How to Install an Arched Doorway

Cut away at the drywall surrounding the doorway with a utility knife until the framing is exposed.

Measure the space between the sides of the door frame to determine your arch dimensions.

Tie a piece of string, cut to half of the width of the door, to a pin and insert the pin into the middle of the cardboard. Tie the other end of the string to a pencil. Pull the string until it is stretched all the way and begin drawing a circle on the cardboard using the pencil. Cut the circle out and divide it into two equal parts. This forms your cardboard arches.

Tape one of the cardboard arches to the bottom of the top frame to determine that there is enough headroom under the arch.

Trace the outline of the arch on the 1/2-inch plywood pieces and cut them out to get two plywood arches.

Cut 2-by-3-inch lumber into three pieces to support the arch along the sides and top. The size of these pieces will differ based on the height and width of the arch.

Position the lumber pieces, two on each side of the frame and one at the top and nail them into place using 2-inch nails.

Place the arches on either side of the lumber pieces and nail them into place using 2-inch nails. Make sure that the circumferences of both arches are flush.

Saw 2 1/2-inch lumber blocks to meet the shape of the arch and screw them between the plywood pieces using drywall screws. These blocks prevent the arch frame from collapsing inward by providing interior support. The number of blocks will vary depending on the size of the arch.

Cut a piece of hardboard to the circumference of the arch, extending down to the base of the frame assembly. Trim it to the thickness of the space between the plywood pieces. Bend it into shape along the archway and nail it into the lumber blocks using 2-inch nails, spaced 4 inches apart.

Cut two pieces of drywall to roughly resemble the dimensions of the plywood arches and cover either side of the archway with them. Trim off any excess with a utility knife.

Trim a strip of drywall to the thickness of the wall and the inside length of the arch, enough to cover the frame assembly, and let it soak in water for an hour or until it can bend to the shape of the arch.

Position the drywall strip below the curve of the arch and screw it into the hardboard using drywall screws.

Staple flexible plastic corner beads into both edges of the archway. Make sure the corner beads are fastened tight against the drywall to give the arch its shape.

Mix joint compound and apply it to the entire archway, covering the corner beads. Apply a second layer if required.

Sand the arch with sandpaper and paint when it has dried.