Roof Curb For Fan Base Size 30 in Curb Height 12 in Curb Inside Width 25 1/2 in Curb Outside Width 28 1/2 in Material Steel Standards UL 705 For Use With 30 in Square Base Adjustability Fixed Ventilation Type Nonventilated Application General Exhaust Curb Inside Length 25.5 Curb Outside Length 28 1/2 in Curb Shape Square Damper Tray Size 23 in x 23 in Features Flashing Flange One Welded Corner Wood Nailer Finish Galvanized Flashing Flange Width 2 in