While many factors contribute to a window's lifespan and its ability to stand up to the elements, its framing is one of the most important factors. When well-built, a window frame is just as important to the overall function of the window as the window itself.
What is a Window Frame?
A window frame is the collection of studs within a wall system that holds the window in place. Support comes from below (window sill and support studs), on the sides (king studs and jack or trimmer studs), and from above (the header and more vertical supports).
Accurately built window frames are important. Overly tight framing can push the window out of square. Framing that contracts over time can crack the window and even break the glass. When the window is framed too loosely, this can let moisture into the wall system.
If you get the window frame right, window installation will be much easier.
Elements of a Window Frame
- Top and Bottom (Sole) Plates: A top plate is the long horizontal two-by-four that runs the length of the house, at the very top. Similarly, a bottom plate runs the length of the house on the flooring.
- Window Header: The window header is a pair of horizontal two-by-fours (or wider boards for larger windows) that run the width of the window frame. They are positioned on-edge, with a third two-by-four attached to form the inside of the window frame.
- Short Support Studs (Top): Short vertical studs run between the window header and the top plate.
- King (or Regular) Stud: The building element that forms the outermost sides of the window—the king stud—runs between the top plate and the bottom/sole plate. There are two king studs, one on each side.
- Jack (or Trimmer) Stud: The jack or trimmer stud begins at the bottom/sole plate and runs vertically upward until it reaches the bottom of the window header. It rests against the king stud, on the inside. There are two jack studs, one on each side.
- Sill Plate: The sill plate is a horizontal stud that runs between the two jack studs. It rests on the short bottom support studs.
- Short Support Studs (Bottom): Short vertical studs run between the sill plate and the bottom (sole) plate.
Equipment / Tools
- Framing hammer or nail gun
- Speed Square
- Tape measure
- 6 Two-by-fours
- 2 Two-by-sixes
- 16d nails
Measure the Window
With the tape measure, measure the height and width of the window to be installed. Measure the window's frame, the part that will slide into the window rough opening that you will be building. Do not measure the nailing fins that will attach to the side of the house. Take those measurements and add 1/2-inch on all of the four sides to arrive at your rough opening dimensions.
Build the Window Header
Cut two two-by-sixes to the width of the rough-in, plus another 3 inches. Nail the two pieces together with two nails every 16 inches. Do this on both sides. Cut one two-by-four to the same length and attach it to the bottom of the two-by-six assembly.
Larger framing members than two-by-six may be required, depending on the width of the window and the load supported from above. Check with building department or engineer for proper sizing.
Add the King Studs
Use the window header as a type of measuring stick to establish the positions of the two king studs on the top and bottom plates. Nail the king studs into place.
Add the Jack Studs
Dry-fit the header between the two king studs. Lay it in the intended vertical position. Measure downward from there to arrive at the length of the jack studs. Cut two two-by-fours to that length. Nail the jack studs into the king studs, ensuring that the jack studs touch the top of the sole or bottom plate.
Cut and Install the Bottom Vertical Supports
Cut four of the two-by-fours as the bottom vertical supports. These boards should be three inches shorter than the height of the window sill plate. This is because you will be installing a doubled-up two-by-four sill plate, and each two-by-four is 1-1/2 inches thick. Nail two against the jack studs, then nail two more in the center section.
Cut and Install the Window Sill Plate
Measure the distance between the two jack studs. Use that dimension to cut two two-by-fours. Nail them together as a double window sill plate. Nail on top of the four bottom vertical supports.
Install the Window Header
Nail the window header on top of the two jack studs.
Cut and Install the Top Support Studs
Measure the distance between the top of the window header and the bottom of the top sill plate. Cut three pieces of two-by-four to that length. Toenail these pieces vertically in that section.