BALLASTED STORM WATER RETENTION SYSTEM

摘要

A roof system (10) designed to retain water during storms and release it slowly over a period of time includes a polymeric water impervious membrane (15) covered with a drainage board (16) in turn covered with a water retention mat (18). The water retention mat (18) and drainage board (16) are held in position by ballast (20), preferably gravel. The mat (18) is designed to retain at least about 25% of a one-inch per hour rainfall and release it gradually over 2 to 3 hours, thereby reducing rain runoff during storms and reducing the load on a storm sewer system.