High Thermal Emittance Roof

The term solar reflectance is a measure of the amount of that solar energy that is immediately reflected from the surface.

High thermal emittance roof.

Ideally you ll want a roof that has equal reflectance and emittance because they complement one another. Aged solar reflectance tested in accordance with astm c 1549 astm e 903 or. One example is a metal wrench left in the sun which is hot to the touch because it has a low emissivity value. Painting a metal roof can increase its solar reflectance and thermal emittance allowing it to achieve cool roof status.

Mindful that reflectance and albedo can be different a combination of high albedo and high emittance resists solar heat gain most effectively. Sometimes the rating is expressed in a percentage. In general a cool roof is one that has relatively high solar reflectance and high thermal emittance. With the exception of a metallic surface most roofing materials can have emittance values above 0 85 85.

Materials lacking 3 year aged tested values for either solar reflectance or thermal emittance shall be assigned both a 3 year aged solar reflectance in accordance with section c402 3 1 and a 3 year aged thermal emittance of 0 90. Just like reflectance the emittance of the roof is measured on a scale of 0 to 1 with 1 being the highest. How they can be made cool. This physics related article is a stub.

Scientists use a number between 0 and 1 or 0 and 100 to express emittance. You can help wikipedia by expanding it. However emittance also matters because the higher the emittance the more readily the roof surface will radiate long wave ir heat to the sky. They can also reduce the urban heat island effect.

The thermal emittance of roofing surfaces is rated by the american society for testing and materials better known as astm. Like solar reflectivity materials are rated on a scale between zero and one. During the daylight hours a roof is constantly subjected to solar energy striking its surface. The thermal emittance of a roof or wall component is mainly affected by the characteristics of the layer that is exposed to the solar radiation.

In common construction applications the thermal emittance of a surface is usually higher than 0 8 0 85 except for those layers that are based on metallic components for example aluminum shingles. Alternatively you can apply cool reflective coatings. A surface with a high thermal emittance will both absorb heat and radiate back into the environment. Link between energy savings and emissivity.

The use of area weighted averages to comply with these requirements shall be permitted. A roofing surface with high solar reflectance and high thermal emittance will reflect solar heat and release absorbed heat readily.