"mike" wrote

If your inside is 80F and the roof is 160F, that's 80 degrees
differential.
lowering that to 55 differential cuts your heat flow to 69% of what it
was.

To me the water evaporation thing seems wasteful. I had a house where there
was enough space betwen the peaked roof and the ceiling to install a fan
with a thermostat at one end of the attic and a vent on the other end. The
fan came on whenever the temperature in the attic rose above 85. It kept
the indoors to a respectable 72 to 75 whereas before it used to easily rise
to 90+ in the summer.