Window and Door Header Size Requirements — IRC 2018

Quick Answer

IRC 2018 R602.7 and its tables govern header sizing over windows and doors in bearing walls. Header size depends on the opening width, number of stories above, and building width. A common 4-foot window opening in a single-story house with a bearing wall typically requires a 4×6 or built-up 2×6 header. Larger openings and multi-story applications require larger headers per Table R602.7.

What R602.7 Actually Requires

Section R602.7 requires that headers be provided over openings in load-bearing walls. The prescriptive header sizes are given in Tables R602.7(1), R602.7(2), and R602.7(3) for supporting conditions with different numbers of stories and roof configurations. The tables specify minimum header size based on the clear span of the opening (the distance between king studs) and the building width (which determines the tributary load on the header).

The tables are organized by: (1) exterior bearing walls supporting a roof load only, (2) exterior bearing walls supporting one floor plus roof, and (3) interior bearing walls supporting various configurations. The header size options given in the tables include built-up lumber (2 − 2×4, 2 − 2×6, 2 − 2×8, 2 − 2×10, 2 − 2×12), solid sawn lumber (4×, 6×), and LVL equivalents.

For a 6-foot opening in a single-story building (roof load only) with a 28-foot building width, Table R602.7(1) shows a minimum of 2 − 2×10 or 4×10 for the header. For the same opening supporting one floor plus roof (two-story application), the header size increases to 2 − 2×12 or 4×12 in many cases. Header sizes increase with wider openings and greater tributary loads.

Built-up headers must be assembled from the same species and grade. A 2 − 2×10 header made from mixed species has an effective size governed by the weaker species — mixing species in a built-up header is not permitted without engineering review.

Headers are framed with king studs on each side of the opening (full-height from bottom to top plate) and jack studs (trimmer studs) under each end of the header to provide bearing. The jack stud count required varies by opening width per the table.

Why This Rule Exists

When a wall stud is removed to create an opening for a window or door, the load that would have been carried by those studs must be redirected around the opening. The header spans the opening and carries this transferred load to the king studs and jack studs on each side. An undersized header deflects under load, cracking drywall at the corners of the opening, causing the window or door frame to rack and stick, and potentially creating structural distress if the deflection is severe enough to shift the roof system above.

What the Inspector Checks at Rough and Final

At the framing inspection, headers are checked for:

• Header size consistent with the applicable table for the opening width, building width, and story count.
• Header species and grade stamps on built-up members.
• Number of jack studs (trimmers) under each header end per the nailing and framing table requirements.
• King stud presence and full height from plate to plate.
• Header fastening to king studs — typically 3 − 16d nails per end per Table R602.3(1).
• For larger openings with multiple jack studs, correct doubling of jack studs per the table.
• Header bearing — the header must bear fully on the jack stud, not bridging a gap.

What Contractors Need to Know

Install the header flush with the top of the wall framing to allow installation of the top plate and to ensure the header bears fully on the jack studs. A header set below the top plate creates a cripple space above it that requires additional cripple studs and complicates the framing.

Use a 1/2-inch spacer (plywood scrap) between double-2× built-up headers to match the 3.5-inch wall width for 2×4 walls — two 1.5-inch members = 3 inches, which does not fill the wall cavity. The spacer brings the total header width to 3.5 inches, allowing proper attachment of sheathing and interior finish. For 2×6 walls, the spacer thickness is greater (1.5 × 2 = 3 inches versus the 5.5-inch wall depth) — specify accordingly.

LVL headers are increasingly used for larger openings and provide consistent size, no crown, and reliable structural properties. When substituting LVL for the built-up lumber table value, verify the LVL manufacturer's span table for the equivalent design.

The tables apply to standard load conditions with conventional spans and loading. When a window or door opening is located under a point load from a flush beam above, the header must be engineered for the point load, not just selected from the table. Similarly, when an opening is in a gable end wall that also serves as a braced wall line, the header must carry both gravity load and in-plane shear from the bracing requirement. This combined loading case may require engineering verification before relying on the prescriptive table selection.

Header-to-king-stud and header-to-jack-stud connections must be made with the required nailing schedule from Table R602.3(1). The top of the header is nailed to each king stud, and the jack studs are nailed to the trimmer studs at the specified spacing. Builders sometimes frame the header and kings as an assembly on the deck before standing the wall but forget to add the required nail count at each connection point. Review the nailing schedule during rough framing inspection because missing nails at header connections are a commonly cited deficiency that is straightforward to prevent with a pre-inspection review of the nailing pattern.

