The 4-inch GreenGrid Extensive Roof Garden System consists of a 4-inch layer of growth media and drought-tolerant vegetation like sedum that requires little maintenance. It provides benefits like reducing roof temperature extremes and storm water runoff. The system weighs approximately 15 pounds per square foot when wet. The 8-inch GreenGrid Intensive Roof Garden System allows for a wider variety of plants and is intended for public access, requiring irrigation and fertilization for maintenance. It weighs around 28 pounds per square foot when wet. Both systems support plant growth in USDA zones 4 through 8.