IronRidge (ironridge.com) expanded its line of rails for PV module roof mounts. There are several models, each for a specific design load. The XR10 is the lightest and is for systems installed in locations that receive little or no snow. It can accommodate 6-foot rail spans (the distance between supports). The XR100 is designed for a range of snow and wind loads, with a span capability of 8 feet. The heavyweight XR1000, for extreme climates and high snow and wind loads, can span up to 12 feet. The IronRidge website offers detailed load and span tables.