Definition
A header is a horizontal structural member placed above doors, windows, and other openings in a wall to support the load from above. Headers transfer weight from the structure above to the vertical trimmer or king studs on either side of the opening. Headers are typically made from dimensional lumber (2x, 4x), engineered wood, or steel depending on the load and span requirements.
Formula
The header must extend at least 3 inches beyond each side of the opening (6 inches total) for proper bearing. Header depth depends on span length-for openings up to 6 feet, use 2x6 or 2x8; up to 8 feet, use 2x10 or 2x12; larger spans require engineered lumber or steel. Always consult local building codes and span tables.
Example
Header Sizing Example
For a standard 6-foot exterior door opening in a load-bearing wall: Use a 4x6 or double 2x6 header with 1/2 inch plywood spacer. The header length is 75 inches (6 feet 3 inches) to allow 3-inch bearing on each side. The header rests on jack (trimmer) studs, which transfer the load to the king studs and foundation below.