Header Sizing for Windows and Doors: What You Need to Know
What a Header Does
A header is a horizontal beam that spans a window or door opening, transferring the load above the opening to the jack studs (trimmers) on each side. Without a properly sized header, the weight of the wall, floor, and roof above the opening has no load path to the foundation.
In bearing walls, headers carry real structural load. In non-bearing (partition) walls, a flat 2×4 header is technically sufficient — but most builders install full headers in all walls for consistency and future flexibility.
Standard IRC Header Sizes
The IRC provides prescriptive header sizes for conventional wood-frame construction. These apply to one-story situations or the top story of multi-story buildings with standard roof loads.
For a bearing wall supporting one floor, ceiling, and roof with a standard 40 psf live load and 10 psf dead load:
Up to 4-foot opening: double 2×6 header. Up to 6-foot opening: double 2×8 header. Up to 8-foot opening: double 2×10 header. Up to 10-foot opening: double 2×12 header.
These are for Douglas Fir-Larch or Southern Pine No. 2 grade. Weaker species may require upsizing.
“Double” means two members nailed or bolted together with a 1/2-inch plywood spacer between them to match the 3-1/2 inch wall depth (for 2×4 walls) or built to 5-1/2 inches (for 2×6 walls).
When Standard Tables Don’t Apply
The IRC prescriptive tables cover specific conditions. You’re outside the tables when: the wall supports more than one floor above (multi-story interior bearing walls), the opening exceeds 10 feet, the roof load exceeds the standard assumption (heavy tile roof, snow load region), or the header is in an exterior wall with unusual geometry.
In these cases, an engineered header is required — either designed by calculation or using an engineered lumber product (LVL, PSL, or glulam) with the manufacturer’s span tables.
LVL Headers
Laminated Veneer Lumber (LVL) headers span farther than solid-sawn lumber at equivalent depth. A single 1-3/4 × 9-1/4 inch LVL can often replace a double 2×10 solid header, and LVLs are available in depths up to 18 inches for large openings.
LVL headers are standard for garage door openings (16+ feet), large window assemblies, and any opening where solid-sawn lumber can’t carry the load at an acceptable depth. They cost more per foot than framing lumber but enable openings that would otherwise require steel.
Jack Studs and Point Loads
The header transfers its load to the jack studs. Each jack stud must be capable of carrying half the header’s total load (for a symmetrical opening). For most residential openings, a single jack stud per side is sufficient. For large openings or heavy loads, double jack studs may be required.
The point load at the base of each jack stud must also be accounted for — it transfers down through the floor framing to the foundation. In multi-story construction, headers at the top floor create point loads that stack all the way down. This is where an engineer earns their fee: tracing the load path from the roof through each floor’s header to the foundation.
Common Mistakes
Using a header table for the wrong load condition. An interior bearing wall supporting a second floor AND a roof carries more load than a wall supporting only a roof. The header sizes differ — using the lighter table for the heavier condition undersizes the header.
Forgetting the header in non-bearing walls. While structurally unnecessary, headers in non-bearing walls provide future flexibility. If the homeowner later adds a second story or modifies the load path, having headers already in place avoids expensive retrofits.
Not checking the jack stud bearing. A correctly sized header on inadequate jack studs fails just as surely as an undersized header on adequate supports.