A green roof is a supplemental roofing system that covers a conventional roof with a layer of vegetation. There are two basic types of green roofs. "Extensive" green roofs are less than six inches deep and are typically 2-4 inches in depth. Their light weight makes them ideal for retrofit projects on older buildings or any structure with limits on the total weight load. Generally, extensive green roofs require minimal maintenance and can thrive with little supplemental irrigation in most temperate climate zones. "Intensive" green roofs are deeper, which allows for more types of plants and increases potential stormwater retention. Heavier and more expensive than extensive green roofs, intensive systems are higher maintenance and require more irrigation. The XeroFlor Green Roof System is extensive. The key component of the Xero Flor system are thin, lightweight, pre-vegetated mats. XeroFlor green roof mats incorporate a proven, textile-based design developed in Germany and improved over decades of ongoing R&D.