IRC 2024 Header Sizing: Beam Size Over Doors and Windows in Load-Bearing Walls

Quick Answer

IRC 2024 Section R602.7 requires a header above every window and door opening in a load-bearing wall. Header size is determined by IRC Table R602.7, which lists minimum lumber sizes based on the clear span of the opening and the building width. Common results from the table: openings up to 4 feet in exterior walls typically require two 2x8s; 6-foot openings require two 2x10s; 8-foot openings require two 2x12s or an engineered alternative in wider buildings.

Under IRC 2024, every header must bear on jack studs with a minimum 1.5 inches of bearing at each end. LVL (laminated veneer lumber) headers are a code-permitted alternative and often provide a shallower depth for the same span. A single-header alternative using doubled 2x lumber on edge is allowed in specific conditions under R602.7.2.

What IRC 2024 Actually Requires

IRC 2024 R602.7 requires that all openings in exterior and interior load-bearing walls be provided with a header spanning the opening. The header must be supported at each end by a minimum of one jack stud (trimmer) and one king stud. For openings wider than 6 feet in exterior walls, the number of jack studs required increases per Table R602.7.1. The header must bear on the jack studs with not less than 1.5 inches of bearing surface at each end.

Table R602.7 sizes headers for building widths of 20, 24, 28, 32, 36, and 40 feet and for ground snow loads of 30, 50, and 70 pounds per square foot (psf). The table is organized by whether the header is supporting one floor plus roof, roof only, or one floor only. Within each load category, the table gives minimum header size as paired 2x lumber (two members standing on edge side by side, with a spacer between them if installed in a 2x6 wall). For example, in a 28-foot wide building with 30 psf ground snow load, supporting one floor plus roof, the table requires: a 4-foot opening — two 2x6s; a 6-foot opening — two 2x10s; an 8-foot opening — two 2x12s; a 10-foot opening requires engineering. Header sizing increases with building width because wider buildings transfer more tributary load to the header.

IRC 2024 R602.7.1 provides a simplified prescriptive method for exterior headers in Seismic Design Categories A, B, and C using single tables without building-width variables when the building is within specific dimension limits (not more than 36 feet wide and not more than two stories). This simplification makes field application easier for standard residential construction and reduces the number of table lookups required.

The 2024 edition updated Table R602.7 to clarify that the building width used in the table is the overall building dimension in the direction of the span — measured from exterior wall face to exterior wall face — not the span of individual framing members. This clarification resolves a longstanding ambiguity where some practitioners used the distance between bearing walls rather than the full building width, which would understate the load and result in undersized headers.

Why This Rule Exists

A header transfers the loads from above an opening — roof, floors, snow — to the jack studs on each side and then down through the king studs, wall framing, and foundation. Without a header, the loads that would have been carried by the interrupted studs must be redirected around the opening through the wall framing, which dimensional lumber alone cannot accomplish efficiently. An undersized header deflects excessively under load, which causes doors to stick or fail to latch, windows to rack out of square, and in severe cases can cause plaster or drywall cracking around the opening. The minimum sizes in Table R602.7 are calibrated to limit deflection to L/360 of the span under live load and L/240 under total load, which are the standard limits for components supporting plaster or drywall finishes.

The requirement for a minimum 1.5-inch bearing at each end ensures that the header load is transferred to the jack stud over a sufficient surface area to avoid crushing the wood fibers at the bearing point. Wood loaded perpendicular to the grain (bearing) is much weaker than wood loaded parallel to the grain; the 1.5-inch minimum creates enough bearing area for the perpendicular-to-grain stress to remain within allowable limits for spruce-pine-fir and similar framing species.

What the Inspector Checks at Rough and Final

At rough framing inspection the inspector checks header size against the approved plans or the prescriptive table, counts jack studs at each opening, measures bearing length at the jack stud to header interface, and verifies that the double top plate is continuous over the header location. A header that is spliced at the centerline of the opening is a common finding that fails inspection; headers must be single continuous members or engineered spliced assemblies, not field-cut pieces butted together over an opening.

The inspector also checks the nailing between the header components. Paired 2x headers must be nailed together with the schedule specified in Table R602.3(1) — typically 16d nails at 16 inches OC through both faces. A header assembled with insufficient nailing can separate under load, reducing the effective section and increasing deflection. When a spacer is used between header members in a 2x6 wall (to bring the header to full 5.5-inch wall thickness), the spacer must be the correct thickness and the nailing must still connect both header members through the spacer.

LVL and PSL headers are inspected for species and grade marks on the member, the correct size per the engineered design or manufacturer’s span table, and proper bearing per the manufacturer’s requirements. LVL members are typically installed with their laminations vertical (on-edge), not flat, and must not be notched or drilled without engineering review of the specific cut location.

