[Odin]

Originally Posted by Geonerd

Bare metal, be it aluminum foil, tin, or whatever, do not do well. While they do reflect a lot of heat, they also tend to be very poor radiators. The metal gets hot, and that heat works its way down into the house. Most of the 'cool roof' elastometric coatings are designed to be both highly reflective AND highly emisive. I live in Aridzona, in an old mobile home. The metal roof's original white paint had largely worn away, leaving bare, fairly bright, 'tin' in most places. Painting this with two thin layers of generic cool goop made a vast difference, reducing my summer cooling bill by ~50%. The roof itself is thin, without much insulation, so the 50% is probably a best-case situation. Now, if I can only do something about the poorly insulated walls...

Save the aluminum foil, it's too valuable as an anti-mind control device to waste on the roof! Get decent paint or cough the $ for light colored cool-roof tiles.

seems like you would be better just covering your roof with expanding foam or styrofoam sheeting