4-seat sofa sofa plans

Parts

Cut list

Kerf 1/8″ included. Every cut runs edge to edge.

Steps

• Tape measure
• Speed square
• Pencil
• Drill/driver
• Clamps
• Safety glasses
• Hearing protection
• Dust mask
• Circular saw and a straight edge (or have the store cut the sheets)
• Two bar clamps at least 36″ long
• A helper for lifting the sides
• Sander, 120 and 180 grit

Underlined words have a short explanation: hover or tap them. All of them are on the glossary page.

1. 1Before you start

   Read every step once, start to finish, before you buy or cut anything. Each step names the parts it uses by letter; the parts list gives their sizes.

   Set up somewhere flat with good light. A pair of sawhorses with a sheet of plywood on top makes a fine work table.

   Wear safety glasses whenever a tool is running, hearing protection for saws, and a dust mask for sanding and for cutting treated wood or sheet goods. Tie back long hair and loose sleeves. Keep children and pets out of the work area.

   • Tip At the store, pick straight boards: hold each one up to your eye and look down its length. Skip boards that bow, twist or have big knots near the ends.
   • Tip Measure twice, cut once. Most mistakes are a misread tape, not a bad cut.

2. 2Cut and label the parts

   Cut every part on the cut list. Cut the longest parts first: if one goes wrong, it can still become a shorter part.

   To mark a cut, hook your tape on the end of the board, make a small V with its point exactly at the measurement, and draw a square line through the point with a speed square. Put an X on the waste side.

   Cut on the waste side of the line, so the blade's kerf (about 1/8″) comes out of the scrap, not your part. Cut sheets with the good face down when using a circular saw: the blade splinters the top face.

   Write each part's letter in pencil on a face that won't show, and stack the parts by letter.

   Sand the faces before assembly while they're flat and easy to reach: 120 grit, then 180.

   ✓ Lay the parts out and count them against the parts list. Measure a few: if one is off by more than 1/16″, recut it now.

   STOP. Let the saw reach full speed before it touches the wood, keep both hands clear of the blade's path, and never reach under a board you're cutting. Support long boards on both sides of the cut so the blade doesn't pinch.

3. 3Cut the leaning back posts

   The back posts (B) lean back 12° so the back reclines. Both ends are cut at 12° so the foot sits flat on the floor and the top is level. The two cuts are parallel, 32 11/16″ apart measured along the edge.

   Near one end of a 2×4, square a pencil line across the face. Put the fence (the thick lip) of a speed square against the edge with its pivot point on that line, and turn the square until the edge lines up with 12° on the DEGREE scale. Draw along the square: that is the first cut.

   Measure 32 11/16″ along the same edge from where the first line meets it, and draw the second angle the same way, sloping the same direction, so the two lines are parallel (the board becomes a long, thin parallelogram).

   Cut on the waste side of each line with a circular saw or miter saw. Use the first post as a pattern to mark the second, so both match.

   • Tip If you have a miter saw, set it to the angle and cut both posts in one setting so they match exactly.

   ✓ Stand each post on its foot on a flat floor: it sits flat with no gap under either corner and leans back on its own line.

   STOP. Clamp the board before cutting; never cut a board you are holding.

4. 4Build the two side frames

   Lay a front post (A) on the floor on its narrow edge, floor end against a straight board. Lay the side rail (C) and the arm rail (D) across it, front ends flush with the front of the post: the side rail's bottom edge 7 5/16″ above the floor, the arm rail's top edge flush with the top of the post (22 1/2″).

   Slide a back post (B) under the back ends of the rails, leaning back, with its foot flat against the same straight board. Line it up so its back edge crosses the bottom edge of the side rail 30 11/16″ from the rail's front end, and the top edge of the arm rail 33 15/16″ from its front end. The arm rail is cut 33 3/16″ long so its back end lines up with the post.

   Spread glue where each rail crosses a post. Drive 4 screws, 3″, at each crossing in a square pattern 1″ in from the edges. Drill 1/8″ pilot holes first.

   Build the second side as a mirror image: the rails go on the inside face, so on a finished piece both sets of rails face each other, and both back posts lean back.

   • Tip A screw in each corner of a square is far stronger than four in a row: it stops the rail from pivoting.
   • Tip Pick the straightest 2×4s for the posts; sight down each one at the store.

   ✓ The two side frames match when stood face to face, both back posts lean the same amount, and the rails are parallel to the floor board.

5. 5Line the arms with plywood

   Each arm panel (E) covers the inside of a side frame. Hold it against the inside faces of the rails, bottom flush with the bottom of the side rail, 1 1/2″ back from the front and the back ends (the front and back rails butt into those gaps).

   Glue and drive 1 5/8″ screws through the panel into both rails every 6″.

   The panel turns the open frame into a stiff box, so the arm cannot rack when someone leans on it, and it is the wall the cushions sit against.

   ✓ Push the top of the back post sideways: the side frame does not change shape.

6. 6Join the sides with the front and back rails

   Stand the side frames up, panels facing in, 97 3/8″ apart between the side rails. A helper holding one side makes this much easier.

