How to Build Exterior Arches

Constructing the Arc

• 1

  Measure the width of the area where the arch is to be constructed, using a tape measure. Cut two sheets of 1/2-inch-thick plywood as long as this length and as wide as half this length, using a circular saw. Tie a piece of string around a pencil. Cut the string as long as half the width you measured.

• 2

  Pin the string to the middle of one of the long sides of one plywood sheet using a thumbtack. Draw out an arc on the plywood sheet using the pencil. Re-pin the string to the middle of the long edge, leaving 2 inches of string trailing loose behind the thumbtack. Draw out a second arc. Repeat both arc drawings on the second plywood sheet. Cut along each arc line with the jigsaw to produce two plywood arcs.

• 3

  Measure the length of the outer curve on one of the arcs. Divide this length by six to find the length of wood pieces required to build the arch. Cut 24 pieces of 2-by-4 lumber as long as the length you just calculated, using the circular saw. Place six pieces on each arc, forming a basic arc with squared-off sides. Apply wood glue between the 2-by-4 pieces.

• 4

  Screw the pieces to the arc using countersunk 3-inch-long screws. Wait 30 minutes for the wood glue to set. Clamp the arcs to a solid surface using G-clamps. Cut along the curved edges of both arcs using a jigsaw, to remove the excess wood on the 2-by-4s.

• 5

  Glue and screw the six more 2-by-4 pieces to the 2-by-4 pieces you just cut. Cut the excess from these pieces also. Sand down the curves on the arcs using medium-grit sandpaper to produce smooth arced wood pieces. Measure the length of the area where the arch is to stand. Cut nine pieces of 1-by-2 lumber to this length.

• 6

  Screw one 1-by-2 piece to the bottom end of either side of the arcs using two countersunk 2-inch-long screws per joint, to join the arcs together. Screw one 1-by-2 piece to the top of both arcs using two countersunk 2-inch-long screws per joint. Screw two 1-by-2 pieces to both sides of the arcs, equidistant between the top and bottom pieces.

Building the Arch

• 7

  Cut four pieces of 2-by-4 lumber 91 inches long using the circular saw. Cut six pieces of 2-by-4 lumber to the length of the arch area minus 8 inches. Lay two of the 91-inch-long pieces on the ground with a 4-inch-wide face against the ground. Measure 12 inches along both pieces, using the tape measure. Mark these points with a pencil.

• 8

  Screw one arch-length piece in between the 91-inch-long pieces at the marked points, using two countersunk 6-inch-long screws per piece. Screw a second 2-by-4 piece between the two 91-inch-long pieces at the top of the pieces, using two countersunk 6-inch-long pieces per joint. Screw a third arch-long piece in the middle of the distance between the first two pieces using two countersunk 6-inch-long screws per joint.

• 9

  Cut a sheet of trellis 84 inches long and as wide as the length of the arch area. Screw the trellis to the 91-inch-long pieces and the arch-long support pieces using countersunk 2-inch-long screws. Repeat this process to form a second side frame for your arch with 12-inch-long foundation support posts that can be stuck into the ground to support the arch.

• 10

  Lay the arc on the ground so one of the curves is flat against the ground. Stand the side support frames on the ground so the top of the support frames is touching the flat bottom faces of the arcs. Screw the support frames to the arcs using lag bolts and mounting plates. Varnish the arch using exterior-grade varnish and a paintbrush.