View Full Version : Repairing Bathroom Subfloor

03-23-2008, 12:28 PM
This is my first post although I've read a lot on here and appreciate the great dialogue. I am fairly competent with tools. I have a problem I'm trying to solve in a bathroom and I would appreciate some input and feedback. Let me start by saying what I'm looking to do, then add some commentary.

To repair some water damage, I want to:

1. Fix/replace damaged subfloor, if needed.
2. Replace damaged closet flange, if necessary.
3. Lay 1/2" of plywood over OSB, then backerboard and tile. (Wife doesn't want vinyl again!)
4. Replace current 12" rough-in toilet with 10" model.

There was a slow toilet leak in one of the upstairs bathrooms in our 12 year old house. The wax ring was evidently compromised and went unnoticed until a lot of water appeared on the kitchen ceiling. It's not the first time it had leaked but it's the most significant.

I pulled up the toilet, replaced the ring, reset the toilet and things seemed okay until I tightened down the toilet bolts to the flange. The more I tightened, the more the toilet settled into the flooring. I knew right away the subfloor under the sheet vinyl was wet and spongy. This was right before Christmas. I put a bead of caulk around the toilet and let it be. Cosmetically, it looked okay except you could see that the floor was depressed ever so slightly at the base of the toilet.

Let me also mention at this point that the other three bathrooms in the house are all plumbed/framed for 12" to 13" rough-in from the finished wall. However, this one is barely over 10" but they still used the 12" toilet. I had to cheat on the tank to get it set but I think this has been the root of the leakage problems over the years.

By the way, I hit the kitchen ceiling with Kilz, let it dry for a couple weeks and actually repainted the entire ceiling in the kitchen and adjacent living room since I couldn't get the "damaged" area to match up colorwise with the rest due to age, dust, etc. Now THAT was a fun job on the popcorn ceiling.

Skip forward to this week. We've been thinking about options for selling the house and that bathroom floor came to mind. I knew I had to do something so I pulled the toilet and ripped up the vinyl to expose the 3/4" OSB. Well, the flooring around the toilet was dry but flaky and certainly not strong and level. I also discovered there was a wet area at the corner of the floor near the tub and it looks like some water has been seeping ouit from the seam in the sliding door channel and saturating the floor. I've let it dry a few days and it doesn't appear to have lost substantial strength in that location.

The closet flange is also somewhat rusted out and the bolt slots are deteriorated.

I questioned whether to replace the OSB at all or just fill it in and put a new layer of plywood down. However, that just opens up potential problems and I'd prefer to do it right even though the existing area is dried out and seems relatively strong. Replacing the OSB isn't a huge problem in open areas between trusses. (I only want to replace the damaged part.) The bathroom is 5'x10.5' and the floor trusses run parallel to the long dimension. They are bottom-bearing 2x4 web trusses, 3-1/2" wide and about 14" tall. Span is about 15 feet from the outside wall to a carrying wall in the middle of the house and about 30 feet overall. I've drawn approximate locations into two of the attached photos. There's one sort of down the middle and one to the right that appears to hit right at the toilet flange. The next one going toward the wall behind the toilet is in the adjacent bedroom. Going to the left of the center joist, it appears to be right under the wall on the left side of the bathroom.

If I cut out the bad stuff around the toilet, I'm okay on the front side since I can split the center truss and fully span the one by the flange. However, there's nothing behind the toilet to nail into as the truss is in the next room. Unless and until I rip up the subfloor, I won't know if any additional bracing is provided between the trusses to further support the toilet and waste pipe. I could see about attaching some joist hangers and creating a nailing plate somewhere between the flange and the wall in order to give it strength but that would require dropping some of the kitchen ceiling for access. I could also drop 2" screws into a flat 2x4 on each side of the cutout for some strength.

If I get the subfloor section ripped out, I should have enough room from above to cut the flange and extend the waste pipe higher so I can put a clean layer of plywood down and then flooring material. One thought is to replace the bad subfloor, add a layer of 1/2" plywood and Hardiboard, then lay ceramic tile.

Back to my original points...

1. Am I on the right track for wanting to replace the subfloor or do I have any good alternatives?

2. Is there an easier way to replace the closet flange and waste pipe other than getting in there, cutting the old off, adding a repair hub and a longer 3" pipe?

3. If I were going to lay 1/2" plywood (don't want to do 3/4" due to height issues compared to carpeted hallway) over the existing OSB (including the damaged area), would I be open to problems around the flange or would it be strong enough to carry the weight of the toilet since I'd be adding that and the backerboard? I'm not advocating doing a hack job and simply covering up problem areas--just exploring all options.

(By the way, I also realize it would be a good idea to inspect the truss wood if it's been leaked on next to the flange for any length of time.)

4. I still think I probably need to swap out the toilet as I'm not sure if there's room at the truss to gain the extra 2" from an offset flange without compromising the strength of the truss if I cut into the top chord.

