Monticello 4' Extension Kit is specifically designed for the Monticello line of greenhouses. Allows you to grow your greenhouse as your needs grow. Design and installation is simple and takes under 2 hours to assemble. Features an integrated flush base design and dual rain water gutter system. Made using high impact, UV stable 8-mm twin wall polycarbonate walls and roof with heavy duty extruded aluminum framing. Comes with a 2' x 2' roof vent with automatic opener and gutters. 10 year warranty. Made in USA.