Also known as hoop houses or row covers, the tunnels consist of U-shaped metal or PVC (polyvinyl chloride) ribs draped by thin plastic sheets which are held on by Snap Clamps . They provide shade for sun-sensitive crops, protect tender plants from frost, help control insects and boost yields. Why build hoop houses instead of traditional greenhouses? Primarily because they don’t need artificial heat when temperatures drop. Passive solar heat is enough to protect plants. You ca