A window header are a horizontal beam that is placed above a window opening. The beam carry the weight of the structures located above the window opening. The window header balance the weight of the roof, the upper floor joists, and the weight of the wall itself.
If the header is of a correct size for the window opening, the window frame will remain square for the life of the structure. However, if the header is of incorrect size for the structure, the frame will sag, the sashes will stick within the window frame, and the structure will require expensive repair. The width of the window and the height of the building influence the size of a window header.
Window Header: What It Does and How to Install It
A narrow window opening in a single-story house may require a header made of double two-by-sixes. A wide window opening in a two-story house may require an engineered lumber header. This is because a header in a two-story house must balance the weight of the roof and the second floor floor joists.
The header in a single-story house only need to balance the roofs weight. Because of the extra weight that the header in a two-story house must balance, the header must be of a larger size or made of stronger material, such as LVL or PSL beams. The framing anatomy for installing a window header include other components beyond the header itself.
King studs are full-height studs located beside the opening. Between the two king studs is the jack studs. The jack studs receive the weight of the window header, so you must place the header directly on the jack studs.
Also included in the framing anatomy are the cripple studs, which are studs placed between the window header and the window sill. The header cannot function correctly without the jack studs being present and of sufficient size. The header also require these other components in its framing anatomy to properly distribute the structural loads.
The solid lumber or engineered lumber for the header must be choose carefully based off the width of the opening and the weight of the load that must be balanced. If the header is to be made of doubled dimensional lumber, it is appropriate for span opening of up to eight feet. This is because doubled dimensional lumber is the most cost-effectively lumber for this job.
However, if the opening is wider than eight feet, the beams will deflect under the weight of the structure. In this case, you should use LVL beams. Because engineers design LVL beams to be free of knots in the lumber and plane them to avoid warping, the beams are more stable.
Where you decide to install the window in the wall also has an effect on the size of the window header. If you install it into a load-bearing wall that support the weight of the floor joists or the ridge board, the header will have to meet the requirements of the span tables for load-bearing walls. If you install the window into a non-load-bearing wall that does not support floor joist, the header can be smaller in size.
When installing a window header, there is a specific sequence to the installation. First, you will mark the king studs and the jack studs on the plates. Next, install the king studs to their full height.
Install the jack studs between the two king studs. Place the window header on top of the jack studs. Finally, install the cripple studs between the header and the window sill.
If you skip any of these step, the windows frame will sag once the drywall is hung on the studs. As with all project, people tend to make mistakes when installing a window header. One mistake is using a header that is too small for the job to save money on the lumber for the header.
A second mistake is forgetting the code requirement for a header that is larger than what the span table say. Both of these mistakes will result in the window frame sagging. To avoid these mistake, ensure that the header is balanced with the load table for the building.
With an understanding of each of these factor, it is possible to choose the appropriate size for the window header.
