Replacing end of PVC waste pipe and toilet flange - DIY?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by jsr1017, Feb 5, 2014.

  1. jsr1017

    jsr1017 New Member

    Messages:
    5
    Location:
    Minnesota
    Here's the story: I've pretty much gutted the shower/toilet side of my master bathroom - it's a weird layout, with toilet/shower in an enclosed room on one side of a hallway and the vanity on the other. After I took up the ugly old tile the previous owners had laid I discovered that at some point in the past they had also removed and replaced a big chunk of the subfloor. That actually worked out nicely for me, because the replacement piece was just screwed down to the joists so I could easily remove it and get to the wiring to move the light switch to the other side of the door, since I'm also replacing the old swinging door with a pocket door.

    I'm a relatively new DIY'er, I'm pretty handy but this is the first time I've tackled such a big project so I'm learning as I go. I have successfully laid marble tile and sheetrocked the walls on the vanity side of the bathroom, and I got the framing for the pocket door track nice and level and plumb. :) But plumbing makes me nervous ... I had a pro come in and convert the single supply and drain for the old vanity to a double lines.

    So finally, my question: what to do about the old toilet flange? It's an outside 3" flange, installed with PVC cement, so I can't just cut it off easily. I've also noticed that it is installed 14" O.C. from the studs ... which seems wrong in any case, shouldn't it be 14-1/2" from the studs to account for the Hardibacker that will go up as the tile substrate on the wall? And even if that was okay, from my research it seems like there are far fewer 14" rough-in toilets to choose from than standard 12" ones.

    What I think the Right Thing (tm) to do is: cut the old waste pipe right at the coupler, at about 7-11/16" in the first photo below. Then reproduce, more-or-less, the collection of bends that are on there now, but place the center of the final closet bend at 12-1/2" from the studs, and do *not install the closet flange yet. Install some blocking around the closet bend so the screws that will eventually hold down the flange have some meat to grab on to, the replace the subfloor section - I'm going to use 1/2" ply with 1/2" Hardibacker on top, that will match the height of the tile in the hallway. Don't install the toilet flange until the tile is laid and I'm ready to actually install the toilet.

    That sound right?

    It seems to me that replacing the PVC is something I should be able to DIY - I've worked with PVC cement and primer before so I'm familiar with the process. I know to dry-fit all the pieces and make alignment marks so I can get everything in place after applying the cement. Are there any gotchas here I need to worry about?

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  2. jim mills

    jim mills New Member

    Messages:
    141
    Location:
    nebraska
    If you can get that flange moved over with that duct in the way, then go for it. Your plan is right on the money. Now using 1/2" ply for the subfloor won't fly, but that's another topic for another forum.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,051
    Location:
    New England
    Dry fitting pvc is dangerous! Especially with bigger pipe, and that the sockets are tapered, you generally cannot get the pipe all the way seated until it is softened up (literally melts) when the cement is applied...take careful measurements, not dry-fit if you want it to end where you really want.

    The toilet rough-in is from the finished wall, and if you can, you'd really prefer a 12" rough-in unless you're reusing an older toilet that's 14". In dry areas, you can tile directly to 1/2" cbu on the wall, or just standard 1/2" drywall...as long as it doesn't get wet, either works outside of the shower - your choice.

    Note that on most toilets, there's a bit more room behind the lower part than there is at the tank area, so things like baseboard, unless exceedingly thick, normally do not come into play with the rough-in. While it varies with brand and model, somewhere around 3/4" clearance behind the tank is fairly normal when the rough-in is exact. You may want to choose your toilet first. If it were only drywall going up there with paint, you'd want the center to be 12-1/2" from the studs. Throw in whatever sized tile, especially if it is going all the way up or at least above the toilet top, into that.

    Some toilet flanges are available without a socket (or stop), so as long as you leave enough room around it, you could leave the pipe high and install the new flange, then cut off the excess that sticks out through it when your finished floor is in. You really want to select a flange that has a metal (SS) ring, the all plastic ones tend to warp and you can break out the slots for the bolts if the toilet gets bumped hard.
  4. jsr1017

    jsr1017 New Member

    Messages:
    5
    Location:
    Minnesota
    Thanks for the reply. Yeah, that duct is a PITA, but I'm moving the flange along it, towards the wall where the tape measure starts in the photo and not further across it so it's no different than it is now. Depending on exactly where I lay out the shower curb, I might even have a few inches leeway to move the flange away from the duct, that would be nice.

