I agree with you. I can't remember how long it has been since I have seen one even getting replaced.
Here we have the DOE setting standards for ballasted roofs so they can be considered a 'Cool Roof' also along with all the other types of roofs.. This would surely be considered a good thing if it is more energy efficient than a ballasted roof without the coating. However, ( and speaking only for our roof coating) there is absolutely NO WAY we would ever give a warranty for this specific application. Rocks on top of our coating would not phase it's performance in the cold months but would definitrly drop its effectiveness in the hot months.
Spoke to the inventor of our coating yesterday. He has not seen a ballasted roof in at least 20-years.
Anyone have any ideas where they are still used?????