i posted about the glued down existing floor and appreciate all the responses. after starting to pull up the old floor, i reassessed and determined that if i have to replace the subfloor that is damaged in the removal, i might as well leave the existing hardwood in place and built up the areas that are now carpeted, then put the new 3/4" BR111 3" strips over it.

my question now is, since my wife would like to run the boards parallel to the joists, will this new thickness give me enough support? the existing subfloor is 23/32 (3/4") OSB and the existing subfloor is 3/8" oak. i found 11/32 (3/8") plywood and OSB at home depot. which would be best?

the final thickness of subfloor and underlayment will be approx. 1 1/8". i got don bollinger's book & video (great stuff!), but he doesn't talk about an overall (subfloor + underlayment) thickness for installation parallel to joists. the existing hardwood is perpendicular to the joists and i would lay the underlayment the same.

appreciate all responses. thanks in advance,

Use the 3/8" CDX plywood over your OSB subfloor. Staple or screw securely in a grid pattern 6" around the perimeter and 8" oc in the field. This will allow you to run the flooring parallel to the joists. I recommend you locate any high areas of the subfloor first and sand them flat before installing your CDX underlayment.

gary,

thanks for the reply and for the info on ken's sticky. that's very helpful and i'll plan on the 11/32 ply. checking home depot, though, i found that the ply is rated "BC Sanded" and doesn't designate "CDX". is this suitable?

also, i took a piece of the existing 3/8" oak to compare the thickness and in fact it is about 1/32 thicker than the plywood, so there will be a slight height difference. will the 15" felt layed across this joint even things out or perhaps can i do my 4" felt overlap from the oak to the ply to shim it somewhat.

another option may be to use felt paper as shims or lay 2 layers of felt on the ply (maybe one under and one over) with only on layer on the oak to bring the ply up? what do you think of that?

i suppose i could also sand the oak with an edger if i can rent one, but would like to avoid that. if i have to, would it be best to sand all the oak floor down, or just the part that will abut the ply to taper it down to the same level? there will be a total of 4 rooms coming off the oak entryway and hallway that will require this.

once again, thanks for this invaluable resource.

Where the new plywood underlayment meets your existing oak floors, simply "fur" up the underlayment at the joint the 1/32" you need to be flush. Sanding would be another option; just sand the seam. CDX refers to the grade. Can't get much cheaper than CDX. The C is the grade for one side, the D is the grade for the backside, and the x stands for exterior glue, which means it can get rained on a little before falling apart. The BC your looking at will cost more and isn't needed. Try to locate the CDX. If you do use the BC, which is fine, try to get it with an Exterior rating. If not, don't worry, it will be fine.

thanks a million! will keep you posted on progress. the wood arrives on tuesday, so after acclimation it's "slide-slam-bam-bam-bam" (in marco's words. actually it'll be more like "by the time i'm done i'll good").

Gary (and everyone else that's helped),

Haven't posted for a while, but got the upstairs finished (approx. 1,200 sf and all went well. Moving to downstairs now where I have to put underlayment on parts of it to bring it level with the exisiting oak floor.

I know you indicated screws at 6"oc on perimeter and 8"oc in field, but am afraid that may result in hitting a lot of nails/screws when stapling down the planks, resulting in rejected staples and delays in prying them out.

Would it be okay to glue down the underlayment with the thought that the staples for the planks will solidify the attachment as they are long enough to go through the tongue, underlayment and sublfoor (and somewhat into the joists if I hit them)?

If so, what type of glue should I use? If not, I am thinking of using 2" ringshank underlayment nails. I know you recommend screws, but the best ones I could find were square drive 1 5/8". They would hold the underlayment to the subfloor, but wouldn't go very far into the joists. Are drywall or decking screws acceptable?

I tried searching prior messages and stickies, but couldn't find answers to these particular questions.

Once again THANKS for all the info. Things wouldn't be going so well without it!

gluing will work just lord help you if you ever have to remove they will come out as one. Shouldnt be a real problem in hitting nails anyway.

Don't worry about hitting all the joist when you do this. Make sure the "first" layer is nailed good to the joist, then cross-lay and stagger the 2nd layer. I use yellow wood glue and screws about 6-8" apart.

You want both layers to become one monolithic subfloor, no squeaking that way.

I do alot of plywood over subfloor work because of people wanting to run flooring parallel with joists, crappy subfloors, P. board subfloors, etc. While gluing seems like a good idea, and I suppose it's ok, I like to be able to repair a floor down the road if needed. If you glue that underlayment to the subfloor, you'll be ripping up chunks of subfloor if you ever needed to remove a section of that underlayment. My approach is top use lots of staples. I use a 16 guage, 1/2" crown stapler from Senco. It's fast, the staples are inexpensive and they suck the underlayment down to the subfloor and hold very well, better than nails. Of course screws hold better but that is slow, expensive and not much better. Anyway, if you can rent a construction stapler for the day, you'll be surprised at how good a job it does.

I'm not disagreeing with ya Mr.Gary. For some reason I tend to overkill everything I do, just my nature. I look at this way, cheap insurance. I use a gallon jug and just run beads and lay the plywood down in it.

That 1/2" crown stapler is what I need to change to, screwing is too slow.

Ya' ll have a great weekend.