How to Add Double-Duty Built-In Benches to Your Deck

Plan Materials and Layout

First, choose a design and build it from the same lumber as your decking and railings. Otherwise, it will stick out as a displaced design element.

If your built-ins are perpendicular to the joists, the joist spacing will affect the length. 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. For continuous seating, cut enough supports to install one every 4-5 feet. Most building codes permit perimeter seating without a railing on ground-level decks; on an elevated deck leave enough space for a railing behind the seating.

Installation

Mark the locations of the 2x10 legs on the joists. Keep the outer edges of all legs the same distance from the edge of the deck. Cut the legs to length, predrill them for three lag screws or bolts, and fasten them to the joists. Install blocking between the joists adjacent to the legs. Cut the seat rails to the width of the seat and screw them to the legs. Attach a cleat to the outside of each leg as a nailing surface for the decking.

Attach Legs, Blocking, and Seat Rails

Mark the locations for the 2x10 legs on the joist. Attach the legs to the joists with lag screws or bolts through predrilled holes, and attach blocking between the joists to keep the seat from rocking. Cut the seat rails to length—about 16 inches for a bench seat that is 19 inches deep—and screw them to both seat legs.

Install Cleats and Slats

Attach cleats to both sides of the legs to provide a nailing surface for the ends of the decking. You can install the seat slats before or after the decking. But if your slats will overhang the seat rails by more than 6 inches, install the decking first so you won't bump your head against the seats while driving the decking screws.

Determine Height

You can build a bench on posts that extend through the deck like these 4x6s. Instead of cutting the posts flush with the beam, leave them long until the joists are in place. Then you can determine the height of the posts above the deck surface and trim them. You can build a bench shorter than the post spacing by supporting one end on a through-post and the other end on a short piece of post bolted to the beam and joist. If you are building this kind of bench on an elevated deck, make sure the deck overhang is sufficient to build a railing behind the bench.

Install Seat Rails and Cleats

Cut the 2x6 seat rails to the width of the seat and screw one to the outside face of each post. Install cleats on the posts with their top edges flush with the tops of the joists to provide a nailing surface for the decking.

Install Seat Slats

Clamp a 2x4 to each seat rail as an overhang guide. Align the end and edge of the first 2x2 seat slat and screw it to one seat rail. Square the slat to the rails and attach it at the other end. As you screw down the remaining seat slats, space them with pieces of 1/2-inch plywood. If your slats are straight you won't have to square each one.