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Thread: Subfloor cut-out for toilet flange and other questions.

  1. #1

    Default Subfloor cut-out for toilet flange and other questions.

    Thanks to the forum owner and administrator for a means to ask questions! This is great for a plumbing novice.

    This is more of a carpentry issue than plumbing but I'm sure many of you have already solved this.

    I've gutted my 1955 bathroom, including the tile floor and am replacing the subfloor (the subfloor was poured concrete and mud between and over the floor joists with tile on top). The toilet flange and waste line are all cast iron. My flange has two simple notches for the toilet bolts to hook onto, otherwise it's just a round disc. Hard for this untrained eye to tell just how it's attached. The flange appears to be in good shape.

    Question.. Can I cut a hole in the plywood subfloor, just wider than the flange and drop the plywood over the flange and waste line, or should I cut a seam down the centerline of where the toilet will sit and attempt to get a close fit to the flange collar/waste line? The distance from the flange collar to the outside of the flange is 5/8".

    Also, the waste line and flange were pretty well encased by the concrete subfloor. The wasteline just past the 90 elbow is supported by a single piece of steel strapping. Now that the concrete is gone, do I need to add any additional support to the flange and waste line? Got to believe this is pretty heavy pipe hanging out there!

    And, sorry to be so full of questions, but how high above final floor should the top of the toilet flange sit. I don't have the original instructions for my 20 year old American Standard toilet but instructions on-line for current toilets said about 5/8". I may end up being more like 3/8".. is this OK?

    Thanks for your help!

    Tom
    Beltsville, Md.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    A flange is designed to sit with its lip on top of the finished floor with no gap under it. The type you have, I don't know . All current flanges that I've seen have screw holes around it to anchor it to the subflooring and the slotted holes to insert the bolts to hold the toilet down. The whole portion above the floor is normally not much more than 3/16-1/4" above the finished floor. For many toilets, if it exceeds that, you can't get it to sit flush. My unprofessional opinion.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Master Plumber master plumber mark's Avatar
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    Talking floor install

    its just a little better when you put a seam in and try to get some
    wood under that toilet flange....
    it gives it some support if for no other reason.

    the finished flange on the floor can be flush and work fine.
    It can be a little lower and be ok too,

    just dont have the thing raised up much above the floor level or the
    toilet might "rock" when you re-set it.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default flange

    rather than try to cobble something together and try to make the old flange come out at the right height, hit the old flange with a hammer and chisel. It will crack and can then be removed. Do the subfloor properly with a hole large enough for the new flange to fit into it. Then tile and finish the floor. Call a plumber to come and lead/oakum caulk a new flange on. Cast iron systems do not need to have the flange anchored. They do not move when the toilet is connected to the flange.

  5. #5

    Default

    Jim, Mark, HJ,

    Thanks for your reccommendations! Sounds like I should do my best to get some support under the flange. I need to take a second, closer, look at where the floor will come up to. If it looks like I'm off a ways, I'll pop-off the flange per HJ's suggestion. Had one heck of a time breaking up my cast iron tub. Some places went easy, others required heavy impact. If I need to break off this cast flange, is there a "sweet spot" that I should start at to keep the impact low to the rest of the waste system?

    Thanks, again.

    Tom

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default flange

    The "sweet spots" are on both sides where the notchs are for the bolts. But there will be little stress on the rest of the system. The lead joint is a good buffer for that.

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