![]() Where access to the roof is provided in addition to that necessary for cleaning and repair, the imposed uniformly distributed load should be taken as a minimum of 1.50 kN/m². 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 purlins unless proved adequate by specialist calculations. ![]() The imposed load should be calculated in accordance with BS 6399:Part 3:1988 Code of practice for imposed roof loads, as a rule of thumb for altitudes not exceeding 100m you can use a uniformly distributed load of 0.75 kN/m² and for most other areas exceeding 100m but not exceeding 200m you can use 1 kN/m², for parts of Scotland, Pennines, North East England and heights over 200m you will need to refer to BS 6399 Part 3. The calculations used for these span tables are based on rafters having two equal spans. Joists are to have minimum end bearing of 40mm. The first span tab is for roofs where which. Rafters with ceiling not append into rafters, sanding snow load 50 psf, died load 20 psf, flexion limit L/180. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. The span tables with this folio cover the following two project scenarios: Rafters with ceilings not attached to rafters, live load 20 psf, dead load 20 psf, deflection limit L/180. 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. Note: The 140 × 70 mm rafter size permitted to span 2.9 m could also have been used (since 2.9 × 1.1 multipler 3.19 m), but this is not a stock size so was not chosen. This indicates a 190 × 45 mm rafter size. 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. Read the rafter size in the left column of Table 10.1 for the 3.3 m span chosen. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. If insulation is placed on top of the flat roof joists and as such the joists are not fastened to the boarding above, the depth to breadth ratio of the joists should not exceed a ratio of 4 to 1. as a consideration for selection of joists and rafters. 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 5268-7.2:1989 Structural use of timber - Section 7.2 Joists for flat roofs. * Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 TABLE R802.5.Dead load per square metre (in kN/m²) supported by joistsĬentre-to-centre spacing of joists (in mm) The braces shall be spaced not more than 4 feet (1219 mm) on center and the unbraced length of braces shall not exceed 8 feet (2438 mm). SPAN TABLES FOR JOISTS AND RAFTERS 3 AMERICAN FOREST & PAPER ASSOCIATION Table 9.1 Required compression perpendicular to grain design values (F c) in pounds per square inch for simple span joists and rafters with uniform load. Purlins shall be continuous and shall be supported by 2-inch by 4-inch (51 mm by 102 mm) braces installed to bearing walls at a slope not less than 45 degrees from the horizontal. Fasteners shall be located not less than 1 inch from the edge of the panel. Fasteners shall be installed at opposing ends of the wood structural panel. This table is based on 140 mph wind speeds and a 45-foot mean roof height. Purlins shall be sized no less than the required size of the rafters that they support. For SI: 1 inch 25.4 mm, 1 foot 304.8 mm, 1 pound 4.448 N, 1 mile per hour 0.447 m/s. Installation of purlins to reduce the span of rafters is permitted as shown in Figure R802.5.1. North American Spruce-Pine-Fir species onlyĬEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable attics with limited storage, live load = 20 psf, L/Δ = 240) CEILING JOIST SPACING (inches).For other grades and species and for other loading conditions, refer to the AF&PA Span Tables for Joists and Rafters.ĬEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable attics without storage, live load = 10 psf, L/Δ = 240 CEILING JOIST SPACING (inches)Ĭheck sources for availability of lumber in lengths greater than 20 feet.įor SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa. Spans for ceiling joists shall be in accordance with Tables R802.4(1) and R802.4(2). ![]()
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