How to Construct an Arched Window Opening in a Wall

Lay a 4-by-8-foot sheet of 1/2-inch plywood or OSB on the subfloor or a similar large work area. Use the full plywood or OSB panel, oriented vertically, if your plans call for a wall 8 feet high.

Consult the building plans for framing specifications and the height of the doorway nearest the arched window opening. For example, the plans may call for an adjacent 4-by-8 panel containing a door opening, with the door and window panels containing a shared sill plate and a shared double header. If so, lay a door panel adjacent to the panel that will contain the arched window opening.

Clamp together three pieces of 8-foot-long 2-by-4s. Mark the positions of the end studs and intervening studs with a carpenter’s pencil and a speed square according to the plans. Mark the positions of two jack studs, to run from the sole plate to the arched window header, 24 inches apart. Mark the positions for two king studs, to run full length between the top and sole plates, to flank the jack studs, 25 1/2 inches apart.

Unclamp the 2-by-4s. Facenail two of the 2-by-4s together with 6d nails to serve as a doubled top plate. Lay them in position across the top of the adjoining panels. Lay the remaining 2-by-4 across the bottom of the panels to serve as a sole plate.

Measure, mark and cut, out of 2-by-4 lumber, on a chop saw, studs that are 7 feet, 9 inches long. Create one stud for each end of the adjoining panels, as well as two to flank the window as king studs and one to flank the door header. Lay the studs between the plates. Nail through the plates into the studs with 16d nails.

Mark the king studs and the panel between them with a straight line representing the door height, taken from the plans. Make a small “X” on this line midway between the king studs. Measure down 16 1/2 inches, make a small X on this spot and circle it. Fashion a trammel -- a scribe to mark a curved shape -- out of a 1-by-2 board 20 inches long, drilling a hole the thickness of a pencil, centered and 1/2 inch from one end. Mark a spot for a nail pivot 16 1/2 inches away, at the other end.

Nail through the trammel’s pivot mark and into the circled “X” on the panel. Swing the pencil to scribe the arched window top from one king stud to the other. Measure, mark and cut 2-by-4s to create jack studs running from the sole plate to intersect the arched line. Facenail the jack studs to the king studs with 6d nails.

Mark the jack studs 33 inches up from the sill plate. Measure, mark and cut a window sill plate 24 inches long and toenail it between the jack studs.

Trace the outline of the jack studs and window sill plate on the wall panel. Lift the framing out of the way. Lay the panel on cinder blocks and cut out the arched window opening by drilling starter holes in each corner of the outline. Cut out the arch, the straight sides and the straight bottom of the window with a jigsaw.

Cut a 2-by-10 board 24 inches long with a circular saw. Lay the board on your work surface and lay the cutout arch on top of the board. Trace the arch outline on the board so that the arch aligns with the bottom of the board. If you’ve centered the arch on the 2-by-10, it should leave 1 1/2 inches uncut on either side of the arch; these straight edges rest on top of the jack studs. Cut the 2-by-10 along the traced line with a jigsaw.

Place this shaped 2-by-10, which serves as a header, between the king studs and on top of the jack studs. Nail through the king studs into the header with 10d nails to complete the arched window opening.