The tables apply to standard load conditions with conventional spans and loading. When a window or door opening is located under a point load from a flush beam above, the header must be engineered for the point load, not just selected from the table. Similarly, when an opening is in a gable end wall that also serves as a braced wall line, the header must carry both gravity load and in-plane shear from the bracing requirement. This combined loading case may require engineering verification before relying on the prescriptive table selection.

Header-to-king-stud and header-to-jack-stud connections must be made with the required nailing schedule from Table R602.3(1). The top of the header is nailed to each king stud, and the jack studs are nailed to the trimmer studs at the specified spacing. Builders sometimes frame the header and kings as an assembly on the deck before standing the wall but forget to add the required nail count at each connection point. Review the nailing schedule during rough framing inspection because missing nails at header connections are a commonly cited deficiency that is straightforward to prevent with a pre-inspection review of the nailing pattern.

The tables apply to standard load conditions with conventional spans and loading. When a window or door opening is located under a point load from a flush beam above, the header must be engineered for the point load, not just selected from the table. Similarly, when an opening is in a gable end wall that also serves as a braced wall line, the header must carry both gravity load and in-plane shear from the bracing requirement. This combined loading case may require engineering verification before relying on the prescriptive table selection.

Header-to-king-stud and header-to-jack-stud connections must be made with the required nailing schedule from Table R602.3(1). The top of the header is nailed to each king stud, and the jack studs are nailed to the trimmer studs at the specified spacing. Builders sometimes frame the header and kings as an assembly on the deck before standing the wall but forget to add the required nail count at each connection point. Review the nailing schedule during rough framing inspection because missing nails at header connections are a commonly cited deficiency that is straightforward to prevent with a pre-inspection review of the nailing pattern.

What Homeowners Get Wrong

Homeowners creating new openings often install a single 2×6 flat header assuming it provides enough support. A single 2×6 on edge provides a fraction of the structural depth of a proper built-up header and is not an acceptable header for any significant opening. Always use the table values — a properly sized header is cheap insurance against structural problems.

Another common mistake is failing to add jack studs when enlarging an existing opening. If an existing door rough opening is widened, the number of jack studs must be rechecked against the table for the new opening width, and additional jacks added if necessary.

Headers for garage door openings are typically the largest prescriptive headers in a residential project. A 16-foot-wide garage door opening may require a triple 2x12 or an engineered header depending on the loads above. When the garage door opening is in a bearing wall with a floor or roof above, verify the header size against the applicable table column. The portal frame provisions of R602.10.6.2 apply specifically to garage door openings in braced wall lines and may require a different header detail than the standard bearing header table.

State and Local Amendments

IRC 2018 header tables are adopted across TX, GA, VA, NC, SC, TN, AL, MS, KY, and MO. In seismic or high-wind areas, the structural plans may call for larger headers than the prescriptive tables to resist in-plane shear forces, particularly for openings in shear walls. The structural engineer's header schedule governs in these cases, superseding the prescriptive tables.

IRC 2021 did not change the header size tables in R602.7. The prescriptive header requirements are essentially unchanged between 2018 and 2021, though 2021 added clarifications to the table footnotes regarding LVL equivalency sizing.

When to Hire a Licensed Contractor

Any time a bearing wall opening is created or enlarged, a licensed framing contractor familiar with header sizing requirements should perform the work. This includes window and door openings in existing homes during renovations. If the opening is in a shear wall or in a building with an engineered framing plan, the engineer's header schedule governs and must be followed exactly. A licensed general contractor should coordinate all structural framing work and the associated framing inspection.

Common Violations Found at Inspection

• Header too small for the opening width and load — especially common in second-story walls where the tributary load is greater than homeowners assume.
• No jack studs (trimmers) under the header — header bearing directly on full-height king stud only, creating point load on a single stud.
• Mixed species in a built-up header without engineering justification.
• Header size based on the wrong table column — using the roof-only table when the wall actually supports a floor above.
• Header not flush with top of wall — requires cripple studs above, which are sometimes omitted, leaving a gap in the wall framing.
• Flat header (laid flat instead of on edge) — this orientation dramatically reduces the header's structural depth and load capacity.
• No spacer in a 2×4-wall built-up header — the header is narrower than the wall, creating a gap at the sheathing edge.

Multiple adjacent openings separated by cripple studs — such as two narrow windows with a short cripple stud section between them — must have headers sized for each individual opening, not a single header spanning the entire combined opening. If the combined span of two adjacent openings exceeds the single-header table values, the two openings must be redesigned to share a single header spanning the full combined opening with properly sized supporting jack studs at each end.