- Q.I have seen many ads for
radiant barriers designed to save energy. Is there any
evidence that these radiant barriers can reduce home
energy costs? If so, in what climates are they most
effective? How should they be installed?
building scientist at the Florida Solar Energy
Center, responds: In cooling climates, radiant
barriers can and do save cooling energy. Testing at
the Florida Solar Energy Center and other
laboratories have consistently shown that a radiant
barrier can reduce the amount of heat entering a
home through the ceiling by 25 to 40 percent. The
amount of energy saved depends on the level of
conventional insulation in the attic. For those
with a thick layer of attic insulation, a 40%
reduction in the small amount of heat coming
through the ceiling is correspondingly small. For
those with minimal attic insulation, on the other
hand, a 40% reduction in heat flow through the
ceiling is a much larger amount.
Two rules of thumb:
- If you have R-30 or better attic
insulation, the payback period for the
installation of a radiant barrier may be long,
although it will save energy.
- In a cooling climate, a house with a
radiant barrier and R-19 attic insulation,
compared to R-19 with no radiant barrier,
should see a reduction in cooling energy
requirements of about 10 to 12 percent.
Radiant barriers are not recommended in
heating-dominated climates. To my knowledge, there
has been no testing of radiant barriers in a
The easiest and cheapest way to install a
radiant barrier in new construction is to install
roof sheathing with a radiant barrier. Several
manufacturers now offer OSB or plywood roof
sheathing with a laminated radiant barrier. A
radiant barrier system can also be installed under
the bottom of the top chord of a roof truss, or to
the bottom edge of rafters. Installing a radiant
barrier on an attic floor is not recommended, since
such barriers easily get dirty, reducing the
performance of the radiant barrier significantly.
For more information, contact the Florida Solar
Energy Center at 407/638-1000.