This story shows you how to install a bay window.
The farther a bay window protrudes from the house, the more dramatic the effect and the more it opens a room. You can choose among units that protrude at 45-, 30-, or 10-degree angles; the latter is sometimes called a bow window. Individual windows may be fixed, double-hung, or casement.
A bay unit attaches like a standard flanged window but with some important differences. Some units also require support from above using cables that attach to framing members in the eaves or the wall above. Some require support from below using brackets or a knee wall. Some need both types of support. A smaller bow window may not need this type of support and can be installed much like a standard flanged window.
Plan how you will finish the top and bottom of the bay window. You may be able to purchase a ready-made roof or you may need to custom-build one. The bottom is usually easy to trim out, but you may choose to build a wall down to the ground. In these the roof and skirt are built on the ground and then installed.
A day or two depending on trimwork
Tape measure, drill, hammer, level, stapler, caulk gun, screwdriver, flat pry bar, circular saw
Good carpentry skills
Cut the opening and check for square. You will need one or two strong helpers.
Bay window, exterior casing, 2x4s, shims, caulk, roofing felt or building paper, drip cap, flashing, plywood, roofing, finishing nails, staples, roofing nails, interior trim, casing nails, insulation
Add facia to the skirt. Make the angled cuts with a table saw, power mitersaw, or a circular saw. These angles can be difficult; always try the joint before cutting the piece to final length so you can recut the angle if needed. Tack each piece in place using 6d galvanized box nails. Complete the final nailing only when you are satisfied with all the joints.