Roof Curb For Fan Base Size 22 in Curb Height 12 in Curb Inside Width 17 1/2 in Curb Outside Width 20 1/2 in Material Steel Standards UL 705 For Use With 22 in Square Base Adjustability Fixed Ventilation Type Nonventilated Application General Exhaust Curb Inside Length 17.5 Curb Outside Length 20 1/2 in Curb Shape Square Damper Tray Size 15 in x 15 in Features Flashing Flange One Welded Corner Wood Nailer Finish Galvanized Flashing Flange Width 2 in