Roof Coating

A cool roof is designed to reflect sunlight (solar energy) and effectively release any heat it absorbs. This characteristic helps the roof stay cooler, thereby reducing the amount of heat transferred into the building below. For buildings without air conditioning, a cool roof contributes to maintaining a lower and more consistent indoor temperature. In buildings with air conditioning, the cooling units do not have to work as hard, which can lead to energy savings.

To illustrate, consider the difference between wearing a white T-shirt and a black T-shirt on a hot day. The white T-shirt reflects more sunlight and absorbs less heat, keeping you cooler. Similarly, cool roofs function like white T-shirts, helping to keep the internal temperature of the building lower.

Cool roofs do not have to be white. Various "cool color" products utilize darker pigments that are highly reflective in the near-infrared (non-visible) part of the solar spectrum.

The two main characteristics that define a roof's "coolness" are solar reflectance and thermal emittance. Both properties are assessed on a scale from 0 to 1, where 1 indicates 100% reflectivity or emissivity.

This illustration describes the flow of radiant energy as heat between the sun, roof surface, building interior, and surroundings. The higher the solar reflectance, the more solar energy is reflected away from the roof surface. Some of the solar energy is absorbed by the roof as heat. The higher the thermal emittance, the more of this absorbed heat is radiated away from the roof surface. Source: Cool Roof Rating Council

Property owners with a roof coating may incur slightly higher heating costs in winter; however, this drawback is minimal compared to the cooling energy savings realized in summer.

Why?

In winter, the sun is positioned much lower in the sky and its intensity is reduced. Additionally, sunshine that streams through windows can contribute to passive solar heating. Winter days are shorter, resulting in fewer hours of sunlight, and there tends to be a higher frequency of cloudy days. A cool roof does not lose more heat compared to other roofing materials at night or on cloudy days. Its primary function is to limit the amount of heat entering the building during hot summer days. In some areas, roofs can be covered in snow for extended periods, making the color of the roof below less significant.