![]() ![]() Rafters are to have minimum end bearing of 35mm. ![]() Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. Timber to be covered, these span tables do not apply to timber which is fully exposed to the elements. Holes and notches cannot be drilled or cut into the rafters unless proved adequate by specialist calculations. The calculations on which these span tables are based conservatively assume that the rafters are not continuous over the purlins, but they can be continuous over the supporting purlin if required. These span tables are based on the assumption that the tiling battens fastened to the top of the rafters will provide adequate lateral restraint and also ensure that lateral loads are distributed. It is also assumed ceiling joists will be used to transmit the horizontal component of thrust occurring at eaves level to complementary rafters. These span tables only apply to roof systems with four or more rafters. These span tables do not apply to trussed rafter roofs. The dead loads shown at the top of span table above do not include the self weight of the rafters, however, the rafter self weights are included (in addition to the dead loads) in the calculations used to determine permissble clear spans. The allowable clear spans have been calculated in accordance with BS 5268-2:2002 Structural use of timber - Part 2: Code of practice for permissible stress design, materials and workmanship and BS 5268-7.5:1990 Structural use of timber - Section 7.5 Domestic rafters. ![]() Those using this Span Calculator assume all liability from its use.Dead load per square metre (in kN/m²) supported by raftersĬentre-to-centre spacing of rafters (in mm) 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, Anthony Forest Products Company does not assume any responsibility for any particular design prepared from this Span Calculator application. 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. The Span Calculator does not address wind load or seismic load. 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). Consult the local building code for specific requirements. These minimum bearing lengths are to be used in the absence of calculated bearing lengths. 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. ![]() The Span Calculator does not address cantilevered joists and rafters, multiple-span joists and rafters, or spliced joists and rafters. Joists and rafters are single-span with adequate structural support at each end. 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. thick) face of the member, resulting in strong-axis bending. 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. A "grade/size options" calculator allows selection of multiple grades/sizes for comparison purposes when a span is inserted. The Anthony Lumber Span Calculator (Span Calculator) for Wood Joists and Rafters performs calculations for four species and numerous grades of commercially available softwood lumber as found in the "2012 National Design Specification (NDS) for Wood Construction Supplement: Design Values for Wood Construction with the March 2013 Addendum." Joists and rafter spans for common loading conditions can be determined. ![]()
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