Radiant Barrier is unlike mass insulation which only slows down or resists heat transfer. Radiant Barrier reflects heat. Heat always goes cold by natural law—the problem is how to keep the heat in the winter and how to keep it out in the summer. There are three ways in which heat goes from warm spaces to cold spaces: conduction is direct heat flow through a solid object such as a wall or a ceiling. Convection is heat movement through air, occurring when air is warmed. The heat expands, becoming less dense and rising. Radiation is the movement of heat rays across air spaces from one warm object to a cooler object. The heat we feel from a wood stove or a quartz space heater is radiant heat. All objects and bodies give off radiant heat. Even the insulation in your attic gives off radiant heat to the cold attic space in the winter, and to the living space in the summer. Regular insulation won’t stop radiant heat loss. Radiant heat must be reflected with a radiant barrier.
The “R” value depends on the number and size of the airspaces surrounding the Radiant Barrier and on the direction of the heat flow. Since Radiant Barrier is usually installed on top of existing mass insulation, its R-value is a moot point. It is Radiant Barrier’s ability to reflect heat that makes it such an energy saver.
Just like wrapping a baked potato in aluminum foil keeps a potato warm longer by holding the heat in, covering your attic insulation with Radiant Barrier holds heat in the house. Another analogy would be that Radiant Barrier in the winter works just like a space blanket, which, although very thin and lightweight, holds your body heat in. A thin space blanket can keep you warmer than several heavy blankets.
Just like a space suit, Radiant Barrier reflects the sun’s heat before it can warm up the insulation in your attic. When the insulation stays cooler, your house will stay cooler. It helps to understand how Radiant Barrier will work for you if you think of other things that work in much the same way. Astronauts’ space suits keep body heat and reflect the sun’s heat away. Thermos bottles keep hot things hot and cold things cold. They are almost perfect insulators. The tight seal and air space prohibit heat transfer by conduction and convection. The reflective surfaces inhibit radiation heat transfer. If the bottle starts out hot, it stays hot because very little heat is transferred to the cooler outside. If it starts out cold, it stays cold because very little heat is transferred from the warmer outside.
This very issue has been studied by research institutes. Most attics don’t accumulate enough dust to affect Radiant Barrier’s ability to save energy costs. Thousands of homes and structures have had Radiant Barrier installed for as long as ten years or more with no significant accumulation.
No. Radiant Barrier has been used extensively in the south, showing no difference in roof temperatures, as confirmed by field tests.
No. Radiant Barrier actually makes your present insulation more effective.
Radiant Barrier can be laid over your present insulation like a blanket or stapled under your rafters or crawl space.
No. The foil on the fiberglass is in direct contact with the attic floor. Aluminum foil becomes more conductive when in contact with a solid surface. The air space facing the reflective surface is of primary importance.
Regardless of how much insulation you have in your attic, adding Radiant Barrier will save on your heating and cooling expense, and keep you much more comfortable. Energy savings for heating and cooling can be as much as 17%, depending on a number of factors, including climate, building configuration, materials used, site, family size and lifestyle. Your Radiant Barrier dealer has been trained to evaluate your home or business and advise you of your savings potential.
The Florida Solar Energy Center at Cape Canaveral has tested radiant barriers in both small-scale laboratory and full-scale building models. Their results indicate that radiant barriers provide significant resistance to heat transfer. Current tests conducted by the Tennessee Valley Authority and the University of Mississippi support the findings of the Florida Solar Energy Center. Northeastern Illinois University conducted winter tests in residential and commercial structures using infra-red thermograph photography. The photos showed significant resistance to heat transfer over the regular insulation.
A1 “Aluminum foil exposed in a vertical position since 1929 to the dust and fumes in the Heat Measurements Laboratory, M.I.T. Samples of this foil have been removed from time to time and the emissivity determined. Over a period of 10 years no appreciable change in emissivity was found.” American Society of Heating and Air Conditioning Engineers’ Journal Section, Jan. 1940, Professor Wilkes, M.I.T. A2 “Thin layers of dust readily visible to the eye do not cause very serious lowering in the reflective power. The appearance of the surface is not a reliable guide as to its reflectivity for radiant heat, and foil which appears dark or discolored may have lost little in insulating value if the surface film is thin.” -The National Bureau of Standards, U.S. Dept. of Commerce, Letter Circular - 535.
A1 “Hundreds of samples of aluminum foil have been stored in the laboratory for various periods of time up to 10 years with no visible signs of deterioration.” American Society of Heating & Air Conditioning Engineers’ Journal Section. A2 “Aluminum is highly resistant to the effect of corrosion… Aluminum is constantly being used where it is exposed to weather, salt spray and other conditions, which would adversely affect most metals.” The United States Rubber Co. Booklet, Serving You Through Science, Page 5.
A1 SUMMER: “A radiant barrier system can stop 97 percent of the thermal radiation across an attic space. If it is not stopped, that radiant energy would be absorbed by the ceiling insulation and eventually be transferred to the living space below.” The Solar Collector, Quarterly Newsletter of the Florida Solar Energy Center. “The heat storage capacity of reflective insulation is low. As a result, it does not store heat during summer days, only to pass it on down into the rooms of the house from the attic at night when coolness is most apt to be desired from the point of view of sleeping comfort.” Progressive Architecture, Nov. 1949, Page 76. A2 WINTER: “CONCLUSIONS: Reflective foil retrofitted to fiberglass insulated…buildings is demonstrably effective in reducing heat loss… Installation of foil in uninsulated buildings would show even more pronounced reduction in heat loss.” Effects Of Reflective Foil On Heat Loss in Attic Floors and Metal Building Installations, Northeastern Illinois University, Prof. Charles Shabica, May 20, 1986.