Centres is 300mm then it can only be used at 300mm centres.Ĭost Index is a rough estimate of the order of Joists and Centres, from cheapest to most expensive, based on RRP. Centres" is 600mm then the joist can be used at 300mm, 400mm, 480mm and 600mm centres. Centres" is the maximum centres that this joist can be used for in this application. The number of supports (beams or purlins) affects the allowable span length. Maximum roof slope is 5° for monoslope and 22.5° for pitched roof. Loads are calculated in accordance with Table 3.1 of AS/NZS 1170.1:2002. (ringed in red.) On the right side in the yellow table is the beam design which requires the incoming rafter span that is to be supported by the beam (indicated in the section diagram) and the length of the beam. This is set by the roof use you selected in the previous screen and cannot be modified. Step 3 Continuous rafter 10 increase Table 10. EXAMPLE: A rafter span of 4,80 meters for roof sheeting without a ceiling will require a 38X228 S5 Rafter. This example is a light roof in a low wind zone, so the Low and Medium multiplier of 1.3 can be used. Patio width is no less than 2.1m and length is no less than 3.5m. Step 2 Rafter span multiplier Table 10.1 has span length multipliers for ‘Low and Medium’ and ‘High and Very High’ wind zones. Patio height (hc) must always be less than roof height (h). It is assumed that for "Built-In" joists that the masonry is 100mm wide and for joists "On Hangers" the hanger has a 75mm bottom plate. Average roof height between 3m and 6.5m (3m h 6.5m). House Loading: 0.75kN/m2 Dead Load + 1.5kN/m2 Imposed Load.įlat Loading: 1.15kN/m2 Dead Load + 1.5kN/m2 Imposed Load.ĭeflection Limit: 0.003 x engineering span or 12mm whichever is lesser.
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