Hello all! First post and I want to first say thank you for the wealth of invaluable information on these forums. I'm about to embark on my first hardwood flooring project and I'm quite sure I would have ended up with major problems later had I not found this site.

OK, here's my situation. 1300 sq. ft. home, with the original section built in 1928 two sections added later. (Interesting history - it started as the servants' quarters to a plantation style house across the street, and was moved to it's current location at some point).

I am installing roughly 800 sq. ft. of prefinished nail-down strand bamboo strip flooring (9/16" x 3 3/4" x 72") from Cali Bamboo ("Fossilized" Series). I believe it is very similar to Teragren's "Synergy" Series. I just received the flooring and am very impressed with the apparent quality. I took a chance ordering site-unseen, but I think I made a good decision. This is the hard stuff (Jarka = 3000) and I'll be using 18 gage cleats rather than staples since I am over a crawlspace.

Please bear with me while I describe the intricacies of the layout...

Oldest section:
The great room, (short) hallway and master bedroom all reside in the original section. This area has what I believe to be 3 1/4" T&G strip yellow pine subflooring, laid across 24" OC joists. The joists run front-to-back in the long direction here, which is East-West. There is NO OTHER FLOORING in this entire section. The face of the subfloor has been sanded/stained and functions as the walking surface. As you can imagine, the floor can get quite cold and even has some minor drafts in a few areas. The face has some significant shrinkage and splitting, and minor ridging where the faces meet, but the bottom actually looks pretty good, and overall it seems in decent condition. It's fairly noisy right now, so I plan to use drywall screws at the joists to minimize creaking/squeaking. I will then be feathering 30# felt to shim minor low spots here and there, and there are two not-so-minor low spots (1/2" in 8') that I'll be shimming with layers of 1/4" plywood and 30# felt.

2nd Section:
This part of the house was added later, but I don't know when. It contains the 2nd bedroom, kitchen and laundry room. This section has what I believe to be 1" x 6" Yellow Pine subfloor planks laid diagonally across the joists, which run North-South. On top of this, in the 2nd bedroom, lies 3 1/4" strip wood flooring of unknown species stained to match the flooring (i.e. subfloor) in the oldest section of the house. I think it's probably Maple. The surface of this floor meets up at the same level as the surface of the "subfloor" in the oldest section, with a threshold piece in the doorway. This floor runs the same direction as the older floor (North-South).

Front & Garage Section:
The entryway + dining area in the front, and the garage to the side, are all slab-poured. The garage has since been enclosed and finished minus the floor, which has plywood of unknown thickness overlaid on the concrete. I will eventually cover this garage room with the bamboo, but I'm putting a bathroom and closet in there first so the flooring in the garage room will come much later. The front entryway & dining area have the same flooring (Maple?) as in the 2nd bedroom, floated on (2) 3/4" layers of plywood. I will be tearing all of this out and staining the concrete below, which will leave this section appx. 2" lower than the face of the current floor (subfloor) in the oldest section of the house. Part of the threshold between old/front section has a wall, but there will be a 10' span where I will have to use stair nosing to accommodate the height difference, which will eventually be either 2 9/16" or 2 15/16", depending on your answers to my questions.

OK - now that that's out of the way, here are my questions:

1. After I shim the low spots, can I lay the bamboo directly over the existing flooring or do I have to install a 3/8" plywood underlayment first? I'd sure like to avoid laying the plywood if possible. If I can skip the plywood, I would go perpendicular to the existing flooring/subfloor, which is not really a problem as far as aesthetics go. Everything is fairly small and square-shaped so there are no long runs, and this would put the new flooring lengthwise down the hallway. It would, however, also put the flooring parallel to the joists in the oldest section of the house, with only the old subfloor underneath it. It would also put the flooring perpendicular to the 10' run of stair nosing, and I'm not sure how I would go about installing up to or from the nosing.

2. If I do have to put the 3/8" plywood down first, what grade should I use (is BC alright?) and do I have to lay it diagonally or can I just lay it with the grain perpendicular to the subfloor? This would make the 2nd bedroom 1" x 6" diagonal subfloor + (Maple?) hardwood + 3/8" plywood + bamboo floor... any issues with that configuration? If I put plywood down I'll probably lay the flooring East-West to go parallel with the stair-nosing (which would be probably the most prominent feature). I'd use a tongue strip and start the flooring there which would be simpler than the alternative, perpendicular layout.

Thanks in advance for any advise you can give me!

Josh

Putting myself in your shoes I would install 3/8 or 1/2 BC plywood underlayment. Lay it crossing the joist and leaving an 1/8" gap between each sheet.

How thick is that 3 1/4" T&G pine subfloor? Your joist being 24" OC I suspect the bamboo will need to be laid perpendicular or diagonally from the joist.

Thanks Jerry. I'll go with the plywood then, and lay the bamboo perpendicular to the joists. It will be more work up front, but I think it will actually simplify the install. I need to re-measure one door, but if I have enough clearance I'll use 1/2" instead of 3/8" since it's not that much more money or work.

So I'll start the install at the 10' stair nosing span. If I glue down the stair nosing with PL400 do I still need to face-nail it? I'll use a spline to work away from the nosing.

Yes, facenail.