Radiant Barrier - Installed the Right Way
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 within a material or assembly to a colder location, like the way a spoon placed in a hot cup of coffee conducts heat through its handle to your hand. Heat transfer by convection occurs when a liquid or gas — air, for example — is heated, becomes less dense, and rises. As the liquid or gas cools, it becomes denser and falls. Radiant heat travels in a straight line away from any surface and heats anything solid that absorbs its energy.
Most common insulation materials work by slowing conductive heat flow and — to a lesser extent — convective heat flow. Radiant barriers and reflective insulation systems work by reducing radiant heat gain. To be effective, the reflective surface must face an air space. Dust accumulation on the reflective surface will reduce its reflective capability. The radiant barrier should be installed in a manner to minimize dust accumulation on the reflective surface.
When the sun heats a roof, it is primarily the sun’s radiant energy that makes the roof hot. Much of this heat travels by conduction through the roofing materials to the attic side of the roof. The hot roof material then radiates its gained heat energy onto the cooler attic surfaces, including the air ducts and the attic floor. A radiant barrier reduces the radiant heat transfer from the underside of the roof to the other surfaces in the attic.
A radiant barrier works best when it is perpendicular to the radiant energy striking it. Also, the greater the temperature difference between the sides of the radiant barrier material, the greater the benefits that a radiant barrier can offer.
Radiant barriers are more effective in hot climates than in cool climates, especially when cooling air ducts are located in the attic. Some studies show that radiant barriers can reduce cooling costs 5% to 10% when used in a warm, sunny climate. The reduced heat gain may even allow for a smaller air conditioning system. In cool climates, however, it’s usually more cost-effective to install more thermal insulation rather than to add a radiant barrier.
Types of Radiant Barriers
A radiant barrier’s effectiveness depends on proper installation. So, it’s best to use a certified installer. We provide Installer referrals upon request. If you choose to do the installation yourself, carefully study and follow the manufacturer’s instructions and safety precautions, and check your local building and fire codes.
It’s easier to incorporate radiant barriers into a new home, but you can also install them in an existing home, especially if it has an open attic. In a new house, an installer typically drapes a rolled-foil radiant barrier foil-face down between the roof rafters to minimize dust accumulation on the reflective faces (double-faced radiant barriers are available). This is generally done just before the roof sheathing goes on, but can be done afterwards from inside the attic by stapling the material to the bottom of the rafters.
When installing a foil-type barrier, it’s important to allow the material to “droop” between the attachment points to make at least a 1.0 inch (2.5 cm) air space between it and the bottom of the roof.
Perforated Radiant Barriers can also be used as a house wrap, moisture barrier, and vapor barrier, increasing the thermal resistance of your home’s walls.
Solid versions of Radiant Barrier can be used as a roofing underlayment.