How Radiant
Barrier works
By Reed Sawyer
Is your home too hot in the summertime? Is
your Air Conditioner just not keeping up with
the demands on it…and failing to keep your
house cool?
Do you wish that there was a way to keep your
house cool, save energy, and extend the life of
your air conditioner?
The answer to all three of those questions
is…yes.
How? Science.
Back in the 50’s, NASA developed a top secret
system for protecting astronauts in space from
extreme heat and extreme cold. In space, the
sunny side will have temperatures, from
radiant energy, of over 450 degrees. On the shade side, the temperatures will be around – 250 degrees.
That’s a temperature differential of over 700 degrees. In
order to protect an astronaut, or a rocket, from boiling in
heat, or freezing in cold, NASA developed a surprisingly
simple form of insulation that reflects the radiant energy.
Without it, we couldn’t have won the Space Race. It was a
top secret invention for years.
You have seen this before. When you park your car in the
sun, and grab the reflective sun shield, that’s radiant
barrier. When you see pictures of steel mill workers in
bright shiny gear, that’s reflective barrier. When you see
firefighters entering burning buildings in bright shiny
aluminum suits: radiant barrier. It works.
Here in Florida, we have a problem with the sun. It’s very
bright, and it’s very hot. When the sun shines down on
your roof, here’s what happens:

The sun shines on your roof. If you have a shiny
metal roof, 60% of the radiant energy is reflected away, and only 40% is absorbed. The degree
of reflection is called “Emissivity”. A black asphalt parking lot has an emissivity factor of 1. A
mirror has an emissivity factor of 0. (Guess what your asphalt shingles are made of? That’s
right, asphalt. It is one of the best, and most effect


ive collectors of radiant energy. It works wonderfully up north, where the shingles absorb the
sunlight, and melt the snow. Do we have that problem in Florida? No? Why are we using
asphalt shingles in Florida?) Some radiant energy is reflected. Most of it is absorbed, where it
travels through the shingles and comes into contact with the plywood sheathing.
The plywood sheathing absorbs the radiant energy, it travels to the underside of the plywood
sheathing and radiates that energy.
That radiant energy from the plywood, (Go up into your attic on a sunny day, put your hand on
the plywood sheathing, it’s hot, isn’t it? It’s radiating energy, just like a radiator) radiates
from the plywood, and radiates through your attic, hitting your insulation. Radiant energy is
either reflected or absorbed. Insulation doesn’t reflect, it absorbs energy. Insulation is
measured by “R” value, “R” stands for resistance. As it heats up your attic, the temperature
rises. Early in the morning, it will be close to the outside temperature, roughly 60-65 degrees,
on average. By 10, it might be in the upper nineties. In the afternoon, it can reach
temperatures of 140 degrees, 150 degrees, and up to 160 degrees, according the SECO. (Sumter
Electric Cooperative)

Radiant barrier is
installed on the
underside of the trusses.
(It’s stapled to the
underside.) When
radiant energy hits the
radiant barrier it is
reflected back. That
energy is directed, like a
chimney, up the roof,
where the hot air is
sucked out of the house
by a solar powered vent
fan.

Is it better to have the hot air
inside of your attic, heating up
your insulation and
overpowering your air
conditioner? Or is it better to
reflect and remove that hot air,
so that the inside of your attic
stays within 5 degrees of the outside temperature?
It’s all part of an integrated engineered system that meets Florida building codes. The radiant barrier
reflects heat away from your attic. The solar powered fans remove that heat. Your house is cooler,
because the heat isn’t trapped in your attic.