Replacing OSB subfloor with three-quarter inch ply?

[Stoneface]

Okay, here's the deal. The place I'm buying has a shop the old owner started to build, then just left. He got married and moved away. That was five years ago and the place has held up great to everything, including some pretty gnarly winters with feet and feet of snow on the roof. The framing is solid. He poured footers and did a common pier and beam foundation, but he ONLY framed it up and tacked OSB to the foundation, walls and roof. Now it's been rained on for five years and the subfloor is giving in. So, I want to finish the building, but am not sure to go about replacing the portion of the subfloor under the walls. The floor is 5/8 OSB and I want to replace it with 3/4 ply. The shop is small, maybe about 12x10, but I don't want to take it all down for something this simple. I can replace the rest of the subfloor, just not sure how to go about the portion under the wall. I was thinking about taking a saw zaw to one half of the building (leave the second half intact so it doesn't fall off the foundation) to cut the nails loose so the framing isn't attached to the foundation, then jack it up, slide the 3/4 under the wall, then lower it and repeat on the other it. I've also thought about just using shims, but not sure if that would be feasible.

Any thoughts?

[mountaindogs]

For the floors I would replace with advantek OSB. I think it will be alot less likely to warp and buckle over time.

[Ruffshooter]

It would be helpful to post photos.

But, Is the OSB actually nailed to the concrete or to the framing that sits on the concrete?

One Before residing to replacing what is under the walls, What type OSB, Is it advantec or another exterior type sheathing?
Second, test what is under neath.

Take your skill saw set it to depth of 5/8" and cut along the wall, remove the section, Just to check and see if it is punky or not under the wall. If it is. and you need to remove it, just go in 8'-0" increments and cut nails with a reciprocating saw over the sheathing under the bottom plate of the wall and below the sheathing and above the framing, then remove the 8'-0" section.

You can replace with the 5/8" plywood or Advantec: (Advantec is a better product than plywood for a subfloor) as a sub floor then a 1/2" layer of UL plywood over that. Glue your sub-floor. You should be able to work the plywood under the plate if you got the nails an wood out.

Without photos or being there, there may be other ways to do it.

[Stoneface]

There are poured footers with block on top of them and the floor's frame is wresting on the blocks.

I've never heard of Advantec. This stuff is just the standard particle board you buy when you want something cheap. The subfloor especially under the window and door openings are rotted and weak. The floor joists solid.

So, you're saying to pull up this particle board then laying some 5/8 Advantec then another 1/2 underlayment? But, the underlayment wouldn't go under the studs, right? They'd go over the subfloor, between the framed walls? What makes Advantec so much better than even plywood?

I'll post some photos of it when I get a chance.

[ACooper]

http://www.contractortalk.com/index.php

[Ruffshooter]

There are poured footers with block on top of them and the floor's frame is wresting on the blocks.

I've never heard of Advantec. This stuff is just the standard particle board you buy when you want something cheap. The subfloor especially under the window and door openings are rotted and weak. The floor joists solid.

So, you're saying to pull up this particle board then laying some 5/8 Advantec then another 1/2 underlayment? But, the underlayment wouldn't go under the studs, right? They'd go over the subfloor, between the framed walls? What makes Advantec so much better than even plywood?

I'll post some photos of it when I get a chance.

So if rotten then definitely remove the standard OSB.
The Advantec and the GP version of it has a much more water/moisture resistant glue.
The underlayment plywood would not go under the studs. so you are correct. This is a standard practice.
Just do this in sections, It will be time consuming and may take a few beers at the end of the day to get over it.

I am kind of curious how the bottom plate could possibly be in good shape and not rotten also. If the plywood is rotten then the bottom plate of the wall probably is or is headed that way. Probably mildewed and moldy.

If this is the case then you could snip off the nails at the stud and plate remove the plate and ply wood with the earlier suggestion and replace both. This would be easier than just removing the plywood from under the plate.

Rick

[Stoneface]

I haven't done an in-depth inspection of the whole structure, but from what I have seen it looks and feels solid. I'll get up under it with a flashlight and crawl around to see if I can find any issues with the plate or anything else. If it's just some surface mildew or mold a good bleaching should do the trick, I'd imagine. If the structural integrity isn't there I'll replace it. Thanks for the heads up.

I've done some research on Advantech material. That stuff is pretty slick! I tried to find the Georgia Pacific equivalent, but the only thing I could find was something called Plytanium. It's not an OSB, it's an altered plywood. Is this the stuff you're talking about? How does it stack up to Advantech?

Home Depot Has Advantech a couple bucks cheaper than Lowe's, but they also have the same exact thing - 23/32 Advantech - available in a tongue and groove option for $6 less per sheet. I've never messed with anything tongue-and-groove before. Is it suggested?

[brad27]

T&G is better. Don't nail it down, use screws.

[Ruffshooter]

T&G is better:
Do not use a drywall screw, use a deck screw. The heads can pop off drywall screws on a floor.
Also, you generally will glue the plywood down with a subfloor adhesive. If using a air framing gun or gas powered nail gun, when glueing the floor a galvanized 8d ring shank nail works well and is fast and less expensive than screws.

The plate I am speaking of is the at the bottom of the studs where the bottom of the wall and the floor meet. (Unless you have a balloon framed building. i.e. the wall framing goes down to the top of the foundation and the floor box sill is nailed to the wall studs. I doubt you have that.)

I would get that plywood off the floor framing and let the top of the joist dry out before putting more material over it. Does this have a solid roof on it now?

Rick

[Stoneface]

I know the plate you're talking about.

The roof is not solid. The guy poured the footers, set up the blocks, framed the foundation, sheeted it, framed the walls and roof and sheeted them, all with OSB. The OSB is terrible now. He's leaving a mess of steel paneling and "built" a tiny "house" that didn't turn out too great, so I'll take from it to build/finish other buildings. I thought since the walls I'll be replacing the subfloor under are the only ones supporting the roof I wouldn't want any more weight up there than had to be, especially when I'm I'm going to be trying to squeeze 23/32 board into a space that is right now at 5/8, maybe more since the OSB has gotten wet and rotted.

The guy is starting to get cold feet, I think. He's had awhile to get an agreement drawn up and sent to me for review before I head out for his place tonight to make it official. I sent him a message this morning and he said he hasn't even started it and would get back to me to let me know where he stands.

[DonF]

What is between the sub floor and the blocks? If nothing, I would walk away! You could use post's and beams to raise and hold up the wall on bearing walls But what would have when your finished? Contractor to do it would probably cost quite a bit. if you did raise the walls and remove the sub floor, you probably need to put in either green plate or roofing felt between the un-treated wood and the block wall. Sounds like there is a post and beam floor also. The post's either should be sitting on a concrete pad with felt between the post and pads. As long as you don't get in that far you might not have to come up to code, if that is code there. You might check with the building inspector to find out what ir required there.

[Stoneface]

The foundation is a basic pier and beam setup. Like this:



In any event, the guy eMailed me the agreement he came up with and he must be out of his fricken mind. His terms are way beyond what I would consider. I'm going to try and negotiate, but I have a feeling he won't budge. Oh well... and this was a good property, too.