Solar Reflectance Index Metal Roofing

Link between energy savings and emissivity.

Solar reflectance index metal roofing.

For an asphalt roofing shingle to be classified as a cool under the energy codes it needs to have a cool roof rating council crrc rating for thermal emittance and solar reflectance. Solar reflectivity or reflectance is the ability of a material to reflect solar energy from its surface back into the atmosphere. Leed 2 2 sustainable sites credit 7 2 states that to receive one point building owners should use a roof with a solar reflective index sri of 78 over at least 75 percent of the roof s surface for roofs with slopes less than 2 12. Recycled content of berridge metal.

Sri is a unit developed by scientists at lawrence berkeley national laboratory. The attic under the roof. A cool metal roof with high solar reflectance and high thermal emittance would have a lower surface temperature as compared to a roof with low reflectance and low emittance. After 3 years the solar reflectance must be 0 15.

The solar reflectance index sri is a measure of the constructed surface s ability to reflect solar heat as shown by a small temperature rise. Solar reflective shingles are designed specifically to reduce the absorption of the suns infrared radiation by reflecting ir rays off the surface of the roof thus not allowing the heat to be transferred to the interior of the structure i e. Solar reflectance index sri. After 3 years the solar reflectance must be 0 50.

Incorporates both solar reflectance and thermal emissivity in a single value. Solar reflectivity r solar reflectance index sri by color. It also must meet the specific solar reflectance thermal emittance and or solar reflectance index values defined by the specific energy code. Only those roof products that meet the specifications.

Solar reflectance is the most important characteristic of a roof product in terms of yielding the highest energy savings during warmer months. A value of 0 indicates that the material absorbs all solar energy and a value of 1 0 indicates total reflectance. In the case of a cool metal roof a lower surface temperature translates into less heat gain into the attic space or living space below the roof. Sri measures the roof s ability to reject solar heat defined such that a standard black reflectance 0 05 emittance 0 90 is 0 and a standard white reflectance 0 80 emittance 0 90 is 100.

It is defined so that a standard black surface reflectance 0 05 emittance 0 90 is 0 and a standard white surface reflectance 0 80 emittance 0 90 is 100. One example is a metal wrench left in the sun which is hot to the touch because it has a low emissivity value.