Sub Floor Support

[Jadnashua]

How close is the drain pipe to the bottom of the subflooring?

If you have enough room, I'd glue and screw a cleat of plywood as wide as I could fit to the bottom, then glue and screw the replacement ply onto it. You want to make it as wide as possible so you get the load spread, and a liquid wood glue would be better than something you caulk out as you can get a full spread...construction adhesive works great on say the top of a joist, but doesn't spread like a liquid glue does when you try to get full coverage over a wider surface.

Ideally, when patching, you want the patch to span two joist bays (three lines of fasteners) so that it's not hanging off of the fasteners at the end. Putting a cleat underneath helps make it stiffer.

 

[wwhitney]

No access from below? 10" away, so the I-joists are more than 16" o.c.?

Did you check farther down the joist bay to see if there's another crosswise block? If there is one nearby (say < 6' from the block on the right), and you have height above the pipe for an upright 2x4 (not flatwise), you could run an upright 2x4 between blocks, parallel to the joist. That would support the long seam along the wall.

Failing that, a minimal option would be to do a plywood splice on two sides (one long, one short) and then you have bearing on the other two sides. With glue and screws, it probably would be strong enough, not sure.

I would think even at 10" away, you'd be able to maneuver the flatwise 2x4s into place and put the toe screws in. Admittedly it would be a stretch getting your driver and your hand into the joist bay, but I think doable. Maybe put one at the left side (could only get one screw in to the far I-joist top flange, but that's better than zero), and one in the middle. Then two plywood splice plates in between.

Cheers, Wayne

 

[Sponsor]

 

[Reach4]

Yes, but I don't know why you would need an L shape. Ah.. I see it now... I think using two pieces will be easier. How about pieces of 2x4 rather than plywood? But plywood should work too, and I guess you will have spare plywood. . So whatever you attach will have its top even with the tops of the other wood that you are laying your new plywood piece onto.

If you have to notch out part of that 2x 3 to clear the hub of that wye, that's fine.

 

[Jason Kay]

The final product. Was able to get 2X 4 to span across joists with 1 toe screw in each far end of the 2x4. Should be good now. Thanks everybody

 

[Reach4]

I would like to see screws through the plywood down into the 2x4, with glue on the mating surfaces.

 

[wwhitney]

I would like to see screws through the plywood down into the 2x4

The picture shows screws along the long edge of the opening, their heads are just well color matched with the grey plywood.

Cheers, Wayne

 

[Reach4]

The picture shows screws along the long edge of the opening, their heads are just well color matched with the grey plywood.

Cool. I saw "1 toe screw" and was afraid that was the extent.