How Can I Change a Square Hall Into an Archway?

Use a knockdown knife to cut away the drywall at the top of the existing doorway to expose the framing. Determine the size and shape of the arch and draw the guide on a piece of cardboard. Hold the piece of cardboard up to the top of the hallway entry to ensure the cut of the arch will fit correctly and won't reach up to the ceiling. Outline the template on two pieces of 1/2" plywood.

Use a circular saw to cut the patterns from the plywood. Cut a 2-by-4-inch block of wood into 2-1/2-inch wide pieces. Nail two of the blocks to the door framework with a nail gun, centering them so that the plywood cutouts will rest flush against the existing framing. Nail the plywood arches into the wood blocks. Move the remaining 2-by-4 blocks approximately 6 inches apart at the bottom of the plywood frame, between the two pieces of plywood and nailing each in as it is placed.

Cut a strip of 1/8-inch hardboard to fit the length and width of the archway. Nail the strip to the arch blocks, following the curve at the base of the plywood using 1-5/8-inch drywall screws, so that the finishing drywall does not crimp or collapse into the space between the 2-by-4 blocks. Cut a strip of 1/4-inch pliable drywall to fit the length and width of the archway. Nail it to the hardboard.

Apply flexible corner bead tightly to the drywall and secure with a nail gun. Use a putty knife to spread joint compound in thin layers, letting each apply before applying another, until the corner bead is hidden. Sand and paint the finished arched entryway.