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Western Energy Savers
Your Low-E InsulationDistributor
530-894-5076
Your Low-E InsulationDistributor
530-894-5076
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What is a thermal radiation barrier (radiant barrier)?
A radiant barrier is a material that prevents the transfer of heat by infrared radiation- a shiny
aluminum foil surface installed in the attic air spaces. The surface’s low emissivity
prevents it from absorbing or emitting long wave radiation. Thus, the heat transfer from the
exterior of the building to the interior is reduced.
Who initiated the usage of radiant barrier?
Dr. Jason Shih, professor of architecture at Louisiana State University, was the first to use
the application of radiant barriers in buildings. He developed a series of tests, which were
conducted under contract with the Florida Solar Energy Center.
Are radiant barriers the same as insulation?
Most people associate insulation with materials that resist convection and conduction heat
flow. Radiant barriers are specifically designed to reflect radiant heat flow, which can be
controlled in a roof system and or house envelope. Radiant barriers and
convection/conduction insulations perform the same basic function of reducing the flow or
heat into or out of a structure but, unlike radiant barriers, insulations are highly absorbent
to the infrared radiation and do nothing to reduce the amount of heat this absorbs into
those materials.
What problems does the use of radiant barriers solve?
When used in the roof, radiant barriers reduce the amount of heat buildup in the attic and
ceiling. The attic air and building materials do not absorb as much heat from the roof as
they would without the radiant barriers. As the sun heats the roof’s surface during the day,
heat is transferred by infrared radiation across the attic air and is absorbed in the cooler
insulation materials and lumber on the attic floor. Radiant barriers halt the radiation
process by preventing the roof from dumping its heat in a downward direction toward the
living space. Since radiant heat flow in a downward direction is more than ninety percent
of the total heat transfer from the underside of the roof decking to the attic floor, radiant
barriers help keep the heat from building up during the daytime hours. Since the structure
has not absorbed as much heat during the day, much less energy is required to cool it
down on demand.
How do radiant barriers affect my utility costs?
In most warm climates, radiant barriers are effective and economical, and they can cut air-
conditioning costs. In air-conditioned buildings, the cooling equipment has a dual
purpose: lowering air temperature and removing moisture. Radiant barriers lower the
amount of cooling required to maintain the temperature and humidity level for which the
house was designed. By reducing the amount of heat absorbed by the house, the cooling
required to keep a house at a comfortable temperature is reduced. When the attic
temperature is close to the outside temperature, the temperature difference can be cut at
least in half. This allows fewer BTU’s of heat transfer through the ceiling to the interior.
Do radiant barriers have an R-value?
R-value is a measure of insulation effectiveness (a measure of resistance to heat flow by
conduction and convection for a given thickness). Because radiant barriers reflect thermal
energy, and their effectiveness is based on surface emissivity, there is no fixed R-value for
the material. Rather, it varies according to the temperature difference from the bottom of
the deck to the attic floor.
Do radiant barriers work during the winter?
Because of the dual function of a low-emissivity surface, the radiant heat transfer from the
attic floor to the cooler roof is retarded. The amount of convection heat loss is greater in
the winter because of the hot surface being lower than the cold roof deck. The heat simply
floats away from the floor of the attic. Heat loss is reduced by not allowing the attic floor to
radiate heat up the cold roof. In colder areas, where snow builds up on the roof, the
radiant barrier slows the snowmelt next to the roof surface by heat from the inside. This
helps to prevent ice damming.
When used in the attic, will a radiant barrier harm the roofing?
When the radiant barrier is installed under the roofing, there is an increase of only two to
three degrees under the shingles, based on the Florida Solar Energy Center testing report
under a contract (FSEC-CR-GS-82 EEA) with Dr. Jason Shih, Director, and Office of
Building Research at LSU. This rise in temperature is insignificant in the roofing is the
difference between light- and dark-colored shingles. Darker roofs are as such thirty
degrees hotter than light roofs.
