Create a stronger beam by fastening three 2x10s together.
The beam for this deck is made of three 2x10s.
Many older decks were built using massive timbers -- 4x6s or 4x8s -- for beams. Some builders still do it that way; using a one-piece beam can save time. But large timbers are heavy and hard to handle. They often warp beyond remedy, and they almost surely will crack over the years. Fastening multiple pieces of 2x lumber together actually creates a beam that is stronger than a single piece of 4x or 6x lumber.
If a deck design is complicated, it often makes sense to build a beam that is about 1 foot too long and cut it to length after the framing is in place. The beams for this deck can be cut to exact length before they are installed.
About 2 hours to build a 14-foot-long beam made of three 2x10s with plywood spacers
Tape measure, circular saw, drill, long bit, hammer, clamps, adjustable or socket wrench
Measuring and cutting a board, fastening with screws and bolts
Set up two or three stable sawhorses and lay the beam pieces on them
Lumber for the beam pieces (2x10s in this case), pressure-treated plywood, 1 1/4-inch deck screws, 3-inch deck screws, 3/8 x 6-inch carriage bolts with nuts and washers
Low decks might not provide enough vertical space for joists attached to the top of a beam. The solution is a flush beam, which is essentially a header that has been doubled for strength. Cut two headers (the boards that will be perpendicular to the joists) and mark lines on them indicating where the joists will go. Fasten them to the posts so they are level. Double up the headers to make them flush beams. Drive a pair of nails or screws every 16 inches to bind the pieces together firmly. The second piece is 1-1/2 inches longer than the header on each end to accommodate rim joists on both sides of the frame.