I guess I'm trying to save some hassles by doing all the work from above. On the other hand, perhaps it's cheaper over the long run to just cut the kitchen ceiling for full access and then repair it, too.

I'm open to any suggestions or insights on this. Thanks for a great site. Photos are below.

John from Dallas






03-23-2008, 03:01 PM
If the OSB is spongy or swollen, it should go. Trusses are generally engineered for an L/480 rating, so while you should verify that with the manufacturer, you should be okay for ceramic, but not stone tile. Any subfloor works best if it covers at least two joist/truss bay - that keeps the ends from trying to pull out of the end as it flexes inbetween.

If you are going to remove the subflooring to replace, you may be able to extend the drain to allow use of a standard 12" rough-in toilet. This will give you a greater selection at a lower cost. You didn't mention the spacing of the trusses...if they are at 19.2 or 24", then you'll want two layers of subflooring to support your tile. A second layer is always useful (except for the height!) to stiffen up the subflooring for tile.

I'd want to use some blocking so the edges of the subflooring are supported. You should probably contact the truss manufacturer to discover the proper technique to not compromise them.

Check out www.johnbridge.com (http://www.johnbridge.com) for help in tiling. Especially in smaller rooms where the difference in cost is minimal, an antifracture membrane makes a lot of sense, especially where it can get wet - they allow you to essentially waterproof the subfloor. I've used and like Ditra from www.schluter.com (http://www.schluter.com). Neat stuff, and easier to carry, cut, and install than any cbu. Hardieboard is a fine material and you can successfully use that as well, but look into Ditra...I think you'll like it.

03-23-2008, 04:27 PM

Thanks for the reply. I figured I'd end up leaving some info out.

The trusses are on 24" centers so there's no way for me to span that last section under the wall unless I cut out a section under the wall and into the next room, then try to slide a piece of OSB under the wall. I might just have to create some blocking on that end. If I come up from underneath, I could see about tying a cross member between the two trusses and nail into it.

If I go to a second layer of plywood over the OSB, I'll probably pull out the vanity and cover the whole floor with the grain running the same direction as the OSB but offsetting the boards and use screws along that back wall and toilet area. You're right about the height--I'll have to transition from the carpet in the hallway to the 1" vertical rise in the bathroom floor.

I'll give Ditra a look.

BTW, I used to live in Worcester and have been to/through Nashua many times. Good to touch base with someone from the "old country."


03-25-2008, 06:02 PM
You have gone this far!Open up and set your toilet outlet to receive a reg.
12" rough in so if you get sick of the toilet in the future your not married to the 10"
Rough in.And...
Good luck!

03-26-2008, 05:01 AM
By the looks of the floor joist location, he can't move the flange out any further.

You have gone this far!Open up and set your toilet outlet to receive a reg.
12" rough in so if you get sick of the toilet in the future your not married to the 10"
Rough in.And...
Good luck!

03-26-2008, 11:41 PM
By the looks of the floor joist location, he can't move the flange out any further.

On Friday, I'm going to pull up a section of the OSB about 18" wide and from the left hand floor truss to about halfway between the current closet flange and the back wall. This will be around 30". As loafer said, I doubt there's a lot of room to move the flange out but I'll know better once I pull the floor.

I still haven't decided if I'm going to tile or just put down some new vinyl since we're going to put the house on the market. That's a decision I can make without much trouble. I would like to know if it's better to make sure of my measurements and make the cut on the waste pipe before doing all the flooring or if it's better to leave a longer length, install the flooring, then cut it down for installing the flange. My guess is the first option but wanted to see what thoughts were out there for proper installation.

03-27-2008, 06:38 AM
Is it a 3" or 4" pipe? If 4", leave it long, cut it off flush with the finished floor which can butt up right to the pipe, then use an internal flange.

If it is 3", you can also leave it long, but since it needs to be cut off below the floor, you need a means to cut it off...they make an internal cutter designed for that. I've used my dremel tool, but then you're intimate with the floor for awhile while you do it. Also, on a 3" pipe, you need to leave a space around the pipe to allow for the externally mounted flange to slide down over the outside of the pipe while still allowing enough subflooring there to catch the anchor fasteners (screws) to hold it in place.

03-27-2008, 04:34 PM
It's a 3" pipe with a 4x3 flange fused around the outside. I'll leave the gap around the new pipe when I set the new flooring.

03-27-2008, 05:03 PM
You can leave the vertical pipe unglued until you are ready to set the flange...cap it while doing your work, then measure carefully, glue and set the pipe and the flange at the same time. This way, you are pretty much assured to get the flange to set flat on the floor properly. You have to make sure the fitting is not going to move as you try to push the piece in place...it may need some blocking or a shim to hold it in place. 3" pipe may need to be held for awhile to completely set up...the taper in the fitting can push it back out a ways if you don't watch what you've got.

03-28-2008, 01:42 PM
Well, I had a bit of good fortune when I ripped up the subfloor. The floor trust behind the toilet was not in the next room on a 24" center. They actually put one on a 13" center that allowed me to cut the OSB partway across the top of the truss and not have to go all the way to the wall. Whew!

