How To Build Window and Door Headers in Walls (page 2 of 3)

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How To Build Window and Door Headers in Walls-Page 2

Headers take the weight of the materials and occupants above and transfer it via the trimmers down to the floors and foundations below. Longer openings require larger headers. Bearing walls (those that carry the weight of joists and trusses) require larger headers than non-bearing walls.

Together the headers, king studs and trimmers act as a system that transfers weight from above, down and around the window and door openings to the floor and foundation below. The longer the distance a header spans and the heavier the load it supports, the more substantial it needs to be. Undersized headers will bow downward, pinching windows and doors and making them difficult to operate. They will also crack drywall and distort trim. There is no simple rule of thumb to determine exactly what size a header should be. But you gotta get it right.

Hey Einstein, How Big Should That Header Be?
Calculating header size is complicated. You have to take into account: (1) the length of the window or door opening; (2) the combined weight of the floors, walls and roofs above; (3) the building width; (4) the snow load in the area; (5) whether it’s a bearing wall (where joists, trusses and rafters rest) or a non-bearing wall (to which joists, trusses and rafters run parallel); (6) whether it’s an exterior or interior bearing wall; and (7) what species of wood you’re working with.

The 2000 International Building Code book contains two full pages of mind-numbing charts for calculating proper header sizes in different situations. As you’d expect, the deeper the header, the longer the distance it can span. But trust me, you don’t want to wade into all the technicalities. There’s no simple formula. My advice is this:

Have an engineer or architect calculate the required header size for your window and door openings.
Ask your local building code official to help you calculate header size. It’s usually not in their job description, but the nice ones will help you out.
When in doubt, build a double 2x12 header sandwich like we explain next. In all but the most bizarre situations, they’ll easily carry the weight for 4-ft. wide window and door openings and, in most situations, be code compliant for openings up to 6 ft. wide—a common patio door width.

FIG. A