Attics heat up when the sun’s radiant energy heats the shingles. That heat is transferred to the interior attic space through the roofing materials via conduction. That’s unless you install a radiant barrier to reduce attic heat gain. What does this matter? Because, as attic temperatures increase, that heat is transferred to the building below. A radiant barrier lowers heat transfer, keeping attics cooler and lower cooling costs.
How does a radiant barrier work?
Heat travels from a warm area to a cool area by a combination of conduction, convection, and radiation. Heat flows by conduction from a hotter location to a colder location. It’s like the way a spoon placed in a hot cup of coffee conducts heat through its handle to your hand. Radiant heat, on the other hand, travels in a straight line. It goes straight from any surface, heating anything solid that absorbs its energy.
Most insulation works by slowing conductive heat flow. Radiant barriers work by reducing radiant heat gain. To be effective, the reflective surface must face an air space. Dust accumulation on the reflective surface reduces its reflective capability. That’s why a radiant barrier should be installed to minimize dust accumulation on its reflective surface. Make sure yours is installed on rafters and roof decking, never on the attic floor.
The myth of radiant barriers.
Contrary to common legend, radiant barriers were not invented by NASA. They were first created by German businessmen Schmidt and Dykerhoff in 1925. NASA has employed radiant barriers since the days of Apollo. They protect against thermal radiation and for insulation in the fluctuating temperatures of space.
While dispelling myths, color and reflectance of a substance doesn’t add to its efficiency as a radiant barrier. It’s true that radiant barriers significantly reduce cooling costs. But, they’re best used as part of a cohesive building envelope.
Foil radiant barrier
Highly reflective aluminum foil radiant barriers come in two varieties. They come affixed to roof decking. Or, the foil can be added to rafters in an existing roofing system. Foil radiant barriers are best for new construction or when redecking an existing roof. When installing foil, it’s important to allow the material to “droop” between the attachment points to make at least a 1.0 inch air space between it and the bottom of the roof.
Installing foil in an attic is both time consuming. It’s also not 100% effective. Remember, radiant heat travels in a straight line. That means hard-to-reach areas where foil may not reach, become potential radiant heat leaking points.
Spray-on radiant barrier
Similar to radiant barrier insulation foil, radiant barrier sprays work by preventing heat transfer. The difference between radiant barrier foil and LO/MIT radiant barrier spray is that the spray is applied directly to the roof deck, This transforms the roof itself into a heat-resistant material. We recommend LO/MIT since it’s the only one-part, premixed heat reflecting coatings in the market.
You’re not done yet
Properly spraying your roof deck with barrier spray alone greatly reduces the attic temperature by as much as 20-24%. You benefit from instant protection against the sun. But, any radiant barrier is one of three components needed for an energy efficient attic.
For optimal efficiency, your attic needs adequate ventilation and insulation as well. Ventilation, using soffit vents at the base of your roofline and ridge vents at the peak, allows for convective cooling. This way, cool air is drawn in at the bottom, moist, hot air is vented out the top. Insulation, meanwhile, protects living spaces below from accumulated attic heat.