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Thread: Moving a toilet waste line 5.5 feet... Possible?

  1. #1
    DIY Junior Member rpdwyer's Avatar
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    Default Moving a toilet waste line 5.5 feet... Possible?

    Hello all.

    Just joined this forum looking for some advice.

    I have a master bath that was rough plumbed 10 years ago. We are only starting to convert it to a finished master bath (until now, it's just been used as storage). The problem is, the location of the 3" waste pipe is about 5'6" from where it needs to be. Unfortunately, my floor joists run perpendicular to the direction it needs to move so I would have to cut holes through four 10" floor joists to route the pipe to the new location.

    First question is, can I get enough slope for a 3" pipe moving it 5'6" to drain correctly? (it currently comes up through a wall and then moves about 1'6" horizontally to the point where the flange comes through the floor)

    Second question is, given that the joists are only 10", can I even punch a 3" hole through 4 of them without weakening them too severely? If it can be done, how do you shore up the joists..... laminate them with glued plywood?

    Thanks for any info.

    --Rick
    Last edited by rpdwyer; 11-26-2012 at 05:26 PM. Reason: typo's

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    The grade would be 1/4" per foot
    A 2x10 joist is 9.25" deep.
    At least 2" must remain on the bottom and on the top of the floor joist.

  3. #3
    In the Trades Gary Swart's Avatar
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    I would sister 2x2's at the top of both sides of each joist you drill just to provide extra support and strength to the joist. May be a bit more than really needed, but cheap and easy to do.

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    DIY Junior Member rpdwyer's Avatar
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    Thanks Terry.

    OK, so if I start my penetration on the first joist right at the 2" mark (from the bottom of the joist)... when I punch through my fourth joist next to the new toilet location, with a 1/4" inch slope per foot, I have increased my height by 1.5" to put me 3.75" below the top of edge of the last joist. However, that also means my (nearly) horizontal pipe is just 4.5" below the finished grade. Does that 4.5" give me enough room to put a 90 degree toilet flange onto the horizontal pipe?... or do I require more clearance than that?

    On the diagram below, the opaque red lines are the joists. The red paint brush stroke is the current pipe location and the green paint brush is the proposed run and location.

    Thanks again.


    --Rick
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    Last edited by rpdwyer; 11-26-2012 at 05:59 PM.

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    DIY Junior Member rpdwyer's Avatar
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    Quote Originally Posted by Gary Swart View Post
    I would sister 2x2's at the top of both sides of each joist you drill just to provide extra support and strength to the joist. May be a bit more than really needed, but cheap and easy to do.
    Gary, thanks.

    Great idea. Glue and screw 2x2's. I've seen plywood used as well, glued and screw before the holes are punched to add extra support. Not sure which would be stronger, but I'm not afraid of overkill in this situation.

    --Rick

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    Moderator & Master Plumber hj's Avatar
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    How much "strength" do you really think a 2x2, (actually 1.5 x 1.5), would add to it? Your "saving grace" is that the holes will be close to a supporting wall underneath them, rather than in the center of the span. That means that the joists would almost have to "shear" to fail, rather than sag and bend in the middle.], and wood does not shear easily.
    Licensed residential and commercial plumber

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Quote Originally Posted by hj View Post
    How much "strength" do you really think a 2x2, (actually 1.5 x 1.5), would add to it? Your "saving grace" is that the holes will be close to a supporting wall underneath them, rather than in the center of the span. That means that the joists would almost have to "shear" to fail, rather than sag and bend in the middle.], and wood does not shear easily.
    My thoughts exactly. I would still beef up the joist, but it's going to be tough to glue and screw a 2x2. I'd glue and screw some 3/4 plywood to both sides of the joists and then bore as small a hole as necessary through the ply-joist-ply "sammich." It's better to overkill, but make it count.

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    Forum Admin, Expert Plumber Terry's Avatar
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    If you intend to add something to the floor joist, it would be better to use plywood.
    That, or drop below the floor joist.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Make sure to maintain the downward slope of the drainage system pipe you add. that means that the new end will be about 3/8" higher than the existing end. Elbows take up space to bend it up towards the floor, and even that little extra can be a challenge in tight spaces.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10
    DIY Junior Member rpdwyer's Avatar
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    OK, so plywood glued and screwed to each joist... not a problem. However, as per my previous post, my concern is the finished position of the horizontal pipe in it's new location. It will likely be about 4" to 4.5" below the finished floor grade before I put the 90 degree bend on it and the toilet flange. Is that enough room for a 90 and flange and not have the flange sticking up above the finished floor grade?

    Thanks,
    --Rick

  11. #11
    Forum Admin, Expert Plumber Terry's Avatar
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    You will need to buy the fittings and find out. I normally carry all kinds of flanges and bends in the van.
    The bend that uses the least amount of space, is the 4x3 spigot closet bend with 4" hub flange. You can slide the closet flange as far down as you need and trim the excess from the top of the bend.

  12. #12
    DIY Junior Member rpdwyer's Avatar
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    OK, thanks Terry and to all those who responded.

    --Rick

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