Joists are to have minimum end bearing of 40mm. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. Proprietary strutting is to be used in accordance with manufacturers recommendations. Solid timber strutting to be at least 38mm thick and be a minimum of three quarters of the joist depth. Joist spans over 4.5m - provide 2 rows of strutting at third span positions.Joist spans 2.5m to 4.5m - provide strutting at mid-span.Joist spans up to 2.5m - no strutting required.Strutting or blocking between joists is required as follows Holes drilled at the neutral axis (centre line) are not to exceed 0.25 of the depth of a joist and are not to be less than three diameters (centre to centre) apart and are to be located between 0.25 and 0.4 of the span from the support. Notches are not to exceed 0.125 of the depth of the joist and are to be located between 0.07 and 0.25 of the span from the support. Timber to be covered, these span tables do not apply to timber which is fully exposed to the elements. The dead loads shown at the top of span table above do not include the self weight of the joists, however, the joist 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 5268-7.1:1990 Structural use of timber - Section 7.1 Domestic floor joists. Those using this Span Calculator assume all liability from its use.Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm) 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. Buildings in these high snow zones should be designed in accordance with accepted engineering practice. 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. Joists and rafters are oriented to support vertical loads applied to the narrow (1.5 in.Maximum horizontal spans for joists and rafters are calculated based on the following assumptions and conditions: A span options calculator allows selection of multiple species and grades for comparison purposes. Joists and rafter spans for common loading conditions can be determined. 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 2018 National Design Specification® (NDS®) for Wood Construction Supplement: Design Values for Wood Construction.
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