Used with RVB, RVD and HVD roof ventilators. For all types of roof construction - for flat, single slope or ridge style roofs. Galvanized steel construction. 1-1/2" insulation thickness, 3 pound density. Low silhouette 8" height overall. Back draft damper consists of a ceiling shutter and built up roof curb. Shutter mounts beneath fan housing to provide an additional weather seal.