Framing for a Window
Manufacturers of windows specify the size of the rough opening needed. Plan the framing around those dimensions. If the window is wider than 4 feet, temporarily support the ceiling before you cut the opening. The rough sill must be strong enough to support the window. Typically it is made of doubled 2xs laid flat, supported with cripple studs at each end and at 16-inch centers in the middle.
A header over the window is built in the same way as a door header, using 2xs that sandwich a piece of 1/2 inch plywood. The wider the opening, the larger the 2xs should be; consult with your building department or the manufacturer’s literature. When framing for a window, first install the king studs. The space between them should be 3 inches wider than the rough opening required for the window. Cut the jack studs so their tops are even with the top of the rough opening, and attach them to the king studs. Make and install a header to span between the king studs, rest it on the jack studs, and fasten in place.
Cut the lower cripple studs 3 inches shorter than the rough opening and attach one to each jack stud. For the rough sill, cut two pieces to span between the jack studs. Set one of the pieces in place, and fasten it to the cripples. Install cripples in the middle and fasten them. Set the second rough sill piece on top of the first and fasten it. Cut additional cripple studs to fit above the header, and fasten them with angle-driven screws or nails.
Framing for Replacement Windows - Custom windows can be ordered from several manufacturers, but are frequently more expensive than standard-size windows. If you are replacing an old window, you may be able to save a significant amount of money if you modify the framing to accommodate a standard-size window. Be aware, however, that some modifications in opening size will require patching and repainting the wall, which can be a time-consuming process.
Installing a Window
Installing windows up to 3 1/2 feet wide can be a do-it-yourself project, but it does require some advanced framing experience. You must know how walls go together and how to keep everything plumb, level, and square. Carefully plan the window location. Will you run into plumbing, heating, or electrical lines? It’s relatively easy to relocate wiring, but difficult to move pipes or ductwork. Make sure you know the rough-in dimensions of the new window. The exterior opening has to be only slightly larger.
Tools: Hammer, chisel, pry bar, carpenter’s square, keyhole saw or reciprocating saw, nail set, utility knife, caulking gun, drill, carpenter’s level, circular saw, and drywall or plaster tools.
Ease Demolition with a Reciprocating Saw - A reciprocating saw is mighty handy when it comes to tearing into walls. Have several blades on hand, because chances are you will cut through some nails and need to replace the blade. However use a reciprocating saw only when you are sure you will not hit any electrical cables, pipes, or ductwork. When cutting blindly through drywall, turn off the power and use a keyhole saw; that way, you can feel any obstructions.
1. Cut the wall. Mark the opening and cut from ceiling to floor along the adjacent studs; leave the sole plate intact. Make an access hole with a chisel, then a keyhole saw. Or better yet use a reciprocating saw, as shown.
2. Cut the studs. Remove studs interrupted by the window. Using a circular saw and a handsaw or reciprocating saw, cut through a stud in its center, and pry both pieces away from the sheathing. You may need to install a king stud on each side. Slip it between the drywall and the sheathing and fasten it.
3. Add jack studs. Using 16d cement-coated sinkers or 3-inch general-purpose screws, attach 2x4 or 2x6 jack studs to the studs at each side of the opening. They should be as tall as the desired rough opening. The jack studs support the window header.
4. Build a header. Build a header, using two 2 x6s with a scrap of 1/2-inch plywood sandwiched between them. For a very large window, 2x8s may be required. Set the header on top of the jack studs. Drill pilot holes and drive nails or screws at angles to attach the header to the studs.
5. Construct a sill. Construct a 2x4 sill, supported by cripple studs. Set the two outside cripple studs first. Nail 2x4s between the header and the sill to frame side jambs at the rough-in dimension width.
6. Cut the exterior sheathing. Cut out the exterior sheathing and siding from either the inside or the outside. If you cut from outside, first drill pilot holes to mark corners. Check that the rough opening is the correct size, and that it is level and plumb.
7. Trace and cut the siding. Windows are heavy, so have a helper assist you. Set the window in place from the outside, level and plumb, then trace around its molding. Use a circular saw, then a chisel to cut away the siding (not the sheathing) to the trace line.
8. Nail the window to the framing. Cover the exposed sheathing and the inside of the framing with roofing felt (tar paper). Set the window in place and drive galvanized fasteners through the molding. The fasteners should penetrate at least 2 inches into the framing.
9. Nail the jambs to the studs. Inside, insert shims and check that the window operates smoothly; don’t wedge the shims too tightly. Fasten the window jambs to studs. Insulate between the frame and studs, patch and paint the interior wall, attach the inside casing, and caulk the exterior.
Other Installations - To install a metal window, you may not need to cut the siding (Step 7). Nail the window flange directly to the siding. Then install pieces of exterior trim around the window. If you have a brick wall, cut the bricks using a circular saw equipped with a masonry cutting blade. Purchase a window with masonry clips, which bend over and are attached using masonry screws. Install molding after the window is in place.