Solar Reflectance Of Roofing Materials

Link between energy savings and emissivity.

Solar reflectance of roofing materials.

The sr value is a number from 0 to 1 0. Solar reflectance and thermal emittance are the two key material surface properties that determine a roof s temperature and they each range on a scale from 0 to 1. The solar reflectance measurement ranges between 0 0 and 1 0 with 1 0 representing 100 reflectance with no absorption. Unpainted metals are typically good solar reflectors but poor thermal emitters so they rarely satisfy low slope cool roof requirements.

Reflective surfaces can deliver high solar reflectance the ability to reflect the visible infrared and ultraviolet wavelengths of the sun reducing heat transfer to the surface and high thermal emittance the ability to radiate absorbed or non reflected solar energy. Reflective surfaces are a form of geoengineering. With the exception of a metallic surface most roofing materials can have emittance values above 0 85 85. Energy star requires an initial sr value of 0 25 or higher for steep slope 2 12 roofs and 0 15 or greater after three years.

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. Scientists use a number between 0 and 1 or 0 and 100 to express emittance. Metal roofs are available with natural metallic finishes oven baked paint finishes or granular coated surfaces. Roofing shingles and materials plus factory certified roofers including ratings from real homeowners from north america s largest roofing manufacturer.

Using solar reflective shingles and solar reflective roofing products that reflect ultraviolet and primarily infrared radiation will reduce damage caused by u v and heat degradation. The larger these two values are the cooler the roof will remain in the sun. Asphalt shingles with higher solar reflectance values can achieve energy star certification. A value of 0 indicates that the material absorbs all solar energy and a value of 1 0 indicates total reflectance.

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. How they can be made cool. Heat island effect roof.