All information provided by The Office of Building Research at Louisiana State University,
Baton Rouge, LA 70803
And Solar Design Journal/News a publication of Louisiana Solar Design Association (a
non-profit educational organization)
For more information please call (225) 578-4267
A radiant barrier is a material that prevents the transfer of heat by infrared radiation- a shiny
aluminum foil surface installed in the attic air spaces. The surface’s low emissivity
prevents it from absorbing or emitting long wave radiation. Thus, the heat transfer from the
exterior of the building to the interior is reduced.
Who initiated the usage of radiant barrier?
Dr. Jason Shih, professor of architecture at Louisiana State University, was the first to use
the application of radiant barriers in buildings. He developed a series of tests, which were
conducted under contract with the Florida Solar Energy Center.
Are radiant barriers the same as insulation?
Most people associate insulation with materials that resist convection and conduction heat
flow. Radiant barriers are specifically designed to reflect radiant heat flow, which can be
controlled in a roof system and or house envelope. Radiant barriers and
convection/conduction insulations perform the same basic function of reducing the flow or
heat into or out of a structure but, unlike radiant barriers, insulations are highly absorbent
to the infrared radiation and do nothing to reduce the amount of heat this absorbs into
those materials.
What problems does the use of radiant barriers solve?
When used in the roof, radiant barriers reduce the amount of heat buildup in the attic and
ceiling. The attic air and building materials do not absorb as much heat from the roof as
they would without the radiant barriers. As the sun heats the roof’s surface during the day,
heat is transferred by infrared radiation across the attic air and is absorbed in the cooler
insulation materials and lumber on the attic floor. Radiant barriers halt the radiation
process by preventing the roof from dumping its heat in a downward direction toward the
living space. Since radiant heat flow in a downward direction is more than ninety percent
of the total heat transfer from the underside of the roof decking to the attic floor, radiant
barriers help keep the heat from building up during the daytime hours. Since the structure
has not absorbed as much heat during the day, much less energy is required to cool it
down on demand.
How do radiant barriers affect my utility costs?
In most warm climates, radiant barriers are effective and economical, and they can cut air-
conditioning costs. In air-conditioned buildings, the cooling equipment has a dual
purpose: lowering air temperature and removing moisture. Radiant barriers lower the
amount of cooling required to maintain the temperature and humidity level for which the
house was designed. By reducing the amount of heat absorbed by the house, the cooling
required to keep a house at a comfortable temperature is reduced. When the attic
temperature is close to the outside temperature, the temperature difference can be cut at
least in half. This allows fewer BTU’s of heat transfer through the ceiling to the interior.
Do radiant barriers have an R-value?
R-value is a measure of insulation effectiveness (a measure of resistance to heat flow by
conduction and convection for a given thickness). Because radiant barriers reflect thermal
energy, and their effectiveness is based on surface emissivity, there is no fixed R-value for
the material. Rather, it varies according to the temperature difference from the bottom of
the deck to the attic floor.
Do radiant barriers work during the winter?
Because of the dual function of a low-emissivity surface, the radiant heat transfer from the
attic floor to the cooler roof is retarded. The amount of convection heat loss is greater in
the winter because of the hot surface being lower than the cold roof deck. The heat simply
floats away from the floor of the attic. Heat loss is reduced by not allowing the attic floor to
radiate heat up the cold roof. In colder areas, where snow builds up on the roof, the
radiant barrier slows the snowmelt next to the roof surface by heat from the inside. This
helps to prevent ice damming.
When used in the attic, will a radiant barrier harm the roofing?
When the radiant barrier is installed under the roofing, there is an increase of only two to
three degrees under the shingles, based on the Florida Solar Energy Center testing report
under a contract (FSEC-CR-GS-82 EEA) with Dr. Jason Shih, Director, and Office of
Building Research at LSU. This rise in temperature is insignificant in the roofing is the
difference between light- and dark-colored shingles. Darker roofs are as such thirty
degrees hotter than light roofs.
All information provided by The Office of Building Research at Louisiana State University,
Baton Rouge, LA 70803
And Solar Design Journal/News a publication of Louisiana Solar Design Association (a
non-profit educational organization)
For more information please call (225) 578-4267
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