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Radiant Barriers

Technology Snapshot & Benefits:
The roof is a large source of heat in many homes. Rays from the sun enter through the roof, and while heat is absorbed by the attic, some heat diffuses down through the attic floor and throughout the house. In the winter, heat is also easily lost through the roof. A well-insulated roof can have a big impact on a home's cooling costs, and some impact on heating costs. Radiant barriers prove to be some of the most effective insulation that can be installed in a roof.

Most attic roofs already have some form of insulation. Radiant barriers are an additional layer of insulation made from a thin sheet of aluminum or an aluminum-coated substrate, such as cardboard, plastic film, or plywood sheathing. In warm weather, they work by reflecting heat absorbed through the roof back into the roof, instead of allowing heat to permeate through to the attic and/or the rest of the home.

During the winter, radiant barriers can reduce heat lost through the roof, but can also reduce heat absorbed through the roof. Research on the net benefits of radiant barriers in winter is ongoing. However, radiant barriers have been shown to reduce energy demands in many residential, commercial, and industrial buildings.

Estimated Cost Savings:
Studies have shown that radiant barriers may cause a 10 to 30 percent reduction in peak demands for energy. This number can be increased by adding additional layers of insulation with the radiant barrier. The effectiveness of the barrier depends on the emissivity and reflectance of the material used. Emissivity is a number from 0 to 1, depending on the amount of radiation emitted through the barrier. Reflectance is also a number between 0 and 1, but is usually represented by a percentage. The higher the reflectance and lower the emissivity, the more effective the material. Aluminum is almost always used for radiant barriers because of its high reflectivity, although other materials are sometimes used. Materials used for radiant barriers should have reflectance of at least .9 (90 percent) to be most effective. Some radiant barriers are now being assigned R-values. R-values are based on the amount of time it takes a material to absorb 100 percent of its potential and start transferring heat out the other side. In the case of radiant barriers, the higher the R-value, the better.

Installation of radiant barriers is usually inexpensive. Costs range from $.02 to $.31 per square foot, depending on where the barrier is installed, the manufacturer of the barrier, and whether or not the barrier is installed by the homeowner or a professional. However, the long-term benefits, especially in warmer areas where cooling costs constitute a considerable monthly expensive, far outweigh the initial cost of the barriers.

Issues:
It is very important that radiant barriers be installed in well-ventilated homes, no matter where or how they are installed. Without proper ventilation, water vapor can build up between the barrier and the roof or wall and cause serious water damage. It is important to check with an expert to make sure your home is properly ventilated before installing radiant barriers.

Regional Issues:
Radiant barriers are most effective in areas where cooling and/or heating costs constitute a significant monthly expense. It is not yet known whether the winter cost savings from reducing heat loss through the roof outweighs the reflected solar heat usually absorbed through the roof. Home or business owners looking to reduce heating costs in regions where the weather is usually cold should research other ways to reduce heating costs until solid conclusions on the net benefits of radiant barriers in the winter can be drawn.

Installation:
Radiant barriers can be installed in a variety of ways: by laying the barrier on top of the existing insulation, radiant side up; by attaching directly to the underside of the roof deck; by draping over the tops of the rafters before putting on the roof; or by placing them in the walls, with the reflective side facing the ventilated space. The first methods are easier to install in homes that have already been built, while the latter two methods are more commonly used during initial construction. As mentioned above, it is extremely important to ensure that a home or business is properly ventilated before installing radiant barriers.

Radiant barriers should be installed with the reflective side up or out (if installed in the wall), with some dead space between the barrier and other insulation. It's best not to staple multiple radiant sheets together, but to overlay them instead.

Radiant barriers can be installed by a professional contractor or a homeowner; however, it is important to get expert advice before installing your own barrier.

Videos On This Topic:

How Attic Insulation and Radiant Barrier Work Together in Cold Weather (4:40) - Attic Foil - By placing a radiant barrier over insulation in your attic, you can help protect your home from unnecessary heat loss and reduce your heating and cooling bills significantly.  In this video, find out more about how radiant barriers can help make your insulation more efficient and how the two pieces work together to increase your home�s energy efficiency.

More Information On This Topic:

"Radiant Barrier Attic Fact Sheet"
U.S. Department of Energy

"Installing Radiant Barrier Insulation"
Do It Yourself

"Radiant Barriers"
U.S. Department of Energy - Office of Energy Efficiency and Renewable Energy

"Radiant Barriers Energy Fact Sheet: Principles, Savings, Pros and Cons, Techniques"
Southface Energy Institute

 


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