a curb assembly is provided for mounting on a sloped , standing seam metallic roof , in order to provide support for a roof fixture , such as an exhaust fan or skylight . the curb assembly includes a box - like structure mounted atop the roof in surrounding relationship to a roof opening . the curb assembly further includes an underlying , below - roof frame assembly . specialized upper and lower end connection structure serves to securely mount the curb assembly to the metal roof .