Whether you're building a new home, removing an older window frame, or adding a new one in an existing wall, there are a few core elements to framing a window. It's a big project, but it only takes a few tools and materials, so you can definitely pull it off. You'll probably start with some demolition if you don't already have an opening. Here's what to do next.
1. Measure the Rough Opening
Measure the vertical and horizontal sides of the opening for the rough frame, and take care to set its dimensions 1-1/2 inches wider and taller than the window you want to install.
Measure another three inches on each side for the king studs and the jack or trimmer studs. If there's a wall stud right up close that can be used as one of the framing king studs, building from that will save you extra work and lumber.
The king studs are the main vertical posts that run from the bottom wall plate to the wall frame's top wall plate on each side of the window. The jack studs are shortened vertical posts fitted between the header and bottom wall plate (or soleplate).
They're nailed to the king studs on both sides of the window to support the header, which is the large horizontal piece at the top of the opening that runs the full width of the window opening and sits on top of the jack studs.
Cripple studs are short vertical posts placed between the header and the top wall plate and underneath the sill and the soleplate's opening.
2. Cut, Fit, and Nail the King Studs
Cut the king studs so they connect the top wall plate with the soleplate and fit on the outer edge of the opening. Nail them to the top plate and the soleplate. The wall framing's top plate is usually a double plate and is the horizontal beam where the ceiling joists are resting.
The soleplate is the horizontal beam at the bottom, where the wall meets the floor. Use two nails for each end, and check that the beams are plumb with a level.
3. Place the Jack Studs
Cut the jack studs, making sure their height is 3/4 inch longer than the height of your window's header once installed. Place them inside the window opening against the king studs and nail them together on both sides of the window opening.
4. Cut and Fit the Header
The header is the large horizontal beam at the top of the window framing. Measure, cut, and nail together two sections of 2x6 or 2x8 lumber, and position them on the top of the jack studs. Toenail the header into the king studs so that they come flush to the wall frame on both sides.
Since the two adjacent pieces only add up to three inches, an in-between spacer can be made from 1/2 inch plywood to make up for the 3-1/2 inches thickness of the wall frame.
5. Install the Window Sill
Cut the sill to the length equal to the distance between the jack studs. Mark at every 16-inches on the soleplate and the sill piece, where you'll need to place cripple studs. Cut as many pieces as needed from 2x4 lumber.
Nail all the cripple studs to the sill plate, then take that sub-assembly and place it between the jack studs within the wall frame. You can then toenail the sill to the jack studs and the cripple studs to the soleplate. For good measure, you can add up two extra cripple studs against the jack studs for more stability.
6. Place the Top Cripple Studs
Mark on the top wall plate and on the header where you will need cripple studs, every 16-inches apart. Measure the height between the top wall plate and the top of the header and cut as many cripple studs as required from 2x4 lumber.
You can also add two extra pieces here for stability. You can then toenail the shorter studs in place between the header and the top plate. This is the last step in how to frame a window.