallel drains end up below the latter minimum distance but not at the street 45 distance, then you would need to jog the 1.5" drain with a pair of 22.5s to adjust the distance between the drains before joining them.

    Cheers, Wayne

    P.S. How/why is it that your layout puts the tub drain so far from the wall with the current 3" vent? If the tub and drain were up against the wall with the vent, venting the tub should be easy.
     
    Last edited: Oct 5, 2021
  19. Tee Jay

    Tee Jay New Member

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    I'm thinking I can make this one work. This is what I have drawn based on what you suggested. This seems so simple now, I can remove one of the 3" pipes, vent the toilet with the 3: stack connecting with a wye and then tie in a vented bathtub drain.
    Upstairs Ensuite - Oct 6.jpg


    It actually doesn't, I just don't know how to draw the pipes in perspective. This would be the view from above. The problem is the 3" pipe and height required. The easiest would be your suggestion yesterday to put a santee and LT street 90 at the bottom of the vent, I just don't have the height
    Tub Layout.png
     
  20. wwhitney

    wwhitney Well-Known Member

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    Yes, the existing layout with parallel 3" pipes is pretty weird, I guess it befuddled me for a while, trying to preserve that aspect. Your drawing matches what I described.

    As for the tub, since the drain is close to the wall above (I think either your yellow circle in the first couple photos is off, or I was thrown off by the perspective or had the wrong sense of scale), then you may have one more option for venting the tub drain. Often you can take the vent off the horizontal trap arm while keeping the drain horizontal, so you don't have the elevation loss of san-tee - LT90.

    It goes like this, for a standard tub with overflow and waste joining in a tee under the overflow: the trap u-bend points almost towards the wall, but turned enough for the next step not to cause self-interference. The trap elbow points directly away from the wall. Then a short pipe section to comply with the crown vent rule, and a vertical wye for the vent takeoff. The vent rises at a 45 degree angle back until it's into the wall. Often it may break the plane of the floor before it enters the wall and turns up with a 45, but usually there's some void space under the tub. So the constraint is whether it would hit the tub or can fit in the void space. Lowering the trap some can help avoid hitting the tub, at the cost of some elevation.

    The tub trap arrangement could vary from the above, e.g. tub trap directly towards the wall, elbow pointed away from the wall at a 45, then a (street) 45, then the vent wye. Whatever fits and gets your tub drain away from the obstructions.

    Cheers, Wayne
     
    Last edited: Oct 6, 2021
  21. Tee Jay

    Tee Jay New Member

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    I'm not getting on this how this saves me the san-tee LT90. I can certainly take the vent off the vertical wye. but the horizontal piece of the wye(the drain) would need to do a 180 to go back under the tub to the stack. Or am I missing something here?
     
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