Ballasted storm water retention system

Abstract

A roof system designed to retain water during storms and release it slowly over a period of time includes a polymeric water impervious membrane covered with a drainage board in turn covered with a water retention mat. The water retention mat and drainage board are held in position by ballast, preferably gravel. The mat 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

1 . A roof system comprising in the following order:
 a roof deck;   a waterproof layer covering said roof deck;   a drainage member providing flow channels covering said waterproof layer;   a moisture retention mat supported by said drainage member; and   ballast covering said moisture retention mat.   
   
   
       2 . The roof system claimed in  claim 1  wherein said drainage member comprises rigid spacers fixed to a water permeable layer. 
   
   
       3 . The roof system claimed in  claim 2  wherein said moisture retention mat comprises a nonwoven polymeric mat. 
   
   
       4 . The roof system claimed in  claim 3  wherein said nonwoven polymeric mat retains at least about 0.2 gallons of water per square foot. 
   
   
       5 . The roof system claimed in  claim 2  wherein said ballast comprises gravel. 
   
   
       6 . The roof system claimed in  claim 1  comprising an insulation layer between said roof deck and said waterproof layer. 
   
   
       7 . The roof system claimed in  claim 1  further comprising a protective mat between said drainage member and said waterproof layer. 
   
   
       8 . The roof system claimed in  claim 3  wherein said waterproof layer comprises a polymeric membrane. 
   
   
       9 . A roof system wherein the outermost three layers consist of ballast covering a water retention matting covering a water drainage member. 
   
   
       10 . A roof system comprising in the following order:
 a roof deck;   a waterproof layer covering said roof deck;   a drainage member providing water flow paths;   a moisture retention mat supported by said drainage member; and   ballast covering said mat.