American Aldes 4" Roof Cap For Flat Roof. Aluminum construction. American ALDES Model RCR round spun aluminum roof caps are ideal vent duct terminations for sloped or flat roof penetrations. The seamless integral roof flashing and weather cap are impervious to water intrusion, and eliminate the need for curbs on most flat roof applications (Optional unit with twelve-inch (12") extension available for applications in high snow-load areas). The "0" temper allaluminum type "1100" construction is highly durable and corrosion resistant. An integral 3-1/2" collar allows for simple duct attachment. The cap also includes an integral bird screen and is removable for duct inspection and cleaning.