How to Make Built-In Benches for Your Deck
Benches built parallel to the joists can be any length. You can build both types on the same deck. It's easiest to frame built-in benches before the decking goes on. Bench seats should be about 18 inches above the decking and 15-30 inches deep. Built-in perimeter benches help define the edge of a deck in addition to increasing the seating.