When I put the new subfloor patch in, this will allow me to span two full truss spaces and have room to anchor both ends. I'm going to sister some 2x2's on each of the trusses just to have some extra area to bite into. I'll also put some blocking under each of the sides using 2x3s or 2x4s perpendicular to the trusses and attach with Liquid Nails and screws just to firm it up.

Along the tub side of the current hole, there is the groove for the tongue of the OSB. Naturally, this is empty so I'll need to fit a tongue edge in there so it doesn't collapse unless I decide to go with the tile in which case I'll be going over the entire floor with another layer of plywood underlayment and it won't matter.

In answer to a previous comment, the original plumber already cut into the floor truss to install the vertical pipe and flange so there's not much chance of running farther out from the wall. I don't want to compromise the integrity of the top plate of the truss--especially since it's just a single 2x4 and not a double. (Hello, new toilet with 10" rough-in.)

QUESTION: If I want to put a longer 3" riser in to accommodate the tile floor (raising things a total of about an inch), where would be the suggested place to "cut and paste"?
a. Just cut off the flange and replace with a long-neck flange?
b. Cut the current riser a couple inches above elbow, put on a repair joint and a new riser above that?
c. Cut the horizontal waste pipe, attach a new elbow and riser?
d. Other?

Of course, I can keep the current flange in place, scab two pieces of underlayment in around it with bracing across the seam between the trusses and just run with sheet vinyl to get it all done with out having to rip out the vanity which will require modified finish plumbing (no big deal) since everything is soldered copper tubing instead of flex tubing. I can easily do all that. Still, I will have to shut off water, rip things out, put on compression fittings, get new faucets, etc. Not to mention pulling the mirror, 61" vanity top, two cabinets and whatever else comes up.

Here are some updated pics of the project.






03-28-2008, 05:10 PM
You've got enough length to put a coupling in if you cut off the flange. If you cut the riser off near the elbow, you could use a Ram-bit to ream out the fitting and then just install a new riser the proper length. There are some pictures of them on this site.

If you don't want to limit yourself to 'standard' 10" rough-in toilets, you could try one of the Toto models that use the UniFit adapters. While it comes with a 12" rough-in adapter, you can buy a 10" one. Personally, I like the look of those - they have a full skirt which is easier to keep clean, and the lines are nice. I wish they sold the toilet without the adapter packed with it, then you chose the one you need rather than making you buy a second one, if it isn't 12", though.

03-29-2008, 10:48 AM
Jim, thanks for the reminder about the Ram-Bit. I called Economy Plumbing Supply here in Dallas and they had a similar item called the Socket Saver by Plumbest/Jones Stephens Corp and it was only $22 plus tax. (UPC 717510443004). I think it is probably available at a nearby Do It Best hardware store since they list it in their online catalog but I opted to try the plumbing supply first.

I cut the flange off, then cut the closet stub/riser off at the 90 elbow and in less than 3 minutes with my 1/2" drill, I had the elbow reamed out and ready to put in a new length of 3" PVC. I'm going to brace under the elbow between the trusses since I can't reach up from the ceiling below, then set my new OSB patch and put in the PVC stub. After I do my flooring, I'll cut the PVC stub to the proper height and attach the flange.

The help on here has been great. I'll post some photos after I get done.

05-01-2008, 02:42 PM
Well, I figured I ought to put a final note on here that the project is complete. With travel schedule, I had to do it over several weekends. Additionally, I went ahead with doing vinyl instead of tile and just had a local guy install it for $50 since he was replacing a section of carpet for me.

After putting in the new section of OSB, I set the new waste pipe in the elbow and it came up to the bottom of the OSB. After the vinyl went in, it was a simple step to put on the flange and get it set flush on top of the new flooring.

Because some of the old OSB had swollen from prior water damage, my setting area was about 1/8" off level so I shimmed the back of the toilet with composite shims I got at HD. Slid them in until snug and then just lifted to snap off the excess. Great suggestion from you guys!

I'd asked about possibly going to a 10" rough toilet since I'd had problems with the setback earlier. However, when I had the floor torn out, I was able to cut just a hair more off the truss and bring the waste pipe back about a 1/2" more than it was and the flange could be positioned a little farther from the wall than before. This bought me just enough space that the existing toilet reset fairly well on the new flooring. Granted, the tank is up against the wall but everything is much better.

Got it all back together, including new trim all around, caulked the trim/vinyl and cleaned everything up. I'm especially pleased that it was a DIY even though there were a few challenging spots along the way.

Updated pics are below. Thanks to those of you who contributed on this thread and another I'd posted about setting the flange. I also appreciate the wealth of info in various other posts on the board.

Terry...Special thanks to you for hosting this site. It's fabulous!

05-01-2008, 02:43 PM
More pix...

05-01-2008, 04:15 PM
Nice Job!:D

05-01-2008, 05:02 PM
very nice work, and great reading material hehe :D