Cool Roofing Explained
The surface of a traditional dark-colored roof can increase in temperature by up to 90-degrees on a hot sunny day. Some of this heat absorbs into the building, causing a huge increase in the cost of cooling the building. It can also lead to the “heat island effect” common in large, dense cities that have closely-spaced buildings not equipped with cool roofing.
Cool roofing is a name given to various types of roofing material designed to reflect sunlight and reduce absorption of heat that is radiating from the sun. It’s pretty simple to see how this works by comparing wearing a black t-shirt on a hot summer day and wearing a white t-shirt; you’ll sweat your butt off much more in the black shirt! The same is true for black and white colored roofs.
Many cool roofs are white in color, but recent advancements in roofing technology now allow for cool roofing in virtually any color. White reflects sunlight very effectively, but new colored cool roofing options contain sunlight-reflecting pigments to reflect the sun’s rays nearly as effective as white roofing.
Cool roofs may outlast traditional roofing in some climates, specifically hot climates. Heat and UV exposure can really take a toll on a roof. A black roof can reach temperatures of 150-degrees or more on a hot day, which can cause it to degrade relatively rapidly. Cool roofing, on the other hand, can help keep the roof’s surface as much as three times cooler, according to the U.S. Department of Energy. A cooler roof is more likely to last longer in extremely hot environments, such as the Southern United States.
The amount of sunlight reflected by the roof is its solar reflectance. The roofing industry measures a roof’s solar reflectance on a scale from 0 to 1. The percentage of sunrays deflected by the roof coincides with its solar reflectance; for example, a roof that deflects 40% of sunlight has a 0.4 score and one that reflects 75% of sunlight has a solar reflectance score of 0.75. The higher the number, the better the roofing is at staying cool.
A low-slope or flat roof is considered a cool roof if its solar reflectance is 0.55 or higher. A steep-sloped roof (most residential homes) is considered cool if the solar reflectance is 0.20 or higher.
Another way to measure a roof’s solar reflectance is the Solar Reflectance Index (SRI). The SRI is on a scale of 0 to 100 with higher numbers meaning a cooler roof. SRI factors in both the roof’s solar reflectance and thermal emittance (how efficient the roof cools itself). An SRI score of 64 or higher on low-slope roofing applications falls into the cool roofing category and 16 or higher in steep-sloped roofs qualify as being cool.
Cost of Cool Roofing vs. Traditional Roofing
Cool roofing is a premium roofing product, so expect the pricing to be slightly higher than comparable traditional roofing materials. However, the difference in cost between traditional roofing and cool roofing is decreasing as technology advances.
The roofing cost of cool products varies depending upon your location, complexity of the installation and the quality of the roofing product chosen. The EPA states most cool roofing products cost $0.05 to $0.10 per square foot more than conventional roofing products, on average. The U.S. Department of Energy says the difference in cost can range from zero to $1 per square foot. So the upfront price difference is significant, but generally not huge. The cost savings in the long term, however, can be quite substantial.
According to the Cool Roof Rating Council, cool roofing can reduce your cooling energy bills by 7% to 15% annually. On top of the energy savings, you can also receive federal and/or local tax credits for installing cool roofing products. Cool roofing falls under the Energy Star distinction, which can net you a tax rebate of 10% for the cost of materials up to a maximum of $500 (through 2013). Check your local tax incentives as well.
In addition to energy savings and tax rebates, cool roofing products often last longer than conventional roofing due to the fact the sunlight and heat don’t degrade the quality of the roofing nearly as quickly. The cost savings of cool roofing is much more pronounced in warmer climates compared to colder parts of the country.
Is Cool Roofing Right for You?
Maybe! According to the U.S. Department of Energy, the ideal locations for cool roofing in the U.S. fall within Zones 1, 2 and 3 on the map below. In any of the other areas of the country, cool roofing may actually increase energy costs in the home due to less of a beneficial heat gain effect during the winter months.
Talk to a local roofing contractor to determine if cool roofing is an option worth looking into.