Span Calc 2.14.13

The American Wood Council (AWC) Span Calculator for Wood Joists and Rafters (Span Calc) is a tool that performs calculations for a wide range of softwood and hardwood lumber species and grades according to the 2018 National Design Specification® (NDS®) for Wood Construction. This calculator provides accurate joist and rafter spans for various loading conditions, allowing users to compare different species and grades effectively.

Endorsed by the Softwood Lumber Board, this calculator determines the maximum horizontal spans for joists and rafters under specific assumptions and conditions:

• Joists and rafters are positioned to support vertical loads on the narrow face, leading to strong-axis bending.
• At least three parallel joists or rafters are spaced no more than 24 inches on-center, with appropriate sheathing on the compression edge of each.
• Single-span joists and rafters with proper support at each end are considered; however, cantilevered, multiple-span, or spliced elements are not covered.
• Minimum bearing lengths are defined by building codes and should be adhered to in the absence of calculated values.
• Load combinations considered include dead load plus live load, dead load plus snow load, or dead load plus roof live load. Wind and seismic loads are not addressed.
• Buildings in regions with high ground snow loads should follow accepted engineering practices rather than rely solely on prescriptive provisions.

While meticulous efforts have been taken to ensure the accuracy of the data and relevance to industry standards, neither the American Wood Council nor its affiliates assume liability for any design decisions based on this Span Calculator. Users are fully responsible for any outcomes resulting from utilizing this tool.