After you choose the size deck you want, you now need to think about the frame; the foundation to you deck. Like a house and deck needs a foundation as well. Different sized decks require a bigger foundation, so one you figure out the size deck you want the framing is not hard to figure out as well.
As in your house, deep in the ceiling where no one can see lies the the joists; these wood boards are lined up holding your entire house together. Well your going to need to recreate that joist hanging system for your deck too. This ensures the deck is safe for all as joists maintain the shape and strength of the deck.
Joists generally run perpendicular to the house and are suspended between the ledger board attached to the house and a beam or between 2 self supporting beams. Joist hangers are used to attach the ends of joists to the face of a beam or a ledger board. Joists are installed parallel to each other for ease of construction and to distribute weight evenly for structural integrity.
The term they use for properly laying a joist is “On Center”; which is the center to center measurement from one joist to the next. Most decks use 16″ on center spacing for joists.
NOTE: Most decking is not strong enough to support longer spans than 16″.
As wood is pretty cheap and couple extra boards will not hurt a thing, most builders prefer to reduce joist spacing to 12″ on center to strengthen the deck frame. The materials used for joists sizes are most often 2×6, 2×8, 2 x10 or 2×12. They are the most widely used, economical and easiest to find/purchase. The larger the joist size the longer the allowable joist span.
When installing your joists you should carefully examine the board for defects. If you identify a crown in the board you should always install it upwards. The crown will eventually settle after completing construction and should stiffen in the proper position after drying.
Another defect to look out for would be a large knot at one side of the joist. If you intend to use a joist with a knot like this be sure that it is at the top side after installation. The topside of a joist is always under compression and the bottom is always under tension. If you have a knot on the bottom of a joist it will not hold under tension and it will fail.
If you notice your board has a twist in it after attaching it to the ledger, you should try to straighten it before nailing on the header. You want all your joists as perpendicular as possible.
