First off: A huge Thank You to Ken, for starting this site, and to all those who have posted such great knowledge. I have learned an incredible amount that, normally, only years of experience would bring.

I have read, well nearly, this entire sight in the past 4 months. Outstanding stuff. My 3.7 tons of tiete rosewood will arrive next week and I believe I have all the bases covered, mostly thanks to the great posts here.

Except for one.

My subfloor, in a 1991 built house, is OSB and stamped "APA Rated Sturd-I-floor, 23/32 thick, Exposure 1 rated, PRP-108"

Everything I can find, though the information is rare, seems to state that the PS2 rating is equal to the PRP-108 rating. At least as far as hardwood installations go.

My intent is to use cleats (powernail L cleats in a bostitch manual nailer; fun) to go directly to the OSB with #30 felt between the flooring and the subfloor.

There have been statements that 'old' OSB is 'not so good' and I'm trying to determine if my subfloor fits into that category.

Thank you, one and all, for your graciousness in posting your experience.

I'll bump my own post just in case someone with the answer missed it and to restate the question a bit differently.

Is PRP-108 sturd-i-floor rated OSB the same as PS2 rated OSB? As far as hardwood flooring is concerned, of course.

According to the APA site it is, but I have found very few other references to the stuff.

The manufacturer is the one to answer your question. In a study performed by Virginia Technical Institute, 3/4" OSB performed about the same as 5/8" plywood subflooring. It is an accepted subfloor/underlayment per NOFMA. Is it the best? No. But should be fine IF the subfloor is FLAT, well attached and seams are gapped and flush. Sanding the seams is usually required on OSB. Be sure to lay the flooring at 90 degrees to the trusses/joists. Alternately, you can lay the flooring at 45 degrees. Just not parallel unless you add additional blocking or more plywood. Please read:

http://www.nofma.org/Portals/0/Publicat ... Report.pdf
http://www.nofma.org/Portals/0/Publicat ... Floors.pdf

The installation guide I have read numerous times, but I hadn't looked at the subfloor test document.

The manufacturers document states that the prp-108 rating is equivalent to ps2 for hardwood installs.

Everything will be laid at 90 to the joist, subfloor will be extremely flat, once I get done with it, and all moisture levels will be correct.

Much thanks to you for the documentation and for your experience.

I have this same subfloor in my house. Since I need to run parallel to my joists...I will be putting an additional plywood down.

I may have already asked a couple of these questions, but cant seem to find them.

Questions:
1.) What kind of plywood?
2.) What is the minimum thickness?
3.) Tongue and Groove?
4.) What size screw to fasten?
5.) Do I also need to aclimate the plywood before laying down
6.) How soon can I start laying the planks?

Some guys use CDX grade plywood, I prefer the BC underlayment grade myself. You want a square edge, not T&G. Thickness would depend on what your subfloor is, but 1/2" is usually recommended to run parallel. Screws should not penetrate both layers, so don't try to hit any joist installing underlayments. Leave an 1/8" gap all round the perimeters and keep the UL staggered from the subfloor seams, direction does not matter if installing hardwood (direction does matter for tile). Screw it about 8" OC around the perimeters and 10-12" OC out in the field. If the UL is stored and kept dry it is pretty much good to go. I have stuck my meter in the "UL" sitting in Lowe's and it reads OK, around 8-9 %. If you don't have a meter waiting a few days would be advised.

The first thing to do is get your subfloor in shape before its covered over. Re-nail or screw it, sand the seams, check for flatness, fix squeaks, ect. Get that right then put down the UL.

Thanks so much...very helpful

If we do not have a meter for moisture reading, can we simply say to let the wood (underlayment AND hardwood 3/4") acclimate for 3-5 days? (I am in no real hurry as this is a DIY job)

Let's limit this answer to an occupied house that you already live in, you ought to be safe on both counts.

True, this is an already occupied house.

So, if I have about 200 tiles to lay in. Can I do this while the wood is acclimating. Perhaps wait 3-5 days after I finish up the tile job? (I am worried that excess moisture from the tile job will create problems) Or is this too small of a job to worry about it?

Well, it is a crap shoot without a moisture meter. You realize you would be "guessing" and "assuming" everything is A-OK. It's your home and your wood. All guidelines recommend checking the moisture content prior to installing wood flooring. It could turn out just fine. Then again, maybe not. Without a moisture check, how do you know for sure?

Harbor Freight sells real cheap moisture meters, they should be close enough to tell you something. Any meter would be better than having to guess.