The 12' x 20' x 8'6" Round Greenhouse is generously sized and engineered to be strong and durable. The three-layer laminated polyethylene cover is UV-protected to resist damage from the suns rays and comes in a 200 gram 12 x 12 crossover weave for durability. Excellent ventilation is another valuable feature of Canopies and Tarps Round Greenhouse. The cross-side ventilation and upper zipper screened vent gives you excellent climate control and promotes air circulation. Three-piece construction features a cover, vented end panel and door panel. The door panel has two zippered vents for easy removal and installation. The flex-frame design consists of galvanized 11/2" O.D. 16 gauge (.059") steel with inside slip-fit joint fittings 14 gauge (.078"). The supportive and strong Weatherguard Round Greenhouse has 4' on-center arches and 5 horizontal purlins for structural support.