What is Cool Roofing?

Any roof material with a reflective coating and high rate of emittance may be called a ‘cool roof’. For example, foam Roofing is defined as a "cool roofing" material, mostly because rubberized coatings must be used with SPF applications, and these coatings are generally reflective. On rare occasions non-standard coatings, which might not meet energy star standards for reflectively and color (for example, based on customer requests).

Cool Roof Definition

Any roofing system with high solar reflectivity, including visible, infrared, and ultraviolet wavelengths of the sun, and in turn reduce heat transfer to the structure is a cool roof. To be defined as a ‘cool roof’ the roof system must also have a high rate of thermal emittance, or in other words, the capacity to release most of the energy or light that is not directly reflected.

Below: Most polyurethane foam roofing systems like the one below use a reflective or 'cool roof' coating like this roof below. Cool roof coating greatly reduces the surface temperature on roof systems, preserving the life of the roof and reducing cooling bills by 20% or more.

Solar Reflectance Index (SRI)

The solar reflectance index (SRI) is the newest method of evaluating the reflectivity of a surface with black and white surfaces appearing at the opposite ends of the spectrum. SRI considers both reflectance and emittance in a single value, with the standard of black at 0 (.05 reflectance/ .90 emittance) vs white at 100 (.80 reflectance/ .90 emittance).

Although a cool roof complements insulation making both synergistically more effective, sometimes cool roof coatings are used as an alternative to attic insulation. This is only effective with a highly reflective roof surface that reflects both visible and non visible light spectrums as well as emits a high rate of absorbed energy back into the atmosphere.

Below: The image below displays visually how increased solar reflectance reduces the roof temperature. These cooler roof temperatures may help reduce cooling bills by 20% or more. It's amazing how simply changing the color of the roof material can chance the interior living environment.

Cool Roof Benefits

Worldwide, most roofs are dark colored and non reflective. In fact, in the united states, less than 10% of all roofs can be defined as ‘cool roofs’. Cool roofs reduce roof surface temperatures, improve indoor comfort, cut heating and cooling bills and extend the life of the roof.

Non-reflective asphalt roof surface often reach temperatures of 150-190 degrees Fahrenheit or more on a 90 degree day. On a similar day, a ‘cool roof’ will only reach a temperature around 110 degrees (or 10-25 degrees F above the current ambient temperature). By reflecting UV, infrared, and visible light, and by keeping the roof surface cooler, reflective cool roof coatings extend roof life. In contrast, a non cool roof surface ‘cooks’ the roof materials at a high temperature, prematurely aging the roof (and results in a shorter roof life).

By extending the roof life, landfill waste is diverted, resulting in less waste, making the roof ‘greener’ and more environmentally friendly. Air pollution is also reduced due to mitigation of the urban heat island effect. The urban heat island effect is the net result of dark non reflective roof surfaces, black asphalt streets, vehicle exhaust, and air trapping due to small spaces between large buildings, resulting in temperature increases of 10 degrees or more in the immediate vicinity of a city. This interrupts local weather patterns and increases fossil fuel usage due to increased air conditioning demands. Dark roof surfaces are a primary cause of urban heat islands, and in turn, cool roof coatings are a primary solution.

The cooler roof temperatures also significantly reduce utility costs for building occupants. Homes stay more temperate with cool roof coatings, increasing indoor comfort. The life of air conditioning units is also extended with the decreased usage. These types of benefits can be expected, even in northern climates. In fact, during warm weather, a cool roof alone can reduce electric power usage by 10% or more. Scientific studies have shown that insulation performance is greatly reduced at extreme temperatures. By keeping the roof temperature cooler, the existing insulation stays cooler and becomes more effective as well. For all these reasons, cool roofs provide both immediate and long term costs in building energy costs.

Cool Roofing Should be Used Worldwide

I usually think of cool roofing as something you put on a roof (like a foam roof) that is already insulated. It does make sense that a cool roof even without insulation makes a substantial impact. I don't see why the government just makes it a law for buildings to have cool roof coatings. I know California passed something like this (title 24) in 2005. Really, a cool roof coating is nothing special, so much as it is just choosing a light color for a building. There's no reason why it should not be a construction standard throughout the USA, and even throughout the world. Everyone talks about cutting down on fossil fuel usage.. here's something that can be done worldwide without really creating any additional cost burden on any economy.

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I have heard a lot of companies talk about 'cool roof coatings' but i never quite understood what the big deal was. Thanks for the post, this help me make better sense of things.