The term “radiant barrier” may sound like something out of a 1950s science fiction movie, but it’s a real alternative to conventional home insulation that can save energy and money.
Q. What is a radiant barrier?
A. Think of aluminum foil. Although that may seem like a simplification, it’s actually a fairly accurate description.
The Energy Efficiency and Renewable Energy Network, part of the U.S. Department of Energy, says: “Radiant barriers can be anything that is very reflective but still has a very low emissivity.”
Radiant barriers can look very much like aluminum foil. They can come in the form of roof sheathing with a radiant barrier laminate, rolled foil, metal shingles, as chips mixed with cellulose, and even as a paint or spray.
They can be found through some insulation companies, but your best bet to get a wide selection of such companies is on the Internet. Do a computer search under “radiant heat barriers.”
You’ll find a number of companies that specialize in their sale.
Installation can be done by professionals or as a do-it-yourself project.
For the most part, radiant barriers are installed in the attic or attic crawlspaces of homes or as roof sheathing, but some are also installed in walls.
Q. How much energy can be saved by installing a radiant barrier?
A. According to the Energy Department, a radiant barrier can cut as much as 90 percent of the radiant heat from entering the interior of the home, depending on the type of barrier used and the climate.
Some radiant-barrier manufacturers claim as much as a 97 percent reduction in heat gain.
Homes in warmer regions of the country will save more than homes in cooler areas.
Computer studies conducted in the development of the Florida Model Energy Code indicate that a typical attic radiant barrier installed in a Florida home will offer a six- to seven-year simple payback and a 15 percent to 19 percent return on investment.
Q. How do radiant barriers work?
A. When the sun hits your home’s roof, it comes primarily in the form of radiant energy, or heat.
That heat is conducted through the roof and some walls that face the sun and into the home.
A radiant barrier that’s used in the form of roof sheathing applied to the underside of the roof or between the studs in walls that face the sun prevents all but a little of the heat from passing through.
Q. What characteristics should you look for when considering a radiant barrier?
A. The Energy Department says that most radiant barrier materials on the market today have about the same emissivity values. (Emissivity is an industry term meaning how much heat is allowed to pass through a material.)
Because the emissivity numbers are pretty much the same, characteristics such as strength, flammability and cost should be considered when deciding which radiant barrier to buy and install.
Perhaps the easiest types of radiant barriers to install in an existing home are the rolled-foil or bundled types and chips.
In a new home, these types of radiant barriers will also do well, but you also may want to consider roof sheathing with a radiant barrier attached on one side.
Regardless of which product you choose, its resistance to tearing–especially in the rolled-foil or bundle types–is important, especially for a do-it-yourself installation.
One way to judge this is simply to get a sample of a barrier and tear it by hand.
If it rips easily at the fastening points, it could be a very tricky installation. You may want to try different brands with this test.
All should tear, so you’ll have to judge which is the strongest.
Two types of radiant barriers–foil or bundle types–are cited by the Department of Energy as usually stronger than others.
One is of a mesh laminated between two sheets of foil. The other has a bubble pack, the sort of thing you find in packing.
You should also check the flammability rating of each type of radiant barrier. Choose one that has a Uniform Building Code Class I, or National Fire Protection Association Class A, flammability rating.
A special caution when it comes to installing a radiant barrier: Experts in the radiant-barrier industry and in government strongly suggest you not spread a radiant-barrier foil- or bundle-type directly on top of your attic or crawlspace flooring for two reasons.
First, in all weather, dust will gather on top of the barrier greatly reducing its effectiveness over time.
Second, in cold weather, a radiant barrier on top of attic floor insulation may also trap moisture in the fiber insulation.
If you want to install an attic or crawlspace radiant barrier, the sprayed chips–mixed with cellulose–would be better.
Foil in homeowner’s attic cuts temperature, electric bill
Jerry Eastman of Mission Viejo, Calif., may already have done a great deal that the rest of us are trying to do in saving energy around our homes. He wrote to me to explain how he did it:
“I have just about completed a project on my house using radiant barrier aluminum foil, and it did indeed reduce my attic temperature about 50 degrees. However, to optimize the reduction, I did it a little differently than you described in your articles.
“It all started when I had to figure out how to reduce our electric bill from over $200 to around $100. After installing a number of energy-saving devices, last month’s bill was about $88.
“I had installed two gable vents and two roof vents, but the temperature in the attic was still around 140 to 150 degrees. Our goal was to reduce the attic temperature to 90 to 100 degrees. Thanks to the Internet … I quickly learned a few principles about radiant energy.
“Radiant barriers need at least a half-inch of air space on the barrier side [between the radiant barrier and whatever it’s attached to] in order to reflect back the radiant energy to achieve 97 [percent radiant energy reduction]. If there isn’t that half-inch space, the foil becomes a conductor to the surface it’s touching or attached to and substantially reduces effectiveness.
“We installed a double-sided perforated foil [to prevent moisture trapping] on the underside of the rafters to form both a radiant and a moisture barrier. … The perforations are so small they can only be seen by holding it to the light. … We [also] installed ridge vent shingles the full length of the roof ridge and continuous venting on the eaves.
“We then installed the same double-sided perforated foil on the top of the ceiling joists over the fiberglass insulation to prevent heat absorption into the insulation.
“The foil dramatically reduces a buildup [of heat], and our living space is much cooler in the late afternoon and evening. We’re hoping that in the winter, the ceiling foil will also retard heat loss from the living space to the attic, too.
“The total cost of the foil was about $300 for 3,000 square feet of rolled foil [about double that of insulation]. The vent shingles were just over $200 for 60 lineal feet. Materials to the eaves modification totaled about $40 for the lumber and screening.
— Knight Ridder/Tribune
5 generic barrier materials that are on the market
There are many types of radiant barrier materials on the market, and more are being developed as radiant barriers become more widely used, says the Florida Solar Energy Center.
Here are five generic types that are the most common as described by the center:
– Single-sided foil (one foil side) with another material backing such as kraft paper or polypropylene. Some products are further strengthened by fiber webbing sandwiched between foil and backing. The strength of the backing material is important since unreinforced foil tears very easily.
– Foil-faced roof-sheathing materials that come from the manufacturer with a foil facing adhered to one side of the sheathing.
– Foil-faced insulation. The insulating material may be polyisocyanurate, polyethelene “air-bubble” packing or other materials that impede heat conduction.
– Double-sided foil with reinforcement between the foil layers. Reinforcement may be cardboard, kraft paper, Mylar or fiber webbing.
– Multilayered foil systems. When fully extended and installed so that the foil layers do not touch, these products also form insulating air spaces.
– Radiant-barrier “chips” are also manufactured and sold. This product is slightly different from a conventional sheet-type radiant barrier in that the chips, which are blown onto the floor of the attic, typically to a depth of 3 or more inches, act as a multilayer product with many trapped air pockets. These air pockets cause this product to function somewhat like traditional fibrous insulation products. Even though this product may collect dust on its uppermost layer, the remaining layers and air spaces work to significantly reduce heat transfer.
Here are two sources on radiant barriers:
– Florida Solar Energy Center. Phone: 321-638-1000. Visit www.fsec.ucf.edu.
– Reflective Insulation Manufacturers Association. Phone: or 800-279-4123. Visit www.rima.net.
— Knight Ridder/Tribune
