Processes for making algaecidal roofing granules are disclosed. In one aspect, the disclosure provides a method includes providing composite nanoparticles comprising algaecidal nanoparticles and a carrier material; coating granule cores with the coating material to form a coating layer having an exterior surface; and applying the composite nanoparticles to the exterior surface of the coating layer to provide the algaecidal nanoparticles at exterior surfaces of the algaecidal roofing granules. In another aspect of the disclosure, a method includes dispersing composite nanoparticles in a coating material, the composite nanoparticles including a carrier material and algaecidal nanoparticles, then coating the granule cores with the coating material to form a coating layer; and curing the coating layer, the cured coating layer providing algaecidal nanoparticles at exterior surfaces of the algaecidal roofing granules.