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new bathroom subflooring for an unusual build

I'm redoing an upstairs bathroom. The house was built in 1900, it is balloon construction with the upstairs floor being 3/4 tongue and grove oak flooring nailed directly to 2x12 joists running from the front to the back of the house. The upstairs interior walls are built on top of the flooring. At some point someone covered part of the floor in the bathroom with glue and vinyl tile. To make matters worse the wall used as the wet wall is only 2 inches thick, original 2x4s flipped the wrong way some of which have a 3 inch gap cut in them to allow the old 2 inch galvanized vent pipe to pass threw them in order to connect into the vertical vent pipe that ran into the attic and threw the roof.

1st question do I cut the old floor boards out back to the existing walls to lay in a new subfloor (23/32 pressure treated tongue and grove plywood)? Or do I go over the existing floor with something?

2nd question the wet wall needs to be located where it is to avoid having to move the main soil stack, and other drains already connected to it. Can I fur it out another 2 inches using pressure treated 2x4? or, Do I remove the wall and put a new wall up (using pressure treated 2x4)?

A. Spruce
Re: new bathroom subflooring for an unusual build

There is no need to use pressure treated anything in this location, as PT materials are only necessary when in contact with concrete slabs and foundations.

There is no need to pull out the original T&G subfloor unless there is rot damage, simply remove the vinyl tile if it is loose, if it is sound, go over the top of it with your new flooring. If there is damage to the original subfloor, you only need replace the portion that is damaged. I would use plywood, since it's the easiest to use for covering larger areas. At the transition between the old and the repair, place a 2x4 or 2x6 joist to support the now raw edges.

Yes, you can fur out the wet wall with standard lumber, not PT, to be more accommodating to your needs, the only caution here is that you do not diminish the bathroom space, meaning a standard tub is 30"x60", don't encroach on that space or your tub isn't going to fit. Premade shower pans will have the same problem. If you do custom tile work, then the interior space doesn't matter because the custom work can accommodate whatever you have.

Re: new bathroom subflooring for an unusual build

The first thing to check is to see if the floor can handle tile. To figure that out, you need to know the deflection of the floor joists. You can find that out by using the handy dandy deflecto-meter on the John Bridge Tile Forum. There you can start a thread for your project, post pictures, read the extensive library, and get answers specific to your house.

Tell them wer sent you.

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