Hi to everybody,
there is an existing 3/4" plywood subfloor. I would like to be able to run bamboo planks, length 38 width 3-3/4 and Height 5/8, parallel with the flooring joists.

Do I need an additional layer of plywood underlayment? If yes, what kind and thickness?

Existing floor plan available here:
http://picasaweb.google.com/mjlabas/Home/photo#5086014790185371026

Thank you.
-m.

Yes.

½"

Thanks.
However, I am starting to have more and more doubts about layout.

My reason to have it parallel to joists:
1) Parallel to direction of light (there are sources recommending that)
2) Parallel to direction of traffic (my personal opinion, should look better)
3) My initial visualization, what it should look better, especially in narrow hallway
(unless I decide to change direction for the hallway, running entire room perpendicular to joists).

Reasons to have it perpendicular:
1) Most sources recommend starting from the longest outside wall.
2) Suppose to make room visually larger.
3) Don’t need to spend extra time and $$$ for underlayment.
4) Perpendicular to entry itself (recommendation from Hardwood Flooring Layout--Which Direction To Install)