When I started framing houses in the late 1970s, the standard header for almost any size window and door opening was a double 2×12 with a 1⁄2-in. plywood spacer to bring the header flush with the stud edges in a 2×4 wall. When the header is pushed hard to the double top plate of an 8-ft.-high wall, its bottom sets up window and door head jambs 6 ft. 10 in. off the floor, perfect for standard 6-ft. 8-in. doors. When high-performance homes gained market share in the late 1980s, the building industry looked for options to reduce the amount of lumber used to build headers—or to eliminate conventional headers altogether—in order to save resources, minimize thermal bridging, and provide more space for insulation. Double 2×12 headers are often oversize for the load, but they’re still the standard. In most cases, there is no structural advantage to installing headers that are larger than required, and there are downsides. Not only do they cost more than right-size headers, but the deeper a lumber header is, the more likely it is to lead to drywall cracks as green lumber dries or dried lumber expands during seasonal humidity changes.
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