Dormer windows are available in various styles: gabled, shed, hipped, segmental or eyebrow. In the case of eyebrow dormers, also known as arched dormers, there may be various options when installing windows. While it would be easier to install a rectangular window, for aesthetic reasons you may prefer an arched window. This may be more expensive, and will require extra care when installed.
Step 1 - Mark the Wall
Using the pre-cut arched window, mark the wall, so you can use these guiding points when cutting the opening of the dormer window. When marking the wall, make sure to add two inches to the actual size of the arched window, for the frame.
When you measure the curve for the window, first measure the distance between the two vertical sides of the arched window. Measure the bottom width of the window, and mark the points where this width starts to decrease (the corners of the arch). Measure the distance between the two arch corners, and you obtain the diameter of the arch.
Divide the diameter by two, to obtain the radius of the arch. This will be the distance from the center of the diameter to any point on the arch. Cut a string the size of the radius, plus an additional two inches, for the frame. Use a pencil and this string to mark the arch on the wall.
Step 2 - Make the Opening in the Drywall
Use a circular saw, and follow your marks to cut an opening in the drywall. To cut the curve in the wall, drill several small holes on the arch that you’ve marked on the wall. Use a hammer to remove the wall.
You may need to remove the insulation from the interior of the wall, and if there are studs, you need to cut them, so that you can install the windows. Cut the studs with a reciprocating saw.
Step 3 - Cut the Opening in the Exterior Wall
Cut the opening in the exterior wall, using the reciprocating saw.
Step 4 - Build the Window Frame
The easiest way to build the frame is to get a wooden arch and two pieces of 2x4 lumber. Cut two equal pieces of lumber, and one piece for the length of the frame. Glue the arch and the pieces of lumber together, and then nail them with framing nails. You can paint the frame at this time, but this means that you will have to wait for the paint to dry before you can go on to the next step. You may also paint the interior of the frame after you have secured the window.
Step 5 - Insert Window Into Frame
Buy ready cut arched window to the size you need (1/10 of an inch smaller than the frame). Insert the window into the frame.
Put the nailing fins of the pre-cut arched window against the frame. Nail the frame to the top of the arch and the bottom of the window. Add shims if you need to adjust the level, and then insert nails in every second hole of the window’s fins.
Use polyurethane foam to finish and insulate the room, and patch the drywall as necessary.