Does Radiant Barrier Cause Roofs And Shingles To Overheat?
The short answer is no. Roofs with a radiant barrier will see temperatures increase by only a few degrees (usually between 2º and 10º degrees Fahrenheit). This slight increase is considered a nominal increase because typical roofing systems are designed to handle temperatures well above the maximum temperature they actually reach in real-world applications. Most shingle manufacturers warranty their product over a radiant barrier and, in fact, some areas require a radiant barrier when doing new construction.
What Determines Roof Temperature?
There are two main variables that will determine the maximum temperature a roof will reach: color and ventilation. First, the roof color is the biggest factor; dark colored roofs can easily be 20ºF+ hotter than light colored roofs. Second, air temperature and wind movement over and under the roof affect the temperature. The roof absorbs radiant heat from the sun, but air flow (either wind or attic ventilation) has a cooling effect on the roof, and helps bring down the overall temperature. The cooler a roof is, the less radiant heat it emits. In theory, if your roof never got any hotter than the outside air temperature, then a radiant barrier would not be needed. This is why homes in complete shade don’t benefit much from installing a radiant barrier.
Based on these variables, every roof will reach a point where the maximum temperature stabilizes. This happens when heat absorbed from the sun and heat being lost due radiation, ventilation and air temperature, all equalize. A typical roof on a hot, sunny day will stabilize between 140º – 180º without a radiant barrier installed beneath it.
Where Does the Reflected Heat Go?
Installing a radiant barrier underneath the roof will cause the roof temperature to increase by a few degrees (usually 2-10º). The heat that would normally be absorbed by the insulation is now being bounced back to the roof deck, and causing the roof to emit more heat upward, rather than both upward and downward. The roof still is gaining and loosing heat; the radiant barrier is basically just directing the (same amount of) heat away from the attic and the attic insulation.
To understand this better, consider a room with one light source (in the form of an unshaded light bulb) hanging in the middle of the room. Under normal circumstances, the bulb sends out light (and heat) in all directions, illuminating the room. Now, add a reflector to the bulb and the light (and most of the heat) is directed downward, below the reflector. The amount of light (and heat) the bulb produces has not changed; what has changed is the direction the light and heat are going. This is the same with a radiant barrier. The amount of heat on a roof hasn’t changed (by much), it’s just that now instead of heat radiating in all directions (upward and downward from the roof) it’s mostly being radiated (forced by the reflective radiant barrier) upward and away from the attic.
Your Roof Will Not “Bake” By Adding a Radiant Barrier
So, adding AtticFoil™ Radiant Barrier to your roof redirects the heat being absorbed by your home and therefore keeps your attic, and ultimately your home, more comfortable and energy efficient. The small increase in your overall roof temperature is not enough to have a significant impact your roof, shingles, or any other part of the roofing assembly.
For more information on the effect of radiant barrier on exterior roofing materials, you can read the technical bulletin published by RIMA here. Below are the details of a little test we did to further prove these facts. Our results were consistent with those of national/government testing.
A view of the inside of the test attic. Three pieces of AtticFoil™ Radiant Barrier Foil insulation are attached to one side with a single strip extending off to the side.
This ia an overlay of thermal image over the regular image. You can clearly see where the foil is stapled up. There is about two feet at the bottom (below top plate of wall over soffits) with no foil and about 18″ from the top due to where the three pieces ended. We also did not put foil over the last rafter bay on the left to show clearly where the foil ends.
This image shows the roof over the radiant barrier measuring 7ºF hotter (the white color represents a hotter temperature) than the area without a radiant barrier (red areas). Typically, the roof temperture over a radiant barrier will increase less than 10ºF which should not have a significant impact on the performance of a roof.
Bottom line: it really does not make a big difference if the roof is light or dark because they both get super hot. Both roofs pass this heat/energy into the home. All homes: light and dark roofs need a radiant barrier.