In this recent demand for saving energy, many people seem to have forgotten about the low-cost and high-efficiency technology that has been raved about in universities, independent testing labs, and architectural publications since the late 1940s: reflective insulation and radiant barriers.
It is common knowledge the traditional mass-insulation products achieve higher insulating values in relation to their thickness. This is because their efficiency comes from their ability to reduce conductive and convective heat, absorbing approximately 90 percent of the radiant heat. If insulation products with smaller dimensional thickness are desired, they come at a greater cost, which can outweigh their space savings. Reflective insulation on the other hand, reflects approximately 95 percent of all radiant heat - the primary mode of heat gain and heat loss - and therefore increases the insulation value of the dead air space or insulation product adjacent to it.
For example, let’s look at a 2-by-4 cathedral ceiling in Miami, or a 2-by-4 floor cavity above a basement in Minneapolis - areas where heat flux would be a significant issue.
Traditionally, the highest insulation level or R value at the lowest cost would be an R-13 batt, but in each of these examples, there would still be considerable radiant heat loss.
Inexpensive solutionsHowever, if you take that same cavity and put in two layers of inexpensive aluminum foil reflective insulation, you’ve blocked 95 percent of radiant heat and just increased the insulation value to an R-16. This is because the heat flow is down, and all the heat flowing down through any air space is radiant heat, not conductive or convective.
Of course, the more radiant heat striking the reflective insulation, the more efficient the system, so if you have a problematic sun-bearing wall, cold radiant-heated floors, or a roof just about anywhere along the Sun Belt, radiant heat poses a greater threat than either conductive or convective heat, and these products can provide the most cost-efficient solution.
In a vented area like an attic, the product works similarly, in that it completely blocks 95 percent of the radiant heat gain or heat loss.
However, due to the ventilation eliminating any dead air spaces, it insulates without actually adding R value. In such a vented application, the product would be referred to as a radiant barrier.
Rather than the heat being absorbed into existing insulation or dead air directly adjacent to it, the radiant heat is reflected out and convective heat is vented out. Significantly less heat is being absorbed into the attic insulation to begin with, so less heat is being stored or retained. The attic no longer has temperatures in excess of 30 to 50 degrees hotter than the ambient air. Instead, the attic temperature will be within just a few degrees of it.
The most common application for a radiant barrier is in a roof structure, either draped over the rafters beneath the roof sheathing, or in some cases even pre-laminated to the bottom of the sheathing. According to the U.S. Department of Energy, the addition of a radiant barrier to a roof system can save up to 17 percent of the total utility bill. Considering the enormous cost of ownership, compared to the price of constructing a building, imagine being able to tell your clients that you can save them two free months of energy every year that they are occupying their home.
Of course, traditional mass insulation batts eventually settle and lose some of their value over time. Reflective insulation and radiant barriers on the other hand, installed in the manner described above, will continue to reflect 95 percent of the radiant heat, giving a consistent savings over the lifetime of the structure - just one more way that these products stand the test of time.
This article was supplied by the Reflective Insulation Manufacturers Association. For reprints of this article, contact Jill DeVries at (248) 244-1726 or e-mail firstname.lastname@example.org.