A door header completes the doorframe and provides support to the structure above the door. Headers for doors can be framed during new construction or during a remodel. The header will be constructed usually by using 2×6, 2×8 or 2×12″ wide boards. Two of them will be attached together with a ½-inch piece of plywood sandwiched in between and installed sideways. The plywood compensates for the difference in thickness from shrinkage ( 2×4′s are actually 1 1/2″ by 3 1/2″) bringing the total width of the header to 3 1/2 inches. The header width must be the same width of the walls which are generally constructed using two by four studs. The size of the header board is dependent on the load bearing that will be needed as well as the size of the opening for the door. A larger opening will need larger wood to bear the load of a large roof.
The header is attached to what is called the top plate. The header vertical length will be greater than the rough opening width. The rough opening is framed by the studs on either side. For a standard load bearing wall there should be two studs per side. The shorter studs called “Jacks” sit under the door header on each side and support the header. Therefore, the header length must be 3 1/2″ longer than the rough opening. When dealing with heavier loads it may be necessary to install 2 Jacks on each side.
Keep in mind 2×4′s shrink and the actual thickness will be 1 1/2 x 3 1/2″ when calculating measurements. The header will be nailed in place below the top plate. Two by four studs will be used to support the top plate by attaching one on either side of the header supports.
The rough opening after framing must be wider and taller than the door to be hung. This is to compensate for the door casing. Framing a door header on walls that are higher than the standard eight feet will require additional framing to compensate for the height. A two by four frame usually called cripple studs will need to be installed below the header. This frame will take up additional space to fit the standard door heights. Standard doors are 80 inches in height but the rough frame in should be between around 83 inches high. The rough opening height must compensate for the door’s threshold.