In cold climates, where snow and ice are common, an ice-dam protection membrane is recommended on downslope roof perimeters (e.g. eaves), valleys, and around penetrations. (Consult local authorities for building code requirements.)
Dimensions shown are recommended minimums and are intended to be approximate to allow for reasonable tolerances due to field conditions. Diverter flashing should be a minimum of 26 gallon (0.019 inches) pre-finished galvanized or stainless steel, 16-ounce copper or an equivalent longevity non-corrosive sheet metal, or other appropriate material commensurate with the roofing and flashing system. Vertical flange of diverter flashing suggested to be lapped a minimum of 2 inches.
Sheet metal counterflashing may be optional where wall cladding or siding overlaps vertical flange of diverter flashing. Designers should consider specifying the extension of roofing underlayment vertically up wall so it is overlapped by the wall cladding underlayment or air retarder. The profile of specific components, their configuration or sequencing, can vary with the roof system, climatic differences, local building code requirements, and regional or area roofing and flashing practices.