Whether on a building or a home, the roof plays a major role in the absorption of heat from sunlight—this is known as solar radiation. Heat can either be reflected into the atmosphere, or absorbed through conduction into the building. When sunlight is absorbed it will heat the roof’s surface, and the more solar radiation absorbed, the greater the need to release the heat.
Emissivity is the measurement of the roof’s ability to shed absorbed heat.
The overall roof’s design such as type, color, and elevation will determine how the heat is reflected, and the absorbed heat is released. The goal of cool coating technology is to be able to reflect solar radiation and shed what heat is absorbed away from the surface of a building or home.
Coatings colored with conventional pigments absorb infrared radiation. By replacing the conventional pigments with cool pigments there is less infrared radiation absorption. Cool coatings lower roof surface temperatures, reduce the need for cooling energy in conditioned buildings, and make unconditioned buildings more comfortable.
Cool pigments work by absorbing and reflecting different parts of the sun’s wavelength spectrum based on their chemistry. They selectively absorb visible light, and what light it reflects appears to the human eye as color. Nearly 40% of the sun’s energy occurs in the visible light range (400 to 700 nm), more than 50% of the sun’s energy is in the non-visible infrared region (700-2500nm). It’s the infrared (IR) that is largely responsible for heat build-up.
The two types of pigments used in coatings are organic and inorganic. Organic pigments offer very vivid and bright colors but are not as opaque as inorganic pigments. Inorganic pigments known as Complex Inorganic Color Pigments (CICP) are used on metal roofing. The pigments within this group display high IR-reflectivity for a given visible color.