Header

A header is a horizontal structural beam installed above a door or window opening in a wall, designed to carry the load that would otherwise pass through the section of wall removed to create the opening. Whenever a wall is interrupted by a doorway, window, or other opening, the header spans that gap and transfers the weight from above down into the framing members, called king studs and trimmer studs, on either side of the opening. Every opening cut into a wall needs some form of header, though the required strength differs significantly depending on whether the wall is load-bearing.

Header sizing is one of the more consequential calculations in residential framing because it directly affects whether a Load-Bearing wall continues to safely support the structure above an opening. The Door Header Size Calculator uses the opening's width along with the load coming from the roof, floors, or joists above to recommend a header depth and material, following standard span tables used throughout residential construction.

Headers work in tandem with the rest of a building's structural system, particularly the Joist members that rest on the walls the header is helping to support. A header that is too shallow for its span and load can deflect or crack, leading to visible problems like sticking doors or cracked drywall directly above the opening, which is why proper sizing before construction is far cheaper than repairs after the fact.

• Header size depends on load-bearing status. A header in a Load-Bearing wall must be structurally sized to carry real weight, while one in a partition wall is mostly for framing convenience.
• Wider openings need deeper headers. As an opening's width increases, the header must get deeper or be made from a stronger material to span the gap without excessive sag.
• Load from above compounds the requirement. A header supporting multiple floors or a long run of Joist members overhead needs to be sized for that cumulative load, not just the roof alone.
• King and trimmer studs share the load. A header only works properly when paired with adequately sized studs on either side of the opening to carry its load down to the foundation.
• Engineered lumber allows wider openings. Laminated veneer lumber and steel headers can span wider openings than solid dimensional lumber at the same depth, which is useful for large window walls or garage door openings.