This story shows you how to install a flanged window.
Metal and vinyl windows have an integral flange (also known as a nailing fin) that attaches to the house. Once the flange is firmly fastened, there is no need to anchor the window jamb.
Carefully seal the house's sheathing correctly so water flows away from the house and cannot be trapped next to the sheathing. The sealing instructions on these pages will suit most situations, but your window may come with different instructions or your local building department may have different requirements.
Choose a metal or vinyl window that feels solid when you try to twist it and has substantial weatherstripping. Buy from a well-established manufacturer so you can easily buy replacement weatherstripping and other parts if needed in the future.
Several hours (working with a helper if the window is large) to install the window and trim
Tape measure, drill, hammer, level, stapler, caulk gun
Basic carpentry skills
Cut the opening and check for square. Buy a flanged window to fit.
Window, exterior casing, shims, caulk, roofing felt or building paper, drip cap flashing, other flashing (such as self-stick) if required by codes, finishing nails, staples, galvanized roofing nails
Set the window in the opening, pressed against the siding, and drive a screw at the center of the top flange. Shim as needed so the window is square and the sashes work smoothly and are aligned with the frame. Drive three or four more screws through the flanges to hold the window in place temporarily.
Cut 10- to 12-inch-wide strips of roofing felt or building paper. Slip them behind the siding, wrap them around the framing, and staple in place. First install the piece at the sill, then the sides, then the top piece. Finally cut four pieces about 4 inches square and slip them into the corners to cover the V-shape gaps.