How to Build a Room Arch

Cut away the drywall using a utility knife until the framing around the sides and top is exposed.

Tie a pin to one end of the string and a pencil to the other end. Push the pin through the center of the cardboard piece. Pull the string away from the center of the cardboard until it is fully stretched, and draw a circle on the cardboard.

Cut out the circle using scissors and divide it into two equal parts.

Tape one of the cardboard arches to the bottom of the top frame to determine if there is enough space underneath.

Trace the outline of the cardboard arches onto two pieces of 1/2-inch plywood and cut them out to get two plywood arches of the same dimensions.

Position the plywood arches on either side of the top frame and nail them into the frame using 2-inch nails.

Cut two pieces of drywall that resemble the size and shape of the arches. Place the drywall over both the plywood pieces and secure them using drywall screws. Trim off excess drywall with the utility knife.

Shape the lumber blocks so that they are as thick as the wall and run along the shape of the arch smoothly.

Screw the lumber blocks in between the plywood pieces using drywall screws.

Cut a strip of hardboard as thick as the wall and nail it into the wooden blocks using 2-inch nails, bending it into the curve of the arch as you go along.

Soak a piece of drywall the same thickness as the arch in water completely until it becomes flexible enough to bend into the shape of the arch.

Position the drywall strip directly underneath the hardboard and nail it into the hardboard using 2-inch nails, spaced four inches apart.

Apply flexible corner beads to the edges of the arch. Make sure the beads are pressed tightly against the drywall, and secure them with a stapler.

Mix joint compound and apply two layers over the corner beads to cover them completely.

Sand the arch and paint it when it has dried.