Open up a wall and the studs you remove were carrying weight, from the floor above, the roof, or both. A header is the beam that picks up that load and carries it to the studs on either side of the new opening. Size it too small and the opening sags, doors bind, drywall cracks, and in the worst case the structure above settles. Sizing a header correctly is not guesswork; it follows from the load, the span, and the lumber you use.
What the header actually carries
A header in a load-bearing wall supports everything above the opening that used to bear on the removed studs: floor joists, the wall above, roof loads transmitted down. The wider the opening and the more structure above, the greater the load. A header over a closet door in a single-story home carries far less than a header spanning a wide opening below two floors and a roof.
The first job is determining whether the wall is load-bearing at all. Walls running perpendicular to floor joists, walls stacked over beams or walls below, and exterior walls generally carry load; walls running parallel to joists often do not. When in doubt, assume it bears load until a qualified evaluation says otherwise. This is structural work, and the cost of being wrong dwarfs the cost of checking.
How sizing works in principle
Header sizing balances three variables: the load per foot along the header, the clear span of the opening, and the strength and stiffness of the header material. Longer spans and heavier loads demand deeper, stronger headers. A doubled 2x4 header that suffices for a narrow doorway fails over a wide opening because deflection grows with the cube of the span; doubling the span needs roughly eight times the stiffness for the same sag.
Building codes contain prescriptive header tables that size common cases without engineering calculations: given the opening width, the number of floors supported, and the building width, the table names the header. These tables are conservative and straightforward to use. Anything outside the tables, unusually wide openings, heavy loads like tile roofs or masonry above, or engineered lumber, calls for actual engineering rather than extrapolation.
Choosing the header material
Traditional headers are built up from doubled or tripled dimensional lumber, two or three 2x members nailed together with the crowns aligned, sized to match the wall thickness. For a 2x4 wall, doubled 2x material with plywood spacers fills the wall depth. Engineered lumber, laminated veneer lumber or parallel strand lumber, offers greater strength and stiffness per inch of depth, allowing shallower headers where headroom matters, at higher material cost.
Whatever the material, the header must bear fully on its supports. Jack studs under each end carry the header's load down to the bottom plate; king studs alongside tie the assembly into the wall framing. Skimping on the jack studs, a single jack where two are needed, or letting the header bear on a partial support, undermines the whole sizing exercise.
Installation details that matter
Support the structure above before cutting. Temporary walls or shoring on both sides of the opening carry the load while the header goes in; removing studs from a loaded wall without shoring invites sudden settlement. Build the header assembly, set it level on the jack studs, and fasten per the nailing schedule; a header that is not level or not fully bearing loads unevenly.
Check the load path all the way down. The header's load travels through jack studs to the bottom plate, then to whatever is below: a foundation wall, a beam, or another framed wall. If the opening sits over a basement or crawlspace, verify that the point loads land on adequate support below, not on mid-span floor joists that were never meant to carry them. Blocking or a post below may be needed to complete the path.
When to call an engineer
Prescriptive tables cover standard residential cases. Call a structural engineer for openings wider than the tables cover, walls supporting masonry or heavy roofing, any sign of existing structural distress like sagging or cracked framing, and multi-story load paths that are not obvious. An engineer's stamp also smooths permits and inspections, which most jurisdictions require for structural wall modifications.
Pull the permit. Structural framing changes without permits create problems at resale, with insurance, and with inspectors who notice. The permit process also gives you a second set of eyes on the sizing, which is cheap insurance on structural work.
Header sizing is load, span, and material, resolved through code tables or engineering, installed with proper shoring and a complete load path. Respect the sequence and the structure above the opening stays exactly where it belongs.
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