![]() Otherwise, the roof load and external pressures can exert too much weight on the framing. For instance, space the rafters 12 inches apart on-center for a 16-foot span. ![]() However, the actual spacing depends on various factors, notably the rafter span. Joists supporting additional loads should be calculated by a competent person. The ideal spacing for 2×6 rafters is 16 or 24 inches on-center. These span tables make no additional allowance for water tanks or any other additional loads. These span tables are based on the imposed loads given in BS 5268-7.1 and BS 6399-1, with an imposed uniformly distributed load of 0.25kN/m² acting together with a concentrated (point) load of 0.9 kN. Joists are to have minimum end bearing of 40mm. Youd also have to have the attachments to the top plate of the walls adequate to support the. I cant imagine a garage layout that would have a span short enough to make with 2x4s, even sistered. The width of the room isnt whats important so much as the span from support to support. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. I dont think those rafter ties will work for support. SPAN TABLES Span tables can be used to determine the size of a timber member of a particular strength class required for a given span. 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 joists unless proved adequate by specialist calculations. ![]() These span tables do not apply to ties of trussed rafters.Ĭeiling joists may be continuous or made up of shorter lengths joined at intermediate supports such as binders. 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 5268-7.3:1989 Structural use of timber - Section 7.3 Ceiling joists. * Boarding to be fastened on top of ceiling joists with a depth to width ratio greater than 4 Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm)
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