Because the face of the top board on the stack is exposed to the open air, it may tend to loose more moisture and warp upward. To prevent this it is best to place bricks or weights on the top of it. If you plan to build a piece for inside your home, a good place to store your lumber is in the same room. Behind a shelf or under a couch is an excellent place to let the lumber acclimate to your house's climate. Lumber and furniture placed too close to a fireplace, radiator, or other heat source may dry out and crack.
Plywood is also susceptible to warping.
It should be stored on its end against a wall. All rights reserved.