Over the last two decades, the roofing industry has undergone some major changes, one of which is a growing recognition of the value of roof space other than keeping occupants warm and dry. Two veteran roofing professionals share their thoughts on the changes that have been, and where they see the industry heading in this 'black arts' segment of On The Roof With... Ed Jarger, American Hydrotech and John Robinson, Sika Sarnafil.