Radiant barriers are installed in homes — usually in attics — mainly to reduce summer heat gain and lower cooling costs. The barriers comprise a highly reflective material that reflects radiant heat rather than absorbing it. They don’t, however, lower heat conduction like thermal insulation materials.

How Radiant Barrier Works

Radiant Barrier Insulation Installation

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Heat travels from a hot zone to a cool area through a combination of conduction, convection, and radiation. Heat flows by conduction from a warmer location within a material or assembly to a colder area, like how 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 instance — is heated, becomes less dense, and rises. As the liquid or gas cools, it becomes thicker and falls. Radiant heat travels in a straight line away from any area and heats anything substantial that absorbs its energy.

Many insulations materials work by slowing conductive heat flow and convective heat flow to a lesser extent. Radiant barriers and reflective insulation systems work by lowering radiant heat gain. The reflective surface faces an air space to be effective. Dust accumulation on the reflective surface will reduce its reflective ability. The radiant barrier should be installed in a manner that minimizes the accumulation of dust on the reflective surface.

When the sun heats a roof, it’s mainly the sun’s radiant energy that makes it hot. More 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 and the air ducts and the attic floor. A radiant barrier decreases the radiant heat transfer from the underside of the roof to the other surfaces in the attic.

A radiant barrier works finest when it is perpendicular to the radiant energy striking it. The greater the temperature difference between the sides of the radiant barrier material, the higher the benefits a radiant barrier can offer.

Radiant barriers are most effective in hot climates than in cool climates, especially when cooling air ducts are located in the attic. Some researches indicate that radiant barriers can reduce cooling costs by 5% to 10% when used in a warm, sunny climate. The reduced heat gain can even allow for a smaller air conditioning system. Nevertheless, it’s usually more cost-effective to install more thermal insulation than to add a radiant barrier in cool climates.

Types of Radiant Barrier Attic Insulation

Radiant barriers comprise a highly reflective material, usually aluminum foil. It is applied to one or both sides of a number of substrate materials such as kraft paper, plastic films, cardboard, oriented strand board, and air infiltration barrier material. Some products are fiber-reinforced to surge durability and ease of handling.

Radiant barriers can be combined with many kinds of insulation materials in reflective insulation systems. Here, radiant barriers can act as the thermal insulation’s facing material.

Radiant Barrier Installation

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A radiant barrier’s effectiveness depends on proper installation, so it’s best to use an accredited installer. If you opt to do the installation yourself, carefully study and follow the manufacturer’s instructions and safety precautions and check your local building and fire codes. The reflective insulation trade association also provides installation tips.

It’s easier to integrate 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 home, 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 usually done just before the roof sheathing goes on, but can be done afterward from inside the attic by stapling the material to the bottom of the rafters.

When installing a foil-type barrier, it’s vital 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. Foil-faced plywood or oriented strand board sheathing is also offered.

Note that reflective foil will conduct electricity, so employees and homeowners must avoid making contact with bare electrical wiring. If installed on top of the attic floor insulation, the foil will be susceptible to dust accumulation. It may trap moisture in fiber insulation, so it is strongly advised that you NOT apply radiant barriers directly on top of the attic floor insulation.

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