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What is Thermal Emittance?

More roofing definitions

Thermal emittance refers to the ability of a material to radiate the heat that it absorbs. For example, a metal roof which gets so hot in the sun that it burns to the touch has a low thermal emittance. Heat is absorbed but not released. A surface with a high thermal emittance will both absorb heat and radiate back into the environment.

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. Sometimes, the rating is expressed in a percentage. A lower number means a better performing product.

Thermal emittance is a helpful measurement that can be used in calculating ways to reduce heating and cooling energy costs in buildings. Thermal measurements can only be taken in the infrared wavelength using special instruments that measure heat waves.