Originally Posted by
Lit Jones
I would not lay it perpendicular to the old floor, because you really do want the floor to be perpendicular to the floor joists. Even if you think the existing floor is dead flat, the floor tends to move 1 joist at a time when you walk across it, and you want that movement to be resisted by the grain direction of the floor.
To picture what I am saying, think about a two pieces of t/g flooring fit together. If you try to flex this assembly across the grain, it will easily flex at the joint. If you try to flex it the other way, it will resist.