This is an older home in the Bryan area with two detached garages (below).  We are installing shingles over the existing roofs to reduce cost and eliminate debris.  Be aware, this will void the limited lifetime warranty that Owens Corning provides, but these are superior shingles (Duration – 130 MPH wind resistant, algae resistant, wider SureNail strip, and extra thickness/dimension).  This roof will last for well over 30 years.