We've decided to have installed 3/4" hardwood plank flooring (3" width) in our dining room. The subfloor is 3/4" T&G plywood over standard dimensional lumber joists and is accessible from below. In talking with dealers/installers, I've been told a couple times that nailed-down hardwood planks have to be installed perpendicular to the underlying joists in order to insure a strong flat installation. Is this accurate? Our room is roughly 16x10, with one corner angled off a fireplace hearth. The layout of our room is such that laying the planks along the long wall, which runs parallel to the joists would be much more esthetically pleasing. I've laid out a 3x3' sample in both directions. Running the planks along the short side is not visually pleasing, and is coincidentally perpendicular to the flow of traffic. To get to my question: Is there a method of installation that would accommodate laying out the planks parallel to the joists? I hate to think that this project could be scrapped because of this technicality. We've got our hearts set on a solid plank floor system as opposed to a floating laminated or engineered system. Thanks for any help anyone can provide.

Running the wood flooring perpendicular to the floor joists is the proper way to do it. It is correct the flooring will not stay as flat nor will it be secure if it is running parallel to the joists.

There is one good alternative though that will work:

You said the floor joists are accessible from beneath. Go underneath and install 2 x 6 blocking at 16” on center between the floor joists. The 2 x 6s should be approx. 14.5” long to fit securely between joists spaced at 16” on center. The 2 x 6s should be placed with their 1 ½” side up tight against the plywood sub floor. This will effectively give you the same support as the joists for nailing the new plank flooring and you can turn the planks any direction you like.