Leveling a bathroom floor...

[Triplegreen500]

So, I'm making progress on my rental renovation. Bathroom time. Question for builders/plumbers in the group (I'm "handy", but don't do this for a living or anything).

Toilet is about 16" from exterior wall. Cast iron pipe, not moving it. Floor drops 7/8" within 22" of the exterior wall, then levels out. It's the joists - they sag in the first 12-18" from the foundation, and level out. Old house (1952).

Subfloor is old-school diagonal 1x6 plank. Over that, is 3/4" thick hardwood. Over that is 1/8" linoleum tile. Over that, was 1/2" plywood and ceramic tile on top of that. I plan to use actual 1/2" backerboard, then ceramic tile. That should get me back to flange height so I can install a stable toilet.

Question is - the hardwood was rotten around the flange (73 years old...no surprise there). I have already cut it out as needed and exposed the subfloor. Subfloor is...decent enough. The sewer pipe comes up immediately next to a joist - as in, touching it. I could either:

1. replace the hardwood with some modern OSB for strength (on top of existing subfloor), stopping it where the floor starts to slope upwards (just behind the flange), and fill the remaining space with self-leveling filler

2. simply lay down some plastic (to cover gaps in the subfloor), and fill it all with self-leveler.

I would use the self-leveler only to the height of the existing/remaining hardwood and linoleum, so I could put my new layer of backerboard and tile on top and have it be a level surface for the toilet.

I'm not concerned about lots of weight bearing behind or next to the toilet - it's a 44-inch wide area and the toilet backs to an exterior wall. Nobody will be walking there. And again, there is a joist immediately next to the drain pipe - and I could frame in a second one on the other side of the pipe, by bridging joist-to-joist underneath, and then boxing that in next to the pipe. I think I'm good on support...I just need to level it properly. The levelers say they want to be used on concrete substrate...but again, it won't be a trafficked area as far as weight goes, so I think this won't be as much of a concern? I can shore up underneath the subfloor as needed, to help stabilize it without changing its height...but I can't see there being enough traffic in the area to ever crack the leveling sealant.

I won't be able to use physical fasteners through the backerboard into the leveling stuff...but a) the toilet will hold it down, b) there will be base moulding all around, at the bottoms of the walls, and c) I can use adhesive to help secure the backerboard to the leveling.

Crazy? Stupid? Or...just might work?

 

[RR Fan Dan]

Strap the drain pipe to the joist. Fill the gap wit 3/4 hardwood, not osb. This will also help

 

[Triplegreen500]

Any thoughts on the self leveler stuff? If I just lay ply on the subfloor, it'll be nearly an inch out over a 22 inch run.

I need to go from like 3/4 to 1/2 to 1/4 as it gets closer to the wall...should I fill those voids with the self leveler?

On top of either the voids, or the leveler, will be 3/4" of backer board plus the actual tile and adhesive....

 

[68-500]

Is the toilet flange level or does it follow the floor? I think id be tempted to fix all rotten flooring with layer of plywood then concrete board then finish the entire floor. If you try to level 1 portion and not the other you will have an unsightly bump or recession somewhere. Can you jack up the floor under the bathroom?

 

[Triplegreen500]

The bathroom itself is level (as is the flange). The floor drops that inch in the first 22 inches from the wall, and levels out. More like a flat floor that ramps up at the exterior wall end, if you will. It isn't the floor that's out of level, it's the joists - and no, I'm not going to shave the tops down to level them. That's too sketchy, even for me!

Floor joists are 2x12, from 1952. I ain't jacking anything up and getting a level result. Best I could do is put a post under joists in the basement to prevent further sag...but not gonna lift anything. It would just raise the "bent" part is all, it won't straighten out.

Level is...level. subfloor on the left, hardwood and linoleum on the right (you can see cut ends at top)

Old but solid cast iron pipe (yes, I'll install a repair flange)

Subfloor is passable...orange stripe is the joist. I think with 3/4 ply plus 1/2” cement board plus the tile it'll be plenty strong, I just need to level underneath the cement board.