Understanding Radiant Barrier Insulation

How does radiant barrier insulation work?
Heat travels using conduction, convection and radiation. Conduction is direct transfer of heat through materials, while convection transfers heat via moving air and radiation transfer heat through space, much like light. Radiant barriers act like a mirror, reflecting thermal radiation.

The sun itself is a source of radiant heat. The sun’s heat is absorbed by the roofing materials which then radiate the heat through the attic space and onto the attic floor. The insulation and ceiling materials absorb this heat and transfer it into the interior of the house by radiation. The radiant barrier will reflect the heat back to the roof where it will radiate back into the atmosphere.

Why are radiant barriers installed alongside other types of insulation?
No matter what it is made of, mass insulation does one thing: It creates a barrier of still air. This stops air flow needed for convection while acting as a physical barrier to conduction. Together with a radiant barrier, all aspects of heat movement are addressed.

Why is the R value of radiant barrier insulation so low?
R value measures the conduction-blocking effectiveness of insulation in relation to wood, for example, a piece of R20 insulation is the equivalent of a 20-inch layer of wood. Some radiant barriers are designed with a thin air space, so they provide R value. However, R value does not take the material’s radiation-blocking ability into account.

How much benefit can I see by having a barrier installed?
Utility costs can be decreased as much as 17 percent in the right conditions. Radiant barriers are effective in keeping heat inside during the winter as well as keeping heat outside during the summer. This makes them ideal for homes in warm climates as well as those in cold climates. This is particularly true for homes with HVAC ductwork installed in the attic since there is a direct route of heat transfer from the attic air. In a house designed to use barrier insulation in the roof and walls, the reduced heat transfer can allow the air conditioner to be downsized by as much as 10 percent, decreasing energy and construction costs.

Doesn’t the heat reflected by the barrier make the roof hot?
Studies have shown that an increase of only a few degrees in roof temperature when a barrier is added. The barrier also reflects heat back into the house, which lets the roof cool down more at night.

What kind of maintenance does radiant barrier insulation require?
As long as the layer stays intact, it will be effective. Dirt and dust can have an impact on the insulation’s reflectivity, but the amount of dust in attic spaces is so low that radiant barriers are practically maintenance free. Unlike mass insulation, it doesn’t depend on air space to insulate, which means it will never pack down and lose its effectiveness.