With the purlin/bracing installed, the long rafter span would be broken into two shorter spans, thus allowing the rafter to carry additional load.īefore you decide on lumber sizing and span, consult your local building code officials to determine design loads for your area. You can break up a long span of rafters by installing a purlin and bracing on the underside. Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. This chapter contains two roof-ceiling framing systems: wood framing and cold-formed steel framing. When calculating the span of joists or rafters, use the horizontal distance between vertical supports. User note: About this chapter: Chapter 8 addresses the design and construction of roof-ceiling systems. Joist Spacing Species and Grade Douglas Fir-Larch Hem-Fir Southern Pine Spruce-Pine-Fir. The number 1 grade material is more expensive than the #2 grade, but if you can use fewer or smaller number 1 grade joists or rafters in your design, you may actually save money.ĭepending on the availability and cost of various size framing materials, it may be more economical to use larger joists or rafters in your design because you can typically use fewer of them. Code Ceiling Joist Span Tables for a 20 psf Live Load with a 16 in. For example, you can span a #1 grade (no knots) southern yellow pine joist a greater distance than a #2 grade of the same species (with knots). The lengths and sizes of joists vary depending on the species and quality of the lumber used. To calculate maximum spans of additional species of lumber, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.Ĭonsiderations when using the Rafter and Joist Span Tables Contact your local building code officials to determine the building code for your area. Here too, it is difficult to determine whether the span. Weigh all of the elements when designing wood structures. The Southern Building Code Congress, model code has a problem somewhat similar to ICBO's. Some areas have wind and seismic conditions. For example, some localities get large amounts of snow, whereas others get none. Neither SFPA, nor its members, have knowledge of the quality of materials, workmanship or construction methods used on any construction project and, accordingly, do not warrant the technical data, design, or performance of the lumber in completed structures.Before determining the maximum spans for joists and rafters, you must know the load requirements for your region. The conditions under which lumber is used in construction may vary widely, as does the quality of workmanship. The design values contained herein are based on the Southern Pine Inspection Bureau’s Standard Grading Rules for Southern Pine Lumber (2002 edition with supplements) and modified as required by AWC’s National Design Specification® (NDS®) for Wood Construction (2012 edition).Īccordingly, SFPA does not warrant that the design values on which the span tables for Southern Pine lumber contained herein are based are correct, and specifically disclaims any liability for injury or damage resulting from the use of such span tables. SFPA does not grade or test lumber, and accordingly, does not assign design values to Southern Pine lumber. The maximum spans provided herein were determined on the same basis as those in the code-recognized Span Tables for Joists and Rafters(2012 edition) and Wood Structural Design Data (1986 with 1992 revisions), both published by the American Wood Council (AWC). The primary purpose of this publication is to provide a convenient reference for joist and rafter spans for specific grades of Southern Pine lumber. Span Tables for Purlin Supporting Rafters (to BS 5268-7.6) Imposed loads of 0.
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