Window / Door Header Sizing (IRC R602.7)
Smallest built-up dimension-lumber header (double / triple 2x6-2x12) from tributary load, span, snow, and species.
Example
You enter
- Header clear span (ft) 6
- Tributary width (ft; half the building width) 14
- Ground snow load (psf) 30
- Species and grade SPF_No2
You get
- Member size 2x10
- Plies 2
- Design load on header 630
- Jack (trimmer) studs each end 1
- Bending ok Yes
Details, formula, and sources
With the AWC NDS bending / L-360 deflection check and IRC R602.7.5 jack-stud count.
Tributary uniform load w (plf) = total area load (psf) × supported width (ft); roof = ground snow + 15 psf dead, each floor adds 50 psf. Smallest built-up member with min(L_bending, L_deflection) ≥ span, where Fb is adjusted by load-duration C_D and size factor C_F. Jack studs each end = ceil(end reaction / (F_c-perp × 5.25 in²)).
IRC 2021 (International Residential Code). §R602.7 (headers). AWC NDS-2018 (National Design Specification for Wood Construction). reference design values, load-duration C_D and size factor C_F.
Free read-only access at codes.iccsafe.org. AWC NDS free at awc.org.
Estimate. AHJ and licensed structural engineer govern.
Field names used by the API: header_span_ft, tributary_width_ft, ground_snow_psf, species_grade, member_size, plies, w_plf, jack_studs_each_end, bending_ok
- Load assembly roof = snow (live) + 15 psf dead; each floor above = 40 psf live + 10 psf deadIRC 2021 typical residential
- Load-duration factor C_D 1.15 snow (roof-only) / 1.0 occupancy (floors above)AWC NDS-2018 Table 2.3.2
- Cross-check allowable spans verified against IRC Table R602.7(1) by physics; discrepancies flaggedIRC 2021 Table R602.7(1)