Home > Stramit Building Products > Commercial Roofing

Longspan® Materials Stramit Longspan® cladding is manufactured from hi-tensile G550 BHP Colorbond® XRW steel or BHP Zincalume® steel. In some locations galvanised and Colorbond XSE steel may be available by arrangement. Colorbond XRW (and XSE) is in accordance with AS2728 - Category 3 and, for the substrate, with AS1397. Zincalume AZ150 and galvanised Z450 conform to AS1397. Stramit has a comprehensive range of Colorbond colours as standard. Refer to the BHP Colorbond 18 colours chart available from Stramit, and ask your nearest Stramit location for colour availability. Sheeting Mass (kg/m2 or roof area) Zincalume Colorbond Galvanised 0.42mm BMT 4.66 4.74 5.07 0.48mm BMT 5.29 5.37 5.70 Spring Curving Stramit Lonspan® cladding can be spring-curved, concave and convex, including curved ridges, provided it is sealed at the apex, and within the recommended limits below: Spring-Curved Radii limits (m) performance restricted restricted by drainage at the rainfall intensities shown bmt (mm) minimum* radius lowest neutral radius 370 mm/hr 220 mm/hr 150mm/hr 0.42 30* 88 78 131 192 0.48 20* 113 78 131 192 * At these radii a maximum support spacing of 1200mm applies, and limit state pressure capacities are reduced by 14% for serviceability and 7% for strength. These reductions apply proportionately, up to the lowest neutral radius. Thermal Expansion All metal roof sheeting is subject to thermal expansion and, where there is a tempurature difference between the sheeting and the structure, this needs to be accommodated. The colour of the sheeting will affect the amount of thermal expansion, and whether the sheet is flat or curved will affect its ability to resist without problems. Sheet lengths should be limited to those shown below. Maximum Sheet Length (m) roof colour light dark Flat 25 17 Spring-curved 20 17 Water Carrying Stramit Longspan® cladding has a superior water-carrying capacity, to most close pitched trapezoidal profiles. This and the decking stiffness enable roof slopes to be as low as 1.5° for many applications. Roof run lengths are the combined lengths of all roof elements contributing to a single pan drainage path. This can include the roof length upstream of a roof penetration that concentrates flow into other pans. The table below gives slopes for 100 year return period rainfall intensity. Minimum Roof Slope (degrees) rainfall intensity Total Roof Run Length (m) 20 25 30 40 50 60 70 80 90 100 110 150 1.5 2.2 3.3 4.6 5.4 7.5 9.5 175 minimum slope 1.5° 1.5 2.0 4.7 6.4 8.3 11 14 200 1.5 2.8 4.6 6.5 9.0 12 15 18 225 1.5 2.2 3.8 6.0 8.5 12 15 19 22 250 1.5 2.8 5.0 7.5 11 15 19 23 275 1.5 1.7 3.6 6.0 9.3 14 18 22 300 1.5 2.0 4.6 7.5 12 16 21 325 1.5 2.7 5.3 9.0 14 19 25 350 1.5 1.9 3.2 6.2 11 16 22 375 1.5 2.4 3.8 7.5 13 18 25 400 1.6 2.7 4.3 8.0 15 20