1. Is there a specific grade/type of plywood I should use if I'm going to replace the OSB?
2. The floor joists change direction between the low and high floor. I'd love to find a way to install the floor so the can be oriented the same way (length-wise with the town home). Perhaps using boards at a 45 deg angle across the bottom floor joists (which run the length of the town home). If not, then so be it.
3. I'll be snagging several of your articles, one of which deals with removing hardwood floors. I'm thinking that if it's my intention to install plywood, I can be far more destructive in my removal process than I would be if I wanted to preserve the subfloor. At a minimum, I won't have to worry about pulling out all the nails.
Just a suggestion but why don't you lobby Eterna to supply you with a "select and better" grade of red oak unfinished strip floor as a replacement for the whole floor ?
The best plywood for subfloor would be 3/4" BC douglas fir plywood and a grade at least CDX. But the same CDX in spruce plywood would be fine also.
Instead of doing these fancy 45 angled floors (looks busy and is a waste of wood) you can install small 2 by 6 or 2 by 8 block across and between the joists about every 16"- 24". Use urethane glue and a pneumatic nailer to get into this tight spot. This is easy in your case because you are blowing out the whole OSB subfloor. You might at the same time shave down any high joist, that will create a hump in the floor again. I should say that 1" plywood (hard to find) is quite stiff, and it would be fine with this stuff to run the hardwood in the same direction as the joists. You could also use two layers of 1/2" ply well glued together. I've done this on my own floor. Both layers have to be nailed through the joist and the top layer has to have short staples (7/8" narrow crown) in between the joists. This is so the two glued layers act like one thick layer.
But be careful when you remove the subfloor not to remove the support under any bearing or non load bearing wall. Sometimes you will find that you have to leave a bit of the old OSB in place because of this. It might be worth consulting a carpenter to at least prepare this. The 2 by 6 blocking will have to support also any left over edge of old OSB.
Try 2 1/2" Spax brand wood screws to fasten the new plywood to the subfloor. Great screws, in that they drill their own pilot hole with a agressive thread design. And of course use a squiggle of urethane adhesive in each and every joist, not more that 20 minutes before installing the plywood. No squeaks EVER.
Oh, and don't buy that squeaks article for removing both layers of floor. It just deals with trying to salvage an old floor without damaging it. On the other hand, if you find that the three bad men (Eterna, shop and installer) won't refund you enough to cover the total costs, you might consider removing the floor more carefully (then the article will discuss tools and methods) so as to salvage maybe 90% of it. Get some additional wood from Eterna, to make up the difference. Install in carefully yourself. Then of course sand the wood smooth and level on site. Bear in mind that you will have to sand off the "micro bevel" (a real misleading promotional term) and you will loose some depth of wood because of this. Mention this also to Eterna, that you will loose about 1/5 of the value of the original wood and that you ought to be compensated for this also. As well as compensation for removal. We charge as much as 2 bucks per square foot to remove and dispose an old hardwood floor. When you see how much work it is and what your land-fill charges if you were to throw the wood away, you'll see why we charge that fee.
I hate to be such a rabble rouser, but I feel it's my obligation to arm you with all the ammo I think you'll need. You'll be going after experts who have been there before, they will have a distinct advantage over you.
Gee, I guess "Eterna" really means a "short lived floor", sounds like double speak to me. I rarely now install lower grade material, but it will, in most cases last at least a decade, before some internal cracking shows up. And then those boards have to be replaced. I warned about this in one of my early (free) strip floor articles, not too many people have read this. We hope to have all the info in this site you will need, but it's been over three years work so far, and I'm not sure I'll ever be done. But I think I'll devote an article on prefinished hardwood floor grading.
As always your Most humble servant, Joseph, the Wood Floor Doctor.
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