The Foil vs Paint Question:
There are two basic types of reflective insulation to choose from when you are considering a radiant barrier to install in your attic. You can either staple up a traditional Radiant Barrier Foil to the underside of the roof rafters or you can spray a reflective paint to the underside of the roof decking. In order to evaluate which of these products is right for you, we will look at two different issues: the overall effectiveness of the products and the definition of a true radiant barrier.
How well it works?
The effectiveness of a Radiant Barrier is measured by its emittance value. Simply put, this is how much heat it gives off to the air below. You want the emittance value to be as low as possible. The emittance value of our Radiant Barrier products is 0.05. In other words, it reflects 95% of any incoming radiant heat. At the time of this writting, the best spray on coating comes in at 0.16. Take a look at the chart below (from RIMA) to compare some common brands.
|ARMA FOIL™ radiant barrier||Energy Efficient Solutions, LLC||0.05|
|Lo/Mit-1||Solec-Solar Energy Corp||.23|
|Lo/Mit-2||Solec-Solar Energy Corp||.23|
|Therma-Guard Silver||United Community Services of America||.57|
|Formula A Barrier Coat #85||Hy-Tech||.66|
|Formula B Barrier Coat #85||Hy-Tech||.70|
|Barrier Coat #233||Hy-Tech||.89|
|Radiosity 3000||Green Building Supply||.89|
|HeatShield R-20||Kwik Co.||.90|
In addition most companies that install the spray on paint type products, only apply it to the roof decking and leave the joists unpainted. All of those exposed roof joists will continue to radiate some heat inside the attic. When the foil is stapled to the bottom side of the roof joists, it covers them as well.
Definition of Radiant Barrier:
According to the most standard definition of Radiant Barrier, it is a material that has an emittance value of 0.1 or less. None of the paint products in the chart above, meet this qualification. If someone tells you that they are going to "spray" a Radiant Barrier to the underside of your roof, they are actually using an "Interior Radiation Controll Coating".