Oct 18, 2025
Wood joist span and spacing depend on size, species, and load. Learn standard spacing, tables, and formulas for floors, rafters, and timber.
Wood joist span and spacing are critical factors in floor and roof construction, determining structural strength, rigidity, and load-bearing capacity. Properly spaced timber joists—whether 2x6, 2x8, or engineered C24 or I-joists—ensure safety, durability, and efficient material usage. This guide provides detailed tables, charts, and formulas to help you calculate joist span, spacing, and size for residential and commercial construction projects.