Shower Install -- How Downsize Existing Drain Hole Siize

Discussion in 'Shower & bathtub Forum & Blog' started by unionmaid, Jan 19, 2010.

  1. unionmaid

    unionmaid New Member

    Messages:
    2
    Location:
    Johnstown, OH
    We're installing a cement shower pan in our upstairs bathroom.

    The existing drain hole in the sub floor is too big -- 7.5" diameter.

    Our abs Oatey drain requires only a 4.5" hole.

    The sub floor is made of 3/4 plywood over joists.

    Any recommendations?

    TIA
  2. VolsMan

    VolsMan New Member

    Messages:
    2
    Location:
    West TN
    Hello,

    One way I would consider is to set the blade depth of circular saw to cut 3\4", remove the appropriate nails in the sub floor and cut a 16" square of the subfloor(center of one floor joist to center of other floor joist) that incorparates the 7.5" diameter existing hole. Properly replace with new piece of 3\4" and re-cut the hole the desired size.

    Bubba
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,006
    Location:
    New England
    That's a reasonable approach, but I'd also consider putting in some blocking on the cross joist ends of the patch otherwise, it will not be as sturdy, which is highly desireable under a shower pan. Check out www.johnbridge.com for help on tiling. For maximum strength, a patch should bridge two joist bays and anchor to three joists. If you put blocking in, it's almost as strong.
  4. unionmaid

    unionmaid New Member

    Messages:
    2
    Location:
    Johnstown, OH
    Thank you Jim and Bubba. We have been reading a lot on the johnbridge site and that has been helpful. We got the shower floor done by laying down another sheet of 3/4" plywood. Mortar shower pan is next.
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