   Fit a front rail (G) between the side rails at the front, flush with their fronts and bottoms. Glue the end of the rail, clamp it in place and drive 2 screws, 3″, through the side rail into its end (pilot holes first, 1″ and 4″ from the top edge). Then screw 2 L-brackets into the inside corner, one high and one low.

   Fit the back rail the same way at the back.

   Measure the diagonals across the frame (front left post to back right post, and the other way). Push the long corner until they match, then let it sit.

   ✓ The frame is 103 3/8″ wide, the diagonals match within 1/8″, and all four posts touch the floor.

   STOP. Lift the frame with a helper from here on; it is heavy and awkward.

7. 7Add the ledgers and deck joists

   Screw a ledger (H) along the inside face of the front rail and another along the back rail, between the arm panels, with the ledger top 3 1/2″ below the rail top. On a sofa this long each ledger is two pieces butted end to end. Glue and drive 2 1/2″ screws every 8″.

   Set the 9 deck joists (I) on edge on the ledgers: one tight against each arm panel and the rest every 12″ on center, so one lands under every cushion seam and one under the middle of every cushion. Their tops are flush with the rail tops.

   Drive 2 screws, 3″, through the front and back rails into the end of each joist.

   • Tip Mark the joist positions on both rails with a square before you start so the joists run straight front to back.

   ✓ A straightedge laid across the rails touches every joist: nothing high, nothing low.

8. 8Lay the seat deck

   Drill five or six 1″ holes through each deck piece (J, K), spread out: cushions push air out when someone sits, and the holes let it go.

   Lay the deck on the rails and joists between the arm panels, back edge flush with the back rail. Where two pieces meet, the seam lands on the middle of a joist.

   Drive 1 5/8″ screws every 8″ into the rails and every joist.

   ✓ The deck is flat; stand on it near the middle of each seat and it doesn't flex.

9. 9Build the back

   Fit the top back rail (L) between the back posts, its top front corner level with their tops and its back face flush with their backs, so it leans back 12° with them. Glue the ends and drive 2 screws, 3″, through each post into the rail end (pilot holes first), plus an L-bracket in each inside corner.

   Cut the back stiles (M) like the posts: both ends at 12°, parallel, 15 1/8″ apart along the edge (speed square fence on the edge, pivot on a squared line, turn to 12°).

   Stand a back stile on the deck at each cushion seam (27 11/16″, 51 11/16″, 75 11/16″ from the left outside edge), its back face in line with the back of the posts, leaning back like them: lay a straightedge across from post to post to line it up. Screw through the top rail into each stile, and toe-screw its foot into the deck.

   Lay the frame on its front on a blanket. Fit the back panel pieces (N, O) over the back, edges flush with the outsides and the top, bottom edge on the back edge of the deck; seams land on a stile. Glue and drive 1 5/8″ screws every 8″ into the posts, stiles and top rail.

   The back cushions rest against this panel and lean back 12° with it, the way a bought sofa does.

   ✓ Stand it up and push the top of the back from the front: it doesn't lean or creak.

10. 10Cap the arms

    Round over every top edge of the arm caps (F) with 120-grit paper or a router: arms get touched more than anything else.

    The back post leans, so the back end of each cap is cut at a 12° bevel (tilted through the thickness) to sit tight against it. Set a circular saw's bevel scale or a miter saw's bevel to 12°, cut a scrap first and test it against the post, then cut the cap so its top face is 30 5/8″ long and its bottom face is the shorter one.

    Lay a cap on each arm, back end tight against the back post, outer edge flush with the outside of the post. It overhangs the arm panel on the inside by about 1 13/16″.

    Drill and drive 3 screws, 3″, down into the front post and 3 into the arm rail. Fill the screw holes with wood filler and sand flush.

    ✓ Press down hard on the front end of each arm: no movement.

11. 11Order the cushions and test

    Order 4 seat cushions 24″ wide × 30 1/2″ deep × 5″ thick, and 4 back cushions 24″ wide × 15″ tall × 5″ thick. Ask for high-density foam (1.8 lb or more) wrapped in batting, with zip covers.

    Measure your own frame before you order: the seat cushions should fill the space between the arm panels with no more than 1/4″ left over.

    Before anyone uses the sofa, sit down slowly, then rock gently side to side and front to back. Nothing should creak, shift or rack. If a joint moves, add glue and a screw there before going further.

    • Tip Cushion makers quote by exact size; a cushion 1/4″ too small looks sloppy, 1/2″ too big bulges. Send them the frame's measured inside size.

    ✓ No creaks, the deck doesn't flex under you, and the frame doesn't move when you lean into a back corner.

12. 12Finish

    Ease every sharp edge and corner with 120-grit sandpaper so nobody gets a splinter.

    Sand all over with 180 grit, always along the grain (the direction the wood fibres run). Scratches across the grain show through stain.

    Wipe off the dust with a barely damp rag and let it dry.

    Paint, stain or a clear coat (water-based polyurethane is the easiest). Apply thin coats with the grain, let each dry fully, and sand lightly with 220 grit between coats.

    Let it dry for the time on the can before using it.

    • Tip Try your finish on a scrap of the same wood first: stain looks different on every board.