Fixing a subfloor

[suburbanite]

My parents are visiting relatives until the end of January.

Meanwhile, for several years one area of the bathroom has been subject to tub-splash, such that the subfloor next to the tub under the linoleum feels 'spongy' when you walk on it.

The house is a one-story house with no basement, only a crawl-space beneath.

Any ideas what kind of repair might be required? Has anyone repaired the floor of a 1970's era tract house before?

I am considering whether this might be a project that I can do for them as a surprise for them when they return home; it has been a worsening problem for years. Also they've been wanting to re-do that bathroom anyway and this would let me put in a faux-travertine tile that I think will give them the look they want without the maintenance requirements of real stone--to upgrade instead of the 36 year old linoleum currently there. They keep talking about it and never actually do it...

Since the spongyness extends right up to the tub edge, do you think repairing this would require removing the tub? Also, what about the adjacent wall, as the spongyness meets the foot of the wall (though the wall isn't spongy).

[dirty]

i could take a guess. however to get a good idea of how much work needs to be done you'll need to crawl under the house. if your lucky the floor joists will be in decent condition and only the plywood is water damaged. yes i think the tub will probably need to be moved. with the kind of movement you are describing i bet water got under the tub.

[bare]

Piece of cake, day's work. Locate the joists with a stud finder, set your skillsaw to 3/4 inch and cut out what you need to to get to solid wood on joist centers, and your sawzall to go along the tub. Once you've got the floor joists exposed you can check them out for damage and sister them up as necessary. Add one to the area under the tub so that your new floor has support and anyplace else necessary. Cut and screw your replacement 3/4 plywood. Put down your finish floor, grout, seal and caulk the heck out of it so it doesn't happen again.

[insanity]

Id definitely go under the house to have a look first. Take along something to poke at the floor and floor joist with like a knife or flat tip screw driver. You ll be surprised at what might be dry but rotten.
Id also bet its rotten a bit under the tub. How bad or far is the question. Most likely you can leave the tub in.
But no it isn't to hard to do with a little basic carpentry knowledge.

As said make sure all butt joints fall on the floor joist even if you have to add a couple. Sister up any that don't look to good. Add support column of cement blocks if in doubt. Might even add one anyway since your considering tile.

You can drill a hole in a (firm spot!) in the floor (big enough to stick your tape measure threw) to get an idea how thick and what type the sub flooring is. As it might take some figuring to match up the thickness. Considering its age. They often used double layers of sub flooring for kitchens and baths back then.

Firm spot= an area not touched by water. As the water will have caused the wood to swell, and your measurements to be off a bit.

[suburbanite]

It looks okay from underneath. It feels spongy under the vinyl flooring from the top, so I'm assuming that's the wood in addition to whatever underlayment is under the vinyl. My dad insists it is just the underlayment but I want to be prepared to deal with whatever shows up when the vinyl is removed.

[insanity]

The underlayment is probably that old particle board (looks like saw dust chips) crap they used back then. I hate that stuff. I still cant under stand why they covered the ply wood with that stuff back then. Id rather have bowed floors than weak floors.
Its most likely also 3/4 inch if its that stuff. You might could just cut it all out and leave the sub floor if it is two layers. And then lay the concrete backer board for the tile in its place. They lay it over just the OSB in new homes.

Its a nasty dirty job but you can do it!
You might want to get a roll of plastic to cover the entry way to the bath or hall. To keep the dust out of the rest of the house.