Your deck board crown should face up. The deck’s wood joists determine the level of the deck floor. However, since the joist boards are not always perfectly straight, you could still end up with a wavy floor. If a board has a curve to it, the raised side or outer curve is known as the crown. You can determine where the crown is by holding one end of the board and letting the other end remain on the ground. Turn the board so the wide side is horizontal to the ground. Then, bring the end of the board you’re holding up to eye level and look down the board. The board will likely curve to the left, or curve to the right. For a left-hand curve, mark an X on the edge of the board where that curve is located. For the right-hand curve, do the same. These Xs represent the crowns of the boards.
When installing the joists, make sure the crowns (Xs) faces up. With a raised crown facing up, the board will tend to flatten out over time rather than sag. Use metal joist hangers at ledgers and toenail them to the wooden beam using galvanized nails. The spacing between the joists should conform to your area’s building code requirement for the size of deck you are building and the length of the joists you are using. Your joise spacing will also be reliant on the plywood width and the width of the Econodek™ waterproof vinyl deck flooring you are using.