According to the Metal Construction Association's technical document Qualifying Snow Retention Systems for Metal Roofing, a snow guard system, is a series of unitized snow-guard devices or continuous assemblies installed for the purpose of retaining snow on a roof to allow the snow to evacuate slowly via thaw and sublimation rather than suddenly and unexpectedly via rooftop avalanche. Installing a snow retention system (snow guards) helps preserve your metal roof, encouraging snowmelt to exit the roof in a more controlled manner.