The usage of Radiant Barriers

Radiant barriers are typically constructed in homes' attics to limit summer heat gain and lower cooling expenses. Instead of absorbing radiant heat, the barriers are made of a highly reflective substance that reflects it. However, they do not inhibit heat conduction like thermal insulating materials.

How They Operate

Combining conduction, convection, and radiation, heat flows from a warm location to a cool area. Heat flows by conduction from a hotter region within a material or assembly to a colder position, similar to how the handle of a spoon immersed in a hot cup of coffee transfers heat to your hand. Convection heat transfer happens when a heated liquid or gas, such as air, becomes less dense and rises. The liquid or gas grows denser and descends as it cools. Radiant heat flows away from any surface in a straight line and warms any material that takes its energy.

Most popular insulating materials function by slowing both conduction and, to a lesser extent, convection heat transfer. Radiant barriers and reflecting insulation reduce radiant heat gain. For the reflecting surface to be effective, it must face an air gap. Dust collection on a reflective surface will diminish the surface's reflectivity. The radiant barrier should be placed such that dust buildup on the reflective surface is minimized.

When the sun heats a roof, the roof is heated largely by the sun's radiant energy. Much of this heat gets to the attic side of the roof via conduction through the roofing materials. The warm roof material transfers its acquired heat energy onto the cooler attic surfaces, such as the air ducts and attic floor. A radiant barrier inhibits the flow of radiant heat from the underside of the roof to the attic's other surfaces.

The optimal orientation for a radiant barrier is perpendicular to the radiant energy striking it. Also, the bigger the differential in temperature between the two sides of the radiant barrier material, the greater the benefits a radiant barrier can provide.

Radiant barriers are more effective in warm areas than in cool climates, particularly when air ducts for cooling are positioned in the attic. In warm, sunny climates, radiant barriers can lower cooling expenses by 5 to 10 percent, according to some research. Reduced heat gain may permit a smaller air conditioning system. In cool climates, however, it is typically more economical to construct additional thermal insulation than a radiant barrier.

Types of Radiation Protection

Radiant barriers are composed of a highly reflective substance, typically aluminum foil, that is applied to one or both sides of a variety of substrate materials, including kraft paper, plastic films, cardboard, oriented strand board, and air infiltration barrier material. Some products are fiber-reinforced to improve their durability and manageability.

In reflective insulation systems, radiant barriers may be integrated with a variety of insulation materials. Radiant barriers can serve as the thermal insulation's face material in certain situations.

Installation

The efficiency of a radiant barrier depends on appropriate installation, so it is essential to hire a qualified installer. If you decide to perform the installation yourself, you should carefully review and adhere to the manufacturer's instructions and safety measures, as well as verify the local building and fire codes. Additionally, the reflective insulation trade organization provides installation advice.

It is easier to install radiant barriers in a new home, but they can also be installed in an existing home, particularly if the attic is exposed. In a new home, the radiant barrier is often draped foil-face down between the roof rafters to prevent dust gathering on the reflecting faces (double-faced radiant barriers are available). Typically, this is done right before the roof sheathing is installed, although it can also be completed from the attic by stapling the material to the bottom of the rafters.

When installing a foil-type barrier, it is essential to allow the material to "droop" between the attachment points to provide at least a 1.0-inch (2.5-centimeter) air gap between it and the bottom of the roof. Sheathing is also available in foil-faced plywood and oriented strand board.

Noting that reflective foil is an electrical conductor, employees and residents must avoid touching naked electrical wiring. It is strongly advised that radiant barriers NOT be put directly on top of the attic floor insulation, since the foil will be sensitive to dust gathering and may trap moisture in the fiber insulation if done in this manner.