How to Build a Hallway Arch

Cut the drywall arch surrounding your hallway entrance until the framing is exposed with a utility knife.

Measure the width of the entrance with a measuring tape.

Draw the arch of your choice on a piece of cardboard freehand or using a compass. If none of these work, you can push a pin through the center of the cardboard and tie a string around it. Tie a pencil to the other end of the string, pull it and start drawing a circle. If you keep the string stretched while drawing, you should get a perfect circle.

Cut out the circle from the cardboard and split it into two equal semi-circles.

Tape one of the cardboard arches to the top frame to make sure that you have enough headroom underneath.

Trace the outline of the cardboard arch onto two pieces of 1/2-inch plywood to get two plywood arches.

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

Cut two pieces of drywall to the size of the plywood arches, and screw them into both the arches using drywall screws, covering the plywood completely.

Cut the wooden blocks to the shape and thickness of the arch. Screw them in between the plywood pieces using drywall screws, making sure they run along the curve of the arch.

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

Soak a piece of drywall as thick as the archway in water until it can bend.

Position the drywall strip directly underneath the hardboard and nail it into the hardboard using 2-inch nails. Make sure to bend the drywall strip to the shape of the arch as you are nailing it into place.

Apply corner beads to the edges of the arch, stapling them into place. They are flexible so you can bend them and fix them tightly to the drywall.

Mix joint compound and apply over the corner beads.

Sand the arch and paint it when dry.