A new roof and attic system being developed by the Department of Energy's Oak Ridge National Laboratory (ORNL) could reduce homeowners' utility bills by eight percent or more. Active thermal mass components, reflective pigments and coatings, subventing, radiant barriers, and other techniques are all being tested by ORNL's Building Envelopes group.

The prototype roof and attic system reduces attic temperatures by about 22 degrees Fahrenheit during a typical summer afternoon, and decreases the amount of heat that gets transferred through the attic floor to the living space. At the heart of the system is a proprietary inorganic phase change material sandwiched between two reflective surfaces made of aluminum foil. This material is installed as a dynamic thermal barrier between the roof and attic area, creating separate air channels between roof rafters.

The configuration is compatible with traditional wood and steel framing technologies. ORNL researchers are working with leading manufacturers of phase change material to develop non-flammable organic material, eliminating the problem of fire.

In tests at ORNL, phase change materials performed like conventional materials by absorbing heat as the temperature increased. As the material melted, it continued to absorb heat without a significant increase in temperature. As night fell and the ambient temperature around the liquid phase change material decreased, it solidified again and released the stored heat to the night sky.

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