To install a new window in an existing wall is not all that difficult. You can add a window to a room for added natural light or to get a new view. This article assumes that you have basic carpentry tools and knowledge to use them. You will also need a reciprocating saw(saws-all), circular saw, drill with bits, caulking compound and caulking gun, screw gun with some 2” all-purpose screws and a ladder to be able to reach the window form the outside.
For materials you will need the proper size window, some 2x4’s or 2x6’s depending what you wall was designed with, trim boards to match the outside of you house, some trim for the inside, some pine boards equal at least to the longest dimension of your window, a piece of Z flashing the same dimension as your window’s width and some fiberglass insulation.
Decide where you want the window and mark the wall using a level so that the lines are level and plum. Extend the vertical lines at least 6” above and below the horizontal lines. Using your drill with a wood boring bit of at least 1” cut a hole away from any one of the lines. With the saws-all cut out the square. Try to stay on the lines, but do not be too concerned if you don’t. Once you have the hole completed cut the wall back on both sides to the nearest studs. Then cut an additional 4” higher on the top of the hole and an additional 1 ½” on the bottom. You should now have a hole 5 ½” taller than your window and wide enough to accommodate your new window, but cut back to the nearest studs. There should be a vertical stud or studs in the middle of which need to be cut level with the opening. Once you have cut out the vertical studs you can now start framing in your new window.
Measure the space between the studs of your rough opening. Using the piece of the stud you cut out (if there was one) cut the stud that length. Lay 2x4 or 2x6 on top of the stud you just cut and put a single screw or nail into it (I like to use screws because when using screws you don’t have the pounding of a hammer and they hold better). Now level the board and screw it into the outside studs on both sides of you opening. You have just created the bottom plate that your window will sit on.
Next measure the distance between the two outside studs. Cut two pieces of the dimension lumber you are using to that length. Install both pieces of the lumber on edge next to each other. Make one piece flush with the outside wall and the other flush to the inside wall, there will be a space in the middle.
Next measure the opening required by your window to be sure your original measurements were correct. Measure the distance between the top plate and the bottom plate on each side (they should be the same) and cut two studs and screw them in place. Place the window into the hole to be sure it is going to fit. If it does, great, if not make whatever adjustments needed (another reason to use screws).
Next drill a hole through the outside wall so you can use the saws-all to finish opening the outside wall. If you are planning to put the window trim flush to the sheathing you will have to cut back the outside shingles or siding so the trim boards will fit. Put the Z flashing under the siding. Install the window by sliding the top of the window under the Z flashing. Be sure the window is level and plum. Nail or screw the window into place on the sides only. One or two screws or nails in each corner in sufficient. Caulk the joints between the window and the outside wall to seal out the weather.
Cut and install the outside trim boards and finish as needed. Inside the window will more than likely be short of flush with the finished wall. Using the circular saw (or a table saw) rip the pine boards to the width needed to make the window edges flush with the finished wall. Make the box first then nail it into place with some finish nails equal to twice width of the jumpers that you just made.
Fill all the voids with the insulation. Install sheet rock and finish as needed. When ready trim out the window as desired.
This is not a difficult project to complete but you must have some carpentry skills. I’ve done this type of job many times.