Floor Prep - Bathroom Reno (please help)

I've seen so much conflicting information out there so hoping to consolidate everything here. I've got a few questions related to preparing my floor for an ongoing bathroom reno. Will try to keep concise and itemized to the few questions. If anyone were able to read just one of the questions and reply it would be appreciated. I decided on this approach rather than spamming the subreddit with multiple similar-ish posts Background: Ongoing demo. This is a second floor bath above a finished dining room (at all costs would rather avoid accessing from below). Existing subfloor is 3/4" OSB(? could be ply for all I honestly know?). Took off top layer of 1/8" ply that was definitely rotted (not shown). The existing sub shows some old signs of water damage around the tub and toilet area. Still quite firm. Am undecided between treating with some bleach to kill anything there and leave it as is, or rip out (more details later). My floor joists are a solid 2x10's at 14" on center spans (not standard 16 which is nice). Currently the floor has no deflection (play?) when walking or jumping on it. It does however have an issue with level. What I assume is one proud joist through the middle of the floor (or the house settling from framed walls) has caused a peak in the middle of the floor with just a hair over a 1/4" dip to each side (span of just over 3 feet from high to low peaks. It isn't super noticeable, only from using a 6' level and drill bits have I been able to find this. Floor tiles to be laid are larger format 12"x24" tiles. Original plan was Ditra decoupling membrane. Q1: Remove Subfloor? - As mentioned previously I was on the fence about replacing the subfloor around the toilet and shower. Due to a slightly wider tub I need to re-do the tub drain and p-trap to gain an inch away from the wall. At first I thought this was the final straw to push me to remove the blackened OSB, enjoy the extra space for plumbing, and replace with new stuff. However, the sub continues below the floor plate of the side wall. Furthermore, the last floor joist I have is just under 4" away from the wall. I could cut the OSB along the plate, but this would result in some overhang (and possible deflection). Furthermore the greywater plumbing travels in this joist space right along the side wall, so I could not simply sister the joist. I COULD stick a 2x4 or something in there horizontally (4" side flush to the floor), and secure it at a 90 to the joist by screwing through the joist. It wouldn't be super strong as it is clearly weak to any torque force, but possibly enough to simply provide a little extra support to avoid deflection? Maybe subfloor needs to be thicker anyways and this 4" overhang is nothing. Q2: Level? - Previous jobs were for LVP where I'm looking for a tolerance of 1/8". Is 1/4" something I can either just work with, or try to at least reduce with a little extra mortar in the affected dips? Should I be using self leveler as first step floor prep (have experience with this and aware of the steps). Yes I realize best practice is probably shave that joist down but I'm apprehensive about this as a diy'er. If I did do self leveler, I'm unsure how this affects Q1 re: subfloor required thickness. Photo's added for context. Hopefully this wasn't too much of a wall of text. For all those who managed to read through it all and especially those who reply, I thank you so much in advance. Basic layoud Wood rot? 3 1/4\" run to wall overhang? 1/4\" dip in level submitted by /u/Anne_8788 [link] [comments]

Mar 19, 2025 - 14:28

I've seen so much conflicting information out there so hoping to consolidate everything here. I've got a few questions related to preparing my floor for an ongoing bathroom reno. Will try to keep concise and itemized to the few questions. If anyone were able to read just one of the questions and reply it would be appreciated. I decided on this approach rather than spamming the subreddit with multiple similar-ish posts

Background:

Ongoing demo. This is a second floor bath above a finished dining room (at all costs would rather avoid accessing from below). Existing subfloor is 3/4" OSB(? could be ply for all I honestly know?). Took off top layer of 1/8" ply that was definitely rotted (not shown). The existing sub shows some old signs of water damage around the tub and toilet area. Still quite firm. Am undecided between treating with some bleach to kill anything there and leave it as is, or rip out (more details later).

My floor joists are a solid 2x10's at 14" on center spans (not standard 16 which is nice). Currently the floor has no deflection (play?) when walking or jumping on it. It does however have an issue with level. What I assume is one proud joist through the middle of the floor (or the house settling from framed walls) has caused a peak in the middle of the floor with just a hair over a 1/4" dip to each side (span of just over 3 feet from high to low peaks. It isn't super noticeable, only from using a 6' level and drill bits have I been able to find this.

Floor tiles to be laid are larger format 12"x24" tiles. Original plan was Ditra decoupling membrane.

Q1: Remove Subfloor? - As mentioned previously I was on the fence about replacing the subfloor around the toilet and shower. Due to a slightly wider tub I need to re-do the tub drain and p-trap to gain an inch away from the wall. At first I thought this was the final straw to push me to remove the blackened OSB, enjoy the extra space for plumbing, and replace with new stuff. However, the sub continues below the floor plate of the side wall. Furthermore, the last floor joist I have is just under 4" away from the wall. I could cut the OSB along the plate, but this would result in some overhang (and possible deflection). Furthermore the greywater plumbing travels in this joist space right along the side wall, so I could not simply sister the joist. I COULD stick a 2x4 or something in there horizontally (4" side flush to the floor), and secure it at a 90 to the joist by screwing through the joist. It wouldn't be super strong as it is clearly weak to any torque force, but possibly enough to simply provide a little extra support to avoid deflection? Maybe subfloor needs to be thicker anyways and this 4" overhang is nothing.

Q2: Level? - Previous jobs were for LVP where I'm looking for a tolerance of 1/8". Is 1/4" something I can either just work with, or try to at least reduce with a little extra mortar in the affected dips? Should I be using self leveler as first step floor prep (have experience with this and aware of the steps). Yes I realize best practice is probably shave that joist down but I'm apprehensive about this as a diy'er. If I did do self leveler, I'm unsure how this affects Q1 re: subfloor required thickness.

Photo's added for context. Hopefully this wasn't too much of a wall of text. For all those who managed to read through it all and especially those who reply, I thank you so much in advance.

Basic layoud

Wood rot?

3 1/4\" run to wall overhang?

1/4\" dip in level

submitted by /u/Anne_8788
[link] [comments]