09-26-2010, 03:07 AM
White is by far the best reflector of radiant heat. Silver doesn't work very well as the aluminum in it actually absorbs heat and makes the roof hot. I used the ceramic additive years ago and was not impressed. It may have made some minor difference but not enough to really matter. As far as HPM roofs having a reflective barrier, I don't think it's effective. I have looked at the test that purport to show them reflective a large percentage of radiant heat but that has not been my experience. All of their metals except Mauna Kea White get very hot to the touch. This acts just like a metal radiator radiating heat into the building. White roofs don't get hot.
You can tint some paints but every bit of tint you add decreases the reflectivity of the roof. I know for TPO membrane roofs, a white roof reflects about 95% of radiant heat while the tan reflects only 70%.
Have you considered installing a radiant barrier under the roof somehow? If so, it would need to be separated from the metal roofing by at least 3/4". This is the most cost efficient way to cool a house because it keeps the heat from coming in in the first place. You could tint the roof slightly and add the radiant barrier as a compromise.
You can tint some paints but every bit of tint you add decreases the reflectivity of the roof. I know for TPO membrane roofs, a white roof reflects about 95% of radiant heat while the tan reflects only 70%.
Have you considered installing a radiant barrier under the roof somehow? If so, it would need to be separated from the metal roofing by at least 3/4". This is the most cost efficient way to cool a house because it keeps the heat from coming in in the first place. You could tint the roof slightly and add the radiant barrier as a compromise.