Deck Beam and Post Sizing (IRC R507)
Deck beam ply and size, post size (4x4 / 6x6) from an NDS column check, footing size from soil bearing, and the IRC R507.9.1.3 ledger fastener spacing.
Formula and source
Tributary width to beam = joist span / 2; beam load w (plf) = (live + dead) psf × tributary. Smallest built-up beam with min(L_bending, L_deflection) ≥ post spacing. Post axial load = w × post spacing; NDS column capacity = F_c × C_P × A with C_P from F_cE = 0.822 E_min / (le/d)². Footing from soil bearing; ledger fastener spacing from IRC Table R507.9.1.3(1).
IRC 2021 (International Residential Code). §R507 (decks). AWC NDS-2018 (National Design Specification for Wood Construction). reference values; IRC Table R507.9.1.3(1) ledger fasteners.
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