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Going Green – Installing A Radiant Barrier

Radiant barriers usually are a thin sheet of reflective material, typically aluminum, which is applied to one or both sides of materials in your home. Using these materials can greatly reduce your summer heat gain and winter heat loss. The materials used for the barrier can include: plastic films, cardboard, plywood, and air barrier material. Fiber reinforcement can increase the durability of the barrier.

The simplest way to install a radiant barrier in a residential attic is to lay the material directly on top of the attic insulation with the reflective side up. Another option is to attach it near the roof. You could attach the material to the bottom of the trusses, or you could attach it to the underside of the roof deck.

The way they work is by reducing the heat transfer across the air space between the attic roof and attic floor. Every material will give off energy by thermal radiation based on its temperature. In order to work properly, the materials used in a radiant barrier must have a high reflectivity (90% or more), as well as a low emissivity (10% or less). The barrier must also face an open air space.

When it is sunny, the roof absorbs the heat, which causes the underside of the roof to radiate heat toward the attic floor. With a radiant barrier placed on top of the attic floor, most of the heat from the hot roof is reflected back toward the roof. This results in the top of the insulation remaining cooler, which causes less heat to pass through the insulation and into the rooms below the ceiling.

In Winter months, the radiant barrier will also reduce the heat lost through the insulation as it rises through the home. However, in colder climates, you also will not receive the benefit of the sun heating the roof. Studies are still going on as to whether a radiant barrier helps during the Winter. The benefits may be a wash in the Winter.

Conventional insulation works by trapping the heated air within its fibers, which reduces heat transfer by air movement. The fibers also partially block radiant heat transfer.

All radiant barriers will have at least one reflective surface, usually a coating of aluminum. Some will be reflective on both sides. Keep in mind that if a one-sided barrier is used, the reflective side must face the open space, or it will lose more or all of its usefulness.

Another thing to keep in mind is that a radiant barrier in an attic floor installation must allow water vapor to pass through it. During the winter, water vapor from the living areas may condense and freeze on the underside of an attic floor radiant barrier. A layer of condensed water can also build up. Some radiant barrier materials allow water vapor to pass through perforations, while other will allow water vapor to pass without holes. Roof applications do not need to pass water vapor.

A.C. T. Services would be honored to have the opportunity to install a radiant barrier to reduce your heating and cooling costs, and to improve your energy efficiency. We can put our 31 years of experience to work in making your home more “green.” We will make the energy project save you money, as well as take a small step toward saving the planet for the next generation. Most of all, you are the most important member of our remodeling team.

Gary Harris



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