During the summer, the roof heats up by the sun’s radiant energy. Heat then travels through the roofing material through conduction to the attic side of the roof. The hot roof materials radiate this heat to the cooler attic surfaces, such as the floor or air ducts, which can heat up your living space. This puts undue pressure on the air conditioning system, raising the costs of keeping your home cool. Using a radiant barrier can disrupt radiant heat transfer from occurring through your roof, and as such, it can reduce your energy bills by 5-10%. So how does a radiant barrier work?
How Does a Radiant Barrier Work?
Heat transfer occurs in three ways: through convection, conduction, and radiation. Convection is when a liquid or gas, such as air, is heated, becomes less dense and rises. As it cools, it becomes denser, then falls. Conduction is the transference of heat energy through a solid surface, such as putting your hand on a hot pan. You can feel the heat from the pan flowing to your hand. Radiant heat travels in a straight line away from the heat source and heats anything solid that absorbs its energy. If you put your hand over the hot pan, the heat you feel is radiant heat. If you put aluminum foil under your hand which is over the hot pan, it would reflect the heat back to the pan and you would not feel as much heat.
A radiant barrier is that aluminum foil. It is a thin sheet of highly reflective material. It works by reducing the radiant heat from the underside of the hot roof being transferred to the other surfaces in the attic.
Radiant barriers are typically made of aluminum foil because of its low emissivity (the ability to release heat). The foil can be applied to one or both sides of another substance, such as kraft paper, plastic films, oriented strand board, or air infiltration barriers. Some are reinforced with fiber to increase durability and make it easier to handle. Radiant barriers can also be the backing material on insulation.
How is a Radiant Barrier Installed?
Having at least one inch of air space between the roof and radiant barrier is important. Continuing with our pan analogy, if the pan represents the roof of a building and the foil (radiant barrier) is placed directly on the hot pan without any air space between, it becomes conductive heat. You can feel more heat through the foil. By creating air space between the roof and the barrier, you create radiant heat which the foil can reflect back to the roof, away from the living space.
Dust can also be a problem by reducing the reflectivity of the foil. Radiant barriers work best if they are installed in such a way as to reduce dust accumulation. They are typically installed face down, attached to the rafters.
Radiant barriers should not be placed on top of floor insulation as this can possibly trap moisture in the insulation and accumulate dust.
Do you want to know more?
Could you benefit from a radiant barrier? Contact us today for a free certified energy audit to find out.