Key provisions of the 2009 USEC and changes from the 2006 edition include: • Comprehensively covers solar thermal systems and photovoltaic systems • Allows the installation of single wall heat exchangers • Requires access to solar collector and its components for maintenance and repair purposes • Provides protection requirements for freezing temperatures, water hammer, rodents, corrosion, ultraviolet radiation, decay and termites • Waterproofing requirements when solar collector is installed on a building structure for the prevention