A gallon over a big enough area, with a roof that's dark, in 90+degree ambient temperature and direct sun... evaporates within a few minutes. Sometimes < 1 minute by visual inspection, anyway.
re: "doing any good", yes, that's hard to say. The ROI may not be for years, if ever. It was as much a "I have an idea,let's see it through" project as a real money saver.
The attic is insulated, and with a radiant barrier, to boot.
Yeah, a dark asphalt roof and direct sun would do it, as I've observe in my parents' house in Houston. You're also right the the ROI is probably zero or negative since your attic is insulated and has a radiant barrier so the temperature of the roof itself is close to irrelevant.
re: "doing any good", yes, that's hard to say. The ROI may not be for years, if ever. It was as much a "I have an idea,let's see it through" project as a real money saver.
The attic is insulated, and with a radiant barrier, to boot.