![]() ![]() It should be noted that other species are also tested, we’ve chosen the four species identified in the IRC which are most commonly used in construction. The lumber species most commonly used in construction are Southern Pine (SP), Douglas Fir-Larch (DF-L), Hemlock-Fir (Hem-Fir), and Spruce-Pine-Fir (SPF), while #2 is the most common grade used. The IRC and the American and Canadian Wood Councils test and publish tables and information on maximum structural loads, spans, and standards for different species and grades of wood materials and products. Most lumber yards, however, carry a variety of construction lumber and can order in different species, usually at premium prices. The further it is shipped, the greater the costs. The species of lumber available in your area commonly is what grows within inexpensive shipping distances. Before finalizing structural plans or beginning to build, it is best to check with your local Building Department or a Structural Engineer. It is updated every 3 years, most recently in 2021, and identifies the maximum safe loads and spans for beams, joists, and rafters in an effort to minimize or negate structural failure and human injury or death. The International Residential Building Code (IRC) is used in most of North America as a guide for National, State, Provincial, and local codes. Additionally, the span of joists and rafters is affected by the spacing, typically 12”, 16”, 19-1/2”, or 24” between each other. Quite often, the distance a beam can span is also determined by the spacing of joists or rafters it will support, and vice versa. The distance a joist, rafter, or beam can span depends on the wood species, grade of lumber, loads, and how they are used. Maximum Spans for Joists, Rafters and Beams Chart ![]() Span-by-Span: a term used to identify construction methods for erecting bridges or other large structures requiring multiple long spans often of precast, prefabricated or pre assembled components.įree Span: typically, another term for span, it is the free or unsupported space provided between the supports of a structural component. Long Span: identifies a construction method that typically results in buildings with unobstructed support free spaces greater than 100-feet, such as factories, warehouses, stores, sports arenas, and barns. The bean is multi-spanned, as is the floor being supported. For example, a beam carrying a floor being supported at the ends and with equidistance intermediate posts along its length. Multi-Span: commonly refers to a structural member spanning across multiple supports to minimize bending stresses. Single Span: means the structural member – beam, joist, floor, slab, or rafter – is only supported, pinned, or fixed at its ends. Don’t let them confuse you, they are just ways to identify unique aspects of different structural spans. You may come across the terms single span, multi-span, long span, and even span-by-span in construction. It typically is used when identifying the free or unsupported distance of a beam, joist, slab, floor, header, or rafter between structural supports such as posts, walls, or beams. It refers to the distance, gap, or space between supports that carry the structural piece. In the construction industry, span is the term used to identify the unsupported distance a structural member or component traverses or bridges between supports.
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