How to Build Sofas With Foam on Plywood Bases

Lay out two 18-inch 2-by-4 boards on the working surface with their largest surfaces down. Set them parallel to each other about 17 inches apart. Position two 24-inch 2-by-4 boards on top of them, perpendicular to them so their corners overlap with the largest surfaces touching. Arrange the boards so that they form an 18-by-24-inch rectangular frame.

Drill down through each corner, making two holes but stopping before the drill bit enters the floor, for eight total holes. Set 2-1/2-inch wood screws in each hole and tighten them completely to complete one of the couch leg supports. Repeat to make two more couch leg supports.

Set the three leg supports upright on their longest edges, parallel to each other about two feet apart. Position two 3/4-by-24-by-60-inch plywood boards on top of them, stacked on top of each other. Drill down through the plywood boards and into the leg supports to make six holes in each support. Attach the boards together with 2-1/2-inch wood screws. Further secure the plywood sheets together by screwing in 1-inch wood screws every 12 inches around the edge of the boards, about three inches from the edge.

Follow the same procedure as the leg support construction to make two smaller rectangular frames out of four 16-inch 2-by-4s and four 8-inch 2-by-4s. Set these two frames, which are the arm rests, along the edges of the couch, with one side flush with the end of the plywood sheets and one side flush with the rear of the couch.

Drill four holes up through the plywood sheets and into each arm rest. Attach the arm rests in place with 2-1/2-inch wood screws.

Set two more 3/4-by-24-by-60-inch sheets of plywood on top of one another and screw them together with 1-inch wood screws spaced every 12 inches around the edge, about three inches from the edges. Put screws every 12 inches along the center line of the boards as well.

Hold these joined plywood pieces up against the rear of the couch so they overlap the installed plywood seat and are flush against the rear of the armrests. Drill three holes through the plywood and into each arm rest. Attach the plywood, which is the backrest, to the arm rests with 2-1/2-inch wood screws.

Set 1-inch metal L-brackets every 12 inches along the joint of the backrest and seat plywood boards. Drill 1-inch screws into the holes of the brackets to fully install the backrest.

Cover the seat, backrest and arm rests with foam to the desired depth and comfort level, stapling it in place as necessary. Cover the couch with tightly stretched fabric and staple the fabric in place in the corners of the seat and around the arm rest and backrest. Stretch the fabric under the couch and staple it every four inches in a circle four inches from the edge. Cut off excess fabric with a scissors.