Commercial flat roofing originally started with 4 plies of felt paper and mopped with pitch approximately 500 degrees and surface was ladled pitch with gravel surface and that was called a tar and gravel roof. 

   Later technology in commercial roofing was 4 plies of asphalt felt paper mopped with hot asphalt approximately 560 degrees and then ladled surface with hot asphalt and that was a asphalt bald roof.  The life expectancy of these roofs was approximately 10 years if properly maintained.    

   With today's advanced technology we have been using commercial rubber roofing .040 to .060 gauge with various underlayment & special fasteners.  With Pratt & Son all workers are factory trained & certified to install commercial rubber roofing.  You can be assured it will be the last roof you would have to do.