Repairing subfloor

[iamwiz82]

Some background, this is a 1940s ranch on a crawl space. I recently began to tackle my mud room which has always had questionable quality linoleum in it. The mudroom hangs off the back of the house and I do not believe it was part of the original build, though the person I met who grew up in the house (born in 1952) always knew the room to exist as it is. It has three exterior walls and one wall shares with the original exterior cinderblock wall of the house itself, so it is essentially separated from the rest of the building.

I pulled up the 90s era flooring to find portions of the subfloor not in great condition. It appears that when the vinyl was done at least one full 4'x8' sheet of plywood was replaced by the exterior door, but the rest appears very, very old. they are in 2'x4' sections. I took a core sample and everything is true 1" in thickness. Joists feel OK so far.

So this leads to my question. I took a look at the local big box stores for options for 1" actual and came up with nothing outside of double stacking 1/2" or 3/4" and 1/4" sheets. Is this ok to do for subfloor patching? I am not liking the idea of having the seams match up however I am not seeing many other solutions outside of ripping the entire floor up. I'm pressed for time to get the project done, however.

 

[DrPizza]

I think 2 1/2" sheets, laminated together would work. Make sure to glue them together with a good glue, thoroughly covering the surface, else you will likely end up with squeaking. And, it's probably best to orient them 90 degrees from one another so the grain alternates in direction. That won't be as strong as 1" plywood, but should be strong enough for a subfloor (normally 3/4" I think, hence you didn't find 1" for sale.)

 

[NutBucket]

And use screws to secure the plywood. You could glue/screw one layer and then glue/screw the second layer. That would be the overkill (but squeak-free) method.

 

[Howard]

Go big or go home

http://myhuberwood.com/main.aspx?pagename=advanTechSheathingSpec

 

[skyking]

double layered 1/2 ends up being stronger than a 1" If you mix the joints, use good glue and ringshank nails to laminate it.
The key is mixing the joints. Plywood squeaks at two places, on the edges and loose fasteners out in the field. The loose fasteners are often due to poor joists, not straight or weak and allowing a lot of movement.
One of the problems with a scabbed-on porch on block footing is proper ventilation. while you are stripped down address that, and add a modern plastic vapor barrier. If it is cold where you live, consider adding 2" foam insulation around the outward facing 3 walls.

 

[iamwiz82]

So my problem has "solved" itself. While cutting out a bad section I attempted to pry out at a seam and it wouldn't budge expect for the top 1/4". It turns out that at some point a 1/4" of plywood (or Lauan, judging by it's failure)over top of the existing subfloor and glued the heck out of it, then nailed it down. After a test rip of the 1/4" stuff the real subfloor is nearly perfect, other than the cuts and cores I made :/.

 

[iamwiz82]

double layered 1/2 ends up being stronger than a 1" If you mix the joints, use good glue and ringshank nails to laminate it.
The key is mixing the joints. Plywood squeaks at two places, on the edges and loose fasteners out in the field. The loose fasteners are often due to poor joists, not straight or weak and allowing a lot of movement.
One of the problems with a scabbed-on porch on block footing is proper ventilation. while you are stripped down address that, and add a modern plastic vapor barrier. If it is cold where you live, consider adding 2" foam insulation around the outward facing 3 walls.

I had planned on that as I had done the rest of the house using 10mil vapor barrier and lots of foundation pins last year, but someone had beaten me to the punch here. They dumped cement and then laid vapor barrier that is actually attached to the foundation.