Repairing Water Damaged Subflooring

ntl1991December 13, 2010

When I purchased my house, there were a couple of places were there had been water damage from a leaky steam radiator and the bathroom tub. The water damage only affected the sub floor and not the joists, and since I hadn't lived here (the apartment was rented out), I forgot about the issue. Now that I am living here, its one more thing on my list.

The old sub floor looks like 1x8. The worst area is next to the bathtub. It's actually under a closet wall for the bedroom next to the bathroom. If you put weight over the area, a gap appears below the baseboard trim.

My plan is to replace it from the bottom by cutting out the rotted area so it's square, and cut sections of 3/4" or 1/2" plywood to fit between the 12" OC 2x8 floor joists, and then support the plywood with blocking between the joists. The finished floor is original hardwood and it really isn't an option to rip it up and replace the sub floor from above. The closet wall is NOT load bearing, just a partition wall.

Attached are pictures.

Anyone had to deal with this same situation? Any tips or tricks? Advice? Have I gone mad?

Bathroom/Closet floor:

Living Room Entry (Leaky Radiator):

(*please disregard the plywood with insulation attached to the bottom of the floor. This is to block the hole which an old steam pipe passed through for the radiator. (I now have a baseboard hot water system) A faux register vent was attached to the top of the floor.)

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I have a similar situation right now. In my case I have the bath gutted , but my earlier resolution proved futile.Similar to what you suggested I did several years ago. From underneath I fitted .75" marine ply and 1.38" screws, along with 2x4's attached to the joists, under the ply. The bath had a mosaic tile set in mud. It held for a while, which I hoped for. But I knew this was only a temp fix.
I know you hate to lose the hardwood floor or should I say doing all the work to reinstall it, but if you have any intents to stay a while , go the long way. I just finished a bath directly below this one, I'll try to post photos of existing condition in the upper bath.

    Bookmark   December 14, 2010 at 6:23PM
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This is a classic case of do it right or do it over.

I don't know how you would cut out the subfloor from below, particularly if the hardwood floor is nailed/stapled to the subfloor.

And cutting out the visible subfloor still leaves the part sitting on top of the joists---which is the bigger problem area in terms of support.

In short, what you propose is a very bad idea that will be even more expensive than repairing it right the first time.

    Bookmark   December 14, 2010 at 8:55PM
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If the finish floor is hardwood it is nailed to the sub-floor.

You are proposing a very poor fix that will leave damaged material on the top of the joists, and likely very hard to do.

It is not that hard to take up a few floor planks to repair under them, then replace them.

The old sub-floor may be 1x8 or even a full inch thick (5/4 wood or rough cut).

    Bookmark   December 15, 2010 at 2:51PM
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Upon taking a better look at the pix, this house is not that old. The tell tale is the planed framing members and the blocking.My current house ,59', has bridging, rough cut strapping. If you look at the sub floor in the last pix , the planing marks are obvious
(right). The mid section shows signs of poly.Whats on the ply in the last bay. Seems to me this was repaired (half ass) before.Bottom line, all materials for this repair are off the shelf.You did mention this was rental property at one time.Save yourself from potential grief.

    Bookmark   December 17, 2010 at 7:47PM
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By now, you have picked up on "dont do it"... So looking at the brightside- Carefully tearing out your nice wood floor (from above) you can reuse it or keep it for another project(s). Tearing it all out gives you options you wouldnt have had before. You can adjust your sink or toilet locations, move the bath if you like... Change the size of that closet... Get you some more room in the bath if needed.Or just change the floorplan. PLUS you can then finish it off with a desireable tile floor. Proper installation is very easy DIY project just get a video at a home center and take a look. You will see it isnt that bad..Good luck & hang in there.. Two things I have learned about home repairs is
1)Do not remove protective guards off saws (dont ask)&
2)A cat turd dipped on chocolate- is still a cat turd..

    Bookmark   December 23, 2010 at 9:38AM
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