How to Build Rounded Arches in Doorways

Measure the thickness of the wall at the opening of the doorway with a tape measure. Subtract from this measurement the thickness of the plywood that will be used to frame each side of the arch and the drywall used to cover the framework on each side. Note that two thicknesses of ½-inch plywood and two thicknesses of ½ inch drywall would equal 2 inches that you need to subtract from the wall thickness. Note that the remainder determines the width of the framing lumber that will be sandwiched between the plywood.

Measure the across the width of a length of 2-by-4 lumber and make a mark at the measurement determined previously. Rip the lumber to width on a table saw or with a circular saw. Rip three lengths of 8-foot long lumber to frame the average arch.

Measure the width the doorway where the arch will be constructed. Cut a piece of the ripped lumber to this length with a circular saw. Nail the piece flat to the upper horizontal side of the doorway with 16D nails.

Cut two pieces of the ripped lumber to a length that is equal to one-third to one-fourth the width of the arch, depending on the curve of the arch you desire. Note that these pieces will serve as the vertical frame of the arch. Nail the pieces to the vertical sides of the doorway directly below each end of the top horizontal piece with 16D nails.

Cut two rectangular pieces of ½-inch plywood with a circular saw to a length and width that equals the lengths of the horizontal and vertical pieces of the arch framework. Lay the pieces flat across two sawhorses. Clamp the plywood together with C-clamps. Draw an ellipse on the face of the top sheet of plywood to your desired arch shape. Cut through both pieces of plywood on the line with a jig saw. Remove the C-clamps.

Lift one of the cut pieces of plywood to the framework in the doorway installed earlier. Nail through the plywood and into the horizontal and vertical pieces secured to the doorway with 8D nails.

Use the remaining lengths of ripped lumber to construct spacers to fit between the two pieces of plywood. Cut the pieces to length and place them on end at five to six inch intervals along the entire length of the arch on the piece of cut plywood not installed yet. Clamp the pieces to the plywood with C-clamps and nail them in place with 8D nails. Remove the C-clamps.

Lift the plywood with the spacers attached to the doorway, ensuring that the spacers are facing inward and the edges of the plywood lay flush on the horizontal and vertical pieces installed in the doorway. Nail the plywood in place with 8D nails. Secure the first piece of plywood installed to the opposite side of the spacers by nailing through the outside of the plywood and into the spacers with 8D nails.

Cover the vertical sides and the horizontal underside of the plywood arch with 1/2 inch thick drywall and finish it to match the surrounding walls.