What Is Radiant Barrier Reflective Insulation?
Radiant barrier insulation is a reflective insulation system that offers a permanent way to reduce energy costs. Radiant barrier insulation systems reflect radiant heat energy instead of trying to absorb it. A pure aluminum radiant barrier reflective insulation is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be. A radiant barrier insulation system is a layer of foil facing an airspace and is installed in the envelope of a building.
Most people are familiar with traditional insulating materials such as fiberglass, cellulose, Styrofoam, and rock wool. These products use their ability to absorb or resist (slow down) convective and conductive heat transfer to insulate (R-value). A third, seldom discussed but dominant form of heat transfer exists: radiant heat transfer. What are the differences among the three forms of heat transfer?
Conductive: Direct contact. If you touch a pot on the stove,
this is conductive heat transfer.
Convective: Steam, moisture. If you put your hand above a
boiling pot, you will feel heat in the form of steam. This is convective heat
transfer.
Radiant: Electromagnetic. Step outside on a sunny day and feel the sun's rays on
your face. You are feeling radiant heat transfer. All objects above absolute
zero (-459.7 degrees F.) emit infrared rays in a straight line in all directions.
A radiant barrier reflects radiant heat energy instead of trying to absorb it. What does this mean in your home or business? During the winter, 50-75% of heat loss through the ceiling/roofing system and 65-80% of heat loss through walls is radiant. In the summer, up to 93% of heat gain is radiant. If you are depending on R-value (resistance) alone to insulate against heat gain and loss, remember that thin layers of fiberglass are virtually transparent to radiant energy and are affected by changes in humidity (moisture levels). A 1-1/2% change in the moisture content of fiberglass insulation will result in a 36% decrease in performance (referenced from HVAC Manual 10.6; McGraw-Hill). A pure aluminum radiant barrier is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be.
Testing and Approvals
- Building Officials and Code Administrators
- International Conference of Building Officials
- Southern Building Code Congress International
- State of
Radiant Barriers and Foil Bubble Reflective Insulation provide many benefits:
- Substantial reduction in fuel costs
- Greater comfort
- Reduction in the amount of investment dollars needed
for heating and cooling equipment
- Improved appearance
Radiant Barriers Provide
- Double-sided 99% pure aluminum
- Reinforced for maximum strength and durability
- 97% Reflectivity
- Puncture and tear resistant
- 0.03 Emissivity
Radiant Barriers Are Safe To Install:
- Non-toxic/Non-carcinogenic
- Does not promote the growth of fungi or bacteria
- Provides no nest support for rodent or insect pests
- Class A / Class 1 Fire Rating
- Meets fire and smoke safety requirements of most
federal, state, and local building codes
- Requires no maintenance
Radiant Barrier products are clean, lightweight and non-toxic; are unaffected by changes in humidity, do not shrink, and once installed require no maintenance.
Radiant Barrier installs in either existing or new construction. It can reduce heating and cooling costs and is appropriate for a wide range of applications.
- State of
Consumers are less concerned about
how energy barriers work than they are about their effect on utility bills.
This is much less than the 97 percent reduction in attic radiant heat flow
because other forms of heat flow contribute to the total cooling (or heating)
load. Data can expect to vary with region. The following data provided by The Tennessee
Valley Authority,
- All the Radiant Barrier configurations yielded sizable
percent savings (17 percent, based on Energy Star Evaluation) and statistically
significant reductions in summer attic heat transfer compared to the consistency
case. Also, as the ambient temperature increases, the savings also
increase.
- The RB on top was the best summer performer. It
consistently showed heat flux reductions compared to the consistency case
of about 40 percent for almost all ambient temperatures and even showed
savings (17 percent) during mild temperature and night summer conditions.
- The RB configurations provide statistically significant
reductions in winter attic heat fluxes in many, but not all, situations.
The percent savings during night hours and during below 35° conditions,
when heating loads are the highest, are usually sizable (from 6 to 23 percent)
and the differences between the RB configurations and the consistency case
are often statistically significant during these conditions.
(Sources:
Much of the heat entering your home comes through the roof. Adding a Radiant Barrier in your attic helps to keep your house cooler in the summer. A Radiant Barrier is ideal to supplement the insulation already in your attic.
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Insulation Choices |
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Attic application with a turbine or gable vent. A 3" gap along the ridge pole and at the base of the rafters (soffit) ensures enough air flow between the Radiant Barrier and the roof deck. This applies to all vent systems other than soffit and ridge. |
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How is Heat Transferred? |
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Good ventilation in
your attic increases your comfort and helps the materials of your house last
longer. |
Attic application with a soffit and ridge vent
system. |
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Frequently Asked Questions
How does Radiant Barrier (RB) work?
Radiant Barrier is unlike mass insulation which only slows down or resists heat transfer. RB reflects heat. Heat always goes cold by natural law - the problem is how to keep the heat in 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 warm 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.
What is the "R" Value of Radiant Barrier?
The "R" value depends on the number and size of the airspaces surrounding the RB and on the direction of the heat flow. Since RB is usually installed on top of existing mass insulation, its R-value is a moot point. It is RB's ability to reflect heat that makes it such an energy saver.
How does RB keep me warmer in the winter?
Just like wrapping a baked potato in aluminum foil keeps a potato warm longer by holding the heat in, covering your attic insulation with RB holds heat in the house. Another analogy would be that RB 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.
OKAY, RB keeps heat in in the winter, how can it keep heat out in the summer?
Just like a space suit, RB 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 RB 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.
What if RB collects dust over a period of time? Will it still work?
This very issue has been studied by research institutes. Most attics don't accumulate enough dust to affect RB's ability to save energy costs. Thousands of homes and structures have had RB installed for as long as ten years or more with no significant accumulation.
Won't my roof get hotter when I have RB in my attic?
No. RB has been used extensively in the south, showing no difference in roof temperatures, as confirmed by field tests.
Do I have to take out my old insulation to put RB in?
No. RB actually makes your present insulation more effective.
Where do you install RB?
RB can be laid over your present insulation like a blanket or stapled under your rafters or crawl space.
What about foil-faced fiberglass? Isn't it just as good as RB?
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 foil surface is of primary importance.
I already have plenty of insulation in my attic. Do I really need RB?
Regardless of how much insulation you have in your attic, adding RB will save on your heating and cooling expense, and keep you much more comfortable. Energy savings for heating and cooling can vary from 17% to 25% depending on a number of factors, including climate, building configuration, materials used, site, family size and lifestyle. Your RB dealer has been trained to evaluate your home or business and advise you of your savings potential.
Has RB been tested by a qualified independent laboratory or government agency?
The
Will dust collecting on the top of the product hurt its effectiveness over a period of time?
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,
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.
Q. Do I need a radiant barrier if my home is already well insulated?
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
"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
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