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I am doing a complete gut remodel of my bathroom in a 1962 construction home. The subfloor is 1-5/8" x 7" tongue and groove set on 4 x 6 girders that are spaced 48" OC.

A leaky toilet completely destroyed a section of the subfloor, and caused rot to eat through at least 50% of a 4 x 6 girder. There is no floor sagging, but I imagine the beam needs replacement.

I can't find a match for the T&G planks, and the height makes substituting it with plywood a no go. Since the girders are 48" apart, I can't do plywood anyways, unless I add a bunch of joists.

No idea how to address this.

Removed toilet to reveal rotten subfloor:

enter image description here

Rotten girder:

enter image description here

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    Go to a woodyard - they will make planks for you - one advantage compared to these big "supermarkets" that only want to sell you what they think you should have... – Solar Mike Jun 15 '20 at 5:16
  • How long is that joist? just replace it. It looks like it has been supported in the past. – Solar Mike Jun 15 '20 at 5:19
  • It looks like it's 10' long, so I don't think I could get a single beam under the house. Since girders are main support structure and so far apart, would replacing it require blocking / jacking up the house? If placing new planks, how would I attach them, since the spans between girders so far, and no joists. – coreytrv Jun 15 '20 at 5:58
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You may need to make a hole in the subfloor wall of your house to pass the new beam under the floor, there may be a conveniently placed vent grid.

replacment planks should probably span between girders.

Trim the rotted planks back flush with the side of the good girders then fit a ledger board along the girder to support the ends of the new boards

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  • Not sure I understand what you mean by hole in subfloor wall / vent grid. Regarding spanning of planks to girders- the nearest one is adjacent the foundation wall, the other is about 8-10' away in another room, and has walls resting on it. How do I replace with such a span. – coreytrv Jun 15 '20 at 14:06
  • @coreytrv Somewhere above grade, but below the inside floor level, make an opening in the foundation wall (or take advantage of an existing vent opening). Using this opening, slide the new 10' beam in to replace the one that's rotted out. You can also use this opening to remove the rotten beam. You may have to make an "above grade" section of foundation by lowering the grade temporarily so you can get access to the foundation wall. – FreeMan Jul 15 '20 at 15:58

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