    Re. the 1/2" ply subfloor ... I know it's not "right". But there will be 1/2" hardibacker laminated on top of it with thinset and a ton of screws. To go to 3/4" ply and 1/4" Hardibacker would cause tons of other problems in matching the remains of the existing subfloor, since I'm only replacing a patch that the previous owner cut out of the middle of the room. :(
  5. jsr1017

    jsr1017 New Member

    Messages:
    5
    Location:
    Minnesota
    Thanks for the tip about dry-fitting, I wouldn't have thought of that. Measuring a set of bends like that in 3-d space seems like it could be error-prone, is there a special technique that helps get it precisely right?
  6. jim mills

    jim mills New Member

    Messages:
    141
    Location:
    nebraska
    DOH! Was getting late when I read your OP. Moving it to the left is a piece of cake. You can pretty much duplicate the existing bend, then cut the horizontal line up next to the hub on the lowest elbow and be about right where you need to be. Might consider a cable cutter to make that cut. They are cheap, and work pretty well.
    +1 on the SS flange
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,051
    Location:
    New England
    From a structural viewpoint, you should not count on cbu for any floor strength. 1/2" ply is not, nor ever was considered a suitable subfloor for tile (or anything, really). The TCNA calls for a minimum of 5/8" ply (or osb) at typical joist spacings of 16" OC. Then, throw in the fact that it is a patch, and you have potentially more problems. Ideally, any patch would attach to three joists (i.e., one in the middle). That way, it's not relying on it just hanging on 1/2 of a joist connection at each end. If you can add some blocking in there, the patch can be smaller and still solid.
  8. jsr1017

    jsr1017 New Member

    Messages:
    5
    Location:
    Minnesota
    The "patch" is about 5-1/2' x 6-1/2' and is actually almost the entire floor in that room. The previous owner cut out the old subfloor at roughly (VERY roughly) 2" around the perimeter of the room, I assume that was the width of his circular saw guard plate and so he couldn't/didn't get any closer to the bottom plates. I'll take another look at what it would take to go to 5/8" or 3/4" ply.

    I did get the old waste pipe cut last night, the cable cutter worked great! Cost me about $6.50 at Home Depot. Tonight I'll go get the parts to replicate those bends.
  9. jsr1017

    jsr1017 New Member

    Messages:
    5
    Location:
    Minnesota
    I finally got the new waste pipe in tonight, after a few false starts and a lot of head scratching. I ended up using a long-sweep 90 elbow, and two street 45's. The only way I could get the height even close, with having to work around that duct, was to end up with the fitting on the last street 45 on top, ready to accept a 3" spigot flange with an SS ring from Sioux Chief. But before I start putting the subfloor and CBU back down I'm hoping you guys can confirm that I should be okay with the following two things:

    1. As best I could tell without actually gluing one together, the spigot fit flange is not made for the hub that is receiving it to be flush with the finish floor, my estimate was that the bottom surface of the flange will sit maybe 3/16" to 1/4" above the lip of the hub. So I stacked a piece of subfloor, CBU and tile (without thinset) and aimed for the lip of the hub to sit about 1/8th below the top edge of the tile. I'm guessing the thinset layers will add another 1/16" or so, so I should be pretty close. Sound good?

    2. In order to get to that height, I cut about 1/4" off of the pipe end on the first street 45, before gluing it into the upper hub of the 90 elbow. It was still a decently snug fit before gluing, although not nearly as tight as before I cut it. Is this okay? This is the joint in the center of the first photo.

    I did manage to nail the placement of the hub, 12-3/4" from the rear wall and 16" from the side. :)

    For a noob, this was a damn stressful part of the project since once the finish floor is laid there's no way to fix it it if it's wrong, without ripping up the floor or going up through the basement ceiling below. :(

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