AWC Span Calc

American Wood Council

About this app

The American Wood Council (AWC) Span Calculator for Wood Joists and Rafters (Span Calc) performs calculations for all species and grades of commercially available softwood and hardwood lumber as found in the 2012 National Design Specification® (NDS®) for Wood Construction Supplement: Design Values for Wood Construction with March 2012 and March 2013 Addenda. Joists and rafter spans for common loading conditions can be determined. A span options calculator allows selection of multiple species and grades for comparison purposes.

Maximum horizontal spans for joists and rafters are calculated based on the following assumptions and conditions:

· Joists and rafters are oriented to support vertical loads applied to the narrow (1.5 in. thick) face of the member, resulting in strong-axis bending.
· At least three joists or rafters are installed parallel to one another and spaced not more than 24 inches on-center, with properly designed sheathing attached on the top (compression) edge of each joist or rafter.
· Joists and rafters are single-span with adequate structural support at each end. The Span Calculator does not address cantilevered joists and rafters, multiple-span joists and rafters, or spliced joists and rafters.
· For joists and rafters, most building codes specify a minimum bearing length of 1.5 inches on wood or metal and not less than 3 inches on masonry or concrete. These minimum bearing lengths are to be used in the absence of calculated bearing lengths. Consult the local building code for specific requirements.
· Joists and rafters carry only combinations of dead load plus live load (D + L), dead load plus snow load (D + S), or dead load plus roof live load (D + Lr). The Span Calculator does not address wind load or seismic load.
· Buildings in regions with ground snow loads greater than 70 psf should not use the prescriptive provisions of the governing building code without approval of the authority having jurisdiction. Buildings in these high snow zones should be designed in accordance with accepted engineering practice.

While every effort has been made to insure the accuracy of the information presented, and special effort has been made to assure that the information reflects the state-of-the-art, neither the American Wood Council nor its members assume any responsibility for any particular design prepared from this Span Calculator application. Those using this Span Calculator assume all liability from its use.

Ratings and reviews

Just used updated version on my Samsung S22 to size some rafters and floor joists. Wow! 5 Stars all day! This is a fantastic app for the building professional. But straight forward enough for anyone to use. Thank You AWC. This is a great app.

Could not use even once. Downloaded, opened, and it froze and almost froze up my phone completely. Using Samsung Note 9 also. Unfortunately I will be uninstalling. Update 7/3/2020 Thank you for responding. I tried the app again and yes, now it appears to be working just fine. It looks to be a very detailed app and I look forward to trying it out again soon. Thank you for responding and resolving the issue. Have a great day.

Never seen an app this slow. It's like every touch starts a request back to the server and freezes the app while it waits for a response. Tip: the functionality of the calculator on the website is the same, but faster since it doesn't do a reload every time you click something, just for the result.

What’s new

FIX : Application error when selecting short penny weight nails