Subfloor cutout too large?

[Danpe]

We are in the process of remodeling the bathroom. Installing tile floor, new vanity and a new Toto Drake toilet. This is what i found supporting the old toilet. The old flooring was a "pergo" laminate wood flooring product (prior owners installed). I plan on installing the cast iron flange with the compression ring system. As you can see there is very little real estate to support the flange even after I lay a 1/4 ply, uncoupling membrane, and tile. I also need to take care of the other wood damage. Thought I would post this picture for any suggestions.

 

[Gary Swart]

I'm not a pro and you may get different advice from others, but this is what I'd do. I'd cut the existing floor to the joists on each side. Then I'd sister pieces of 2x4s to the joists and use them as supports for a piece of 3/4" plywood cut a bit larger than the space. I'd then cut the hole for the flange allowance for final trimming of the plywood. Then I'd measure from the edges of that hole to find where to cut the plywood edges to fit the hole.

 

[Sponsor]

 

[Danpe]

Thank you for the reply. Sounds like the proper approach. This subfloor is rough cut tongue and groove, over a 1.5 inches thick, and spans about 5' between joists (4x6's). Lots of plumbing and ductwork in the way. Sounds like I need to crawl under the house to take care of this one. Thanks again Gary.

 

[Gary Swart]

WOW! 5' between joist is a huge stretch. Likely have to modify my idea as I was assuming (dumb thing to do) a "normal" spacing and a 3/4" sub floor. You will want to be sure the sub floor is well supported.

 

[JohnfrWhipple]

Thank you for the reply. Sounds like the proper approach. This subfloor is rough cut tongue and groove, over a 1.5 inches thick, and spans about 5' between joists (4x6's). Lots of plumbing and ductwork in the way. Sounds like I need to crawl under the house to take care of this one. Thanks again Gary.

5' spans? Really.... And you plan to top that with 1/4" plywood and an uncoupling system?

Good luck with that. I'll warn you that there was a reason there was not tile in that room before. That floor is no where near close enough to being ready for tile.

The shiplap boards are also not supporting each other.

If you plan on tile - start doing your homework.

 

[Danpe]

Thought I would follow up with a picture of the repaired cut out after spending much time below my house bolstering the floor (placing concrete, footings, and supporting members, and ply on the under side). My guess of a 5 foot span turned out to actually be 4 foot. The 1/4" placed over the reinforced floor and the final result is quite solid. Total thickness of wood is 2 and 3/4 inches.