Return to the Home Repair Forum | Post a Follow-Up

Rotten bathroom subfloor

Posted by ayasud (My Page) on
Sun, Jun 24, 07 at 1:20

Okay, today I peeled back the bathroom vinyl floor to find a wet, moldy mess! It was literally sopping! Looks like the wax seal around the toilet has been leaking. Lo and behold, the underlayment is PARTICLE BOARD! How is that even legal??

Under the particle board is 1"x5" tongue-n-groove planks on 48" on center joists. There is a joist running down the center of our bathroom- so if I rip out the subfloor I'd have one joist to nail to but couldn't reach the next joists over unless I, oh, knock down some walls.

Add to this I am horribly claustrophobic and while I'm very handy with a circular saw and have a kickass hitachi framing nailer- it is unlikely you'll get me under the house into that crawl space. My husband is an engineer for Google and his comment was: "I'll be happy to fund the project but beyond that, I need to keep all my fingers."

What do I do? Should I leave the subfloor open and see if it dries out? It doesn't seem rotted out- not coming apart like the particle board and the plywood under the vanity was. It isn't sagging or bouncy or anything, but I would hate to cover it back up if that is the wrong thing to do and just end up with more/worse problems down the line.

Follow-Up Postings:

RE: Rotten bathroom subfloor

I am aghast at the 48" center floor joists!!!!!!!

24" center floor joists are not legal---much less double that!!!!!!!

If I were in your situation, I would add 2" by 6"s or 2" by 8"s between the existing joists to frame the bathroom area so you can install new a subfloor---I'd use pressure treated 3/4" plywood. Regular construction grade plywood would be fine also, but the PT would resist any future leakage better and once covered with flooring , pose no threat.(There is little threat anyway, but some folks feel differently.)

Unfortunately, you will have to get into that crawl space---to install the joist hangers on the joists to either side of the one in the bathroom space, but by precutting them and having a bright light----as well as having the old flooring in the bath completely removed---you mighht be able to handle being in the space------you could go in through the bath floor opening which would allow you to set a couple of hangers and stand up---that kinda thing.

RE: Rotten bathroom subfloor

"24" center floor joists are not legal"

Funny, the IRC shows 12, 16, 19.2 and 24 inch joist spacing.
If the house is older or engineered you can even go further.
The floor gets thicker with larger spacings, but they are very doable.

You are going to need to add joists one way or another.
I have even worked on older houses that had crawl spaces so short we had to dig out to get in them for work.
As long as you are well away from any piers or foundation supports you can dig.

RE: Rotten bathroom subfloor

Huh. My dad has been a framer for 40 some odd years and he wasn't surprised at all- the floor is VERY sturdy- I guess the 1x5 tongue and grove was the thing to do back in the day- think it is actually greater than 1", but not sure exactly. If you go under the house, which I won't, there are some big old beams and piers which is what all this flooring is resting on. It is def. not your standard 1x6 holding up the floor.

We've had fans on the stuff all night and it is dry now- I'm just wondering- how do you tell if omething is rotten? It isn't soft at all or anything, no splintering or chnks coming up. But I don't really know?

RE: Rotten bathroom subfloor

If you can stick a screwdriver through it, it is rotten.

If you have the room put pressure treated 3/4" plywood down over the subfloor and you should be good to go for another 50 years.

RE: Rotten bathroom subfloor

Thanks Hendrickus!

So, looks like the subfloor will not need to be replaced. It is solid as a rock and dried out quite nicely. I'm going to treat the wood and then lay exterior grade plywood down.

I went a little crazy and ripped most of the sheetrock off the walls. I demolished the vanity and the tile tub.shower surround. We're going to put in cultured marble in the tub/shower, on the floor and vanity top. I'll probably do something very neutral so it won't have to be torn out again for a good long while.

The plumber comes tomorrow to repipe the bathroom with copper and replace the toilet drain pipe since that seems to have been the source of many of our troubles. After it's repiped, in goes a new tub and toilet and vanity with sink.

I'll be glad when this incidental redmodel is wrapped up!

Fremont, CA

RE: Rotten bathroom subfloor

Hi Amy,
I am really glad I am not the only one having this problem!! Our toilet has also been leaking and the particle board was a mess with water rot and termites!! I ripped out the particle board and the plywood subfloor underneath doesn't appear to be too bad; can't stick a screwdriver through it. We also have support beams under the house about 4 feet apart and while there is one about 1 foot away from the toilet area, the other is 3 feet away in a whole new room! I really need to do a quick fix that will last a decent amount of time since my husband and I are selling and moving. I wanted to know if you laid down plywood on top of the existing plywood subfloor, what kind of plywood you used and what you treated it (or did you treat the subfloor?) with?? Any help from anyone would really be greatly appreciated!!!


RE: Rotten bathroom subfloor (specification)

In reference to the above: did you use plywood over the subfloor in place of particle board and if so, what kind, did you treat that and with what??


RE: Rotten bathroom subfloor

they said they used EXTERIOR GRADE PLYWOOD. in other words pressure treated plywood.

RE: Rotten bathroom subfloor


Just thought I'd jump in here. I believe that exterrior plywood just has a better binder and a wood with a little rot resistance (like fir). For example you could get a 1/2 CDX plywood (house sheathing)- the C and the D are codes for the condition of the surface on each side of the sheet the X is for exterrior. CDX plywood is much cheaper than pressure treated and I imagine a lot less toxic as it is not chemically treated.
I would go with non pressure treated plywood or osb and fix the problem with your toilet.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Home Repair Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here