What Contractors Need to Know

Select header size from the table before framing begins, not after the rough opening is cut. Know the building width, the ground snow load for the project location (found in IRC Figure R301.2(6) or from the local building department), and the number of floors supported. Cross-reference these against Table R602.7 to find the minimum header size for each opening in the house. An opening in the back wall of a two-story house may require a larger header than an identical opening in a single-story garage, because the supported load category is different.

In 2x6 walls, standard double 2x headers produce a 3-inch-thick assembly in a 5.5-inch wall. The gap must be filled to provide a continuous bearing surface for sheathing nails and to prevent the wall from being weaker at the header location. Fill the gap with a 1/2-inch structural plywood spacer or OSB cut to width and nailed between the header members before installation. Do not fill the gap with insulation foam board alone — foam board does not provide structural continuity between the members.

LVL headers are an excellent choice when the required dimensional lumber header is too deep to fit within the wall framing height available or when the header must support concentrated point loads not addressed by the prescriptive table. A 3.5-inch x 9.5-inch LVL (equivalent to two 2x10s) is typically shallower than the paired dimensional lumber would be for longer spans. LVL is also straighter and less prone to crown and warp, which matters at wide openings where header deflection is a finish quality concern. Size LVL headers using the manufacturer’s published span tables, which are available for specific LVL grades and are typically organized by span, load, and bearing length.

The single-header alternative under R602.7.2 uses a single 2x12 or double 2x10 on edge instead of two members for short spans in non-load-bearing or lightly loaded interior walls. Verify the specific conditions under R602.7.2 before using this alternative — it is not universally applicable and has building width and load restrictions. Using the simplified alternative where the prescriptive table would require a larger member is a common violation that can be easily caught at inspection.

What Homeowners Get Wrong

Many homeowners and DIY remodelers assume that a 2x6 laid flat above an opening is sufficient as a header for a small window or door. A flat 2x member has far less bending stiffness than the same member standing on edge because stiffness scales with the cube of the depth. A 2x6 on edge is roughly nine times stiffer in bending than a 2x6 laid flat. The code requires headers to be installed on edge for this reason. A flat header — even a doubled 2x6 flat — will deflect many times more than a code-compliant on-edge header under the same load, causing doors and windows to bind and trim to crack.

Another common misunderstanding is that removing a wall and installing a beam only requires sizing the beam for the floor above. The header or beam must also account for roof and snow loads if the wall being removed is in the load path from the roof to the foundation. Homeowners who remove interior walls without evaluating the load path sometimes install a beam sized only for floor loads, which is undersized for the actual combined load the beam must carry. This error does not show up immediately but causes progressive deflection and cracking over years.

State and Local Amendments

California’s CBC (California Building Code) follows the same header sizing approach as IRC Chapter 6 for one- and two-family dwellings regulated under the California Residential Code. However, California’s high seismic requirements in SDC D and E mean that many wall configurations require engineered design rather than prescriptive tables, which effectively takes header sizing out of the IRC table and into engineering calculations. Florida Building Code allows the IRC prescriptive headers in wind zones up to 130 mph but requires engineering review for coastal high hazard areas. Some counties in Florida with adopted amendments require stronger connections at header-to-jack stud interfaces than the basic IRC nailing schedule. Check with the local building department for any adopted amendments to Table R602.7 before finalizing a design.

When to Hire a Professional

A structural engineer is required when the opening span exceeds the limits of IRC Table R602.7 (typically over 10 feet in exterior walls), when the header supports a concentrated point load from a post or beam above, when removing an interior wall that is part of the load path, when the building width, snow load, or number of floors supported places the design outside the table’s range, or when the building is in a high-seismic or high-wind zone that requires engineered bracing affecting the header design. Engineers typically provide a stamped design that specifies header species, grade, size, bearing length, and connection hardware, which the contractor follows during installation and the inspector reviews at rough framing.

Common Violations Found at Inspection

• Header is undersized for the span and building width per Table R602.7, typically because the contractor used the table for a narrower building width or lower snow load than the project actually requires.
• Header members are not nailed together at the required schedule, leaving the paired members able to separate under load and reducing the combined section capacity.
• Jack stud count is insufficient for the opening width; wider openings require two jack studs per side but only one was installed, concentrating the header reaction on a smaller bearing area.
• Header bearing length at the jack stud is less than 1.5 inches because the jack stud was cut short during rough-in or the rough opening was widened in the field without adjusting the framing.
• LVL header is installed with laminations horizontal (flat) instead of vertical (on-edge), which reduces the effective depth and greatly increases deflection under load.
• No spacer between header members in a 2x6 wall, leaving a 2-inch gap through the header that interrupts the sheathing nailing surface and allows the header members to act independently rather than as a composite section.
• Header is spliced at midspan with two pieces butted together, a non-code-compliant connection that has no bending resistance at the splice point.
• Single 2x member used as a header in a load-bearing wall without meeting the specific conditions of the R602.7.2 alternative, which requires verifying load limits and building dimensions before applying the simplified method.