Beam span maximums are based on a maximum. Fewer posts on upper-level decks are typically more desirable to the occupants and this drives the use of larger framing materials for longer spans. 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. The span of a beam is dependent on a few variables: The grade and species of lumber, size of lumber and the load it carries. Builders find effi-ciencies in using a single piece during construction. Because I-joists are manufac-tured in long lengths, a single continuous joist is often used to span the width of the house. You can break up a long span of rafters by installing a purlin and bracing on the underside. For residential spans, I-joist depths from 91/2 to 16 inches typically are used. When calculating the span of joists or rafters, use the horizontal distance between vertical supports. 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. 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. Problems that naturally occur as sawn lumber dries twisting, splitting, checking, crowning and warping are greatly reduced. 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 2 Introduction LPSolidStart Laminated Veneer Lumber (LVL) is a vast improvement over traditional lumber. Contact your local building code officials to determine the building code for your area. Weigh all of the elements when designing wood structures. Roof 0.4 kPa Dead Loads Span/300 or 20mm 1200mm for sheet roofs Live Load 0.25 kPa Live loads Span/250 330mm for tile roofs 1.1 kN Wind load Span/150 Snow Load 0. ![]() ![]() Some areas have wind and seismic conditions. For example, some localities get large amounts of snow, whereas others get none. Before determining the maximum spans for joists and rafters, you must know the load requirements for your region. The span tables and construction details contained in this document have been developed primarily for domestic/residential applications in accordance with the principles and intent of NZS3604:2011 Timber Framed Buildings NZS3603:1993.
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