The International Residential Code (IRC) specifies minimum header sizes for every window, door, and garage door opening in a wood-frame wall. Getting the header right is critical—an undersized header can deflect, crack drywall, and in extreme cases, compromise the structural integrity of the wall. This guide explains IRC header sizing rules so you can verify the results from the framing calculator above against the code.
A header is the horizontal beam that spans a wall opening and transfers the load from above—rafters, floor joists, or the roof—around the opening and down through the jack studs (trimmers) into the foundation. Without an adequate header, the weight above the opening would have no path to the ground and the opening would sag or fail over time.
IRC Section R602.7 specifies header sizes based on opening width, wall type (2×4 or 2×6), snow load, building width, and the number of floors above the header. The header size chart on this page shows simplified minimum sizes for exterior bearing walls carrying roof and ceiling loads only. For floor loads, two-story homes, high snow loads, or unusual spans, consult a licensed structural engineer.
Built-up headers: Small roof-only openings can use a built-up (2) 2×4 header. Deeper spans step up to (2) 2×6, (2) 2×8, (2) 2×10, or larger assemblies. In 2×6 walls, spacers or insulation are commonly used so the assembly matches wall thickness.
Jack stud (trimmer) requirements: IRC header tables also specify the required number of jack studs based on span and load case. The jack studs bear directly on the bottom plate and transfer all header load to the foundation, so verify the required count with your local code table for large or heavily loaded openings.
LVL and engineered lumber: When openings exceed 10 feet, the IRC generally requires engineered lumber (LVL, PSL, or LSL) or a site-built box beam designed by a structural engineer. Engineered lumber has published load tables that specify the allowable span for each beam size. Always obtain and submit the manufacturer's span table to your building department with your permit application.
Local amendments: Many cities and counties adopt the IRC with local amendments that require larger headers than the base code. Check with your local building department before purchasing header lumber. The sizes in the reference table on this page represent national IRC minimums and may not satisfy your local jurisdiction.
Minimum roof/ceiling-only header sizes for exterior load-bearing walls (IRC R602.7). Use the header load case selector for walls carrying a floor above. Always check local codes—snow loads, building width, and local amendments can require larger headers.
| Opening Width | Non-bearing Wall | Exterior Bearing Header | Notes |
|---|---|---|---|
| Up to 3'-0" | 2×4 on flat | (2) 2×4 | Commonly equivalent to a 4×4 built-up header depth |
| 3'-0" to 5'-0" | 2×4 on flat | (2) 2×6 | Use rough opening width as the span |
| 5'-0" to 7'-0" | 2×4 on flat | (2) 2×8 | Select the matching floor load case before estimating |
| 7'-0" to 8'-0" | 2×4 on flat | (2) 2×10 | Roof/ceiling-only simplified table |
| 8'-0" to 10'-0" | 2×6 on flat | (3) 2×10 | Confirm jack-stud and bearing requirements locally |
| 10'-0" to 12'-0" | 2×6 on flat | (3) 2×12 | Large spans may need engineered review |
| Over 12'-0" | Engineered lumber (LVL/PSL/LSL) — consult a structural engineer | ||