Does The Radiant Heat Barrier Harm My Roof?
October 12, 2011
Remembering some things we learned in science can be dangerous when we don't see the entire picture or understand all the concepts. For instance, we consider reflected heat from a mirror to be extremely hot, and if we suppose the same thing happens with radiant heat from our attic, we might have concerns about how much damage we are doing to the roofing materials by using foil in our attics.
Many people have already had these thoughts and extensive testing has been done to determine if there is a cause for concern. Considering that a radiant barrier can decrease the heat in the attic by as much as thirty degrees, it would seem that heat is being returned to the roof, decreasing its lifespan due to extreme temperatures.
How It Works
Consider a black fiberglass roof. It will receive as much as 95% of the incident solar radiation. This makes it hotter than the air temperature around it. A white roof would not get this hot, and we can remember our science teacher telling us that light reflects and dark absorbs. While a black roof might have a shorter lifespan that a lighter one, it can still take a great amount of heat.
The heat from the roof is transferred down into the attic resulting in higher temperatures there than on the outside. The radiant barrier acts like the mirror to reflect heat, not light, away from the attic.
The roof is already as hot as the heat that is passing into the attic without the radiant barrier, so it doesn't experience much change in temperature just because the attic is rejecting the heat.
No Appreciable Change in Roof Temperatures
Roof temperatures do increase from two to five degrees because of the radiant barrier, but that produces no measurable change in the performance of the roof or how long it will remain in good condition. No roofing material supplier reduces the product warranty based on a radiant heat barrier in the attic.
Tests such as one conducted by the Florida Solar Energy Center have shown conclusively that attic radiant barriers reduce energy consumption and there is no indication that roofing materials are damaged by them.
It's rather clear that radiant heat barriers provide more positive results than negative.