Cool roofs refer to roofs that are cool in both senses of the word. Lighter in color than traditional black asphalt or dark wood shingles, cool roofs save energy by reflecting light and heat away rather than absorbing both. This is known as the albedo effect, and study after study in the last few years has documented significant energy savings from simply lightening the color of a roof.
- The problem with dark roofs: The temperature outside may be 95 degrees, which is plenty hot, but your dark roof is conducting a much higher temperature down at you and your family, making the rooms below hotter and making the air conditioner work harder, Barbara Collins points out in her answer to the Ask A Pro question "NYC has a 'cool roof' program. Is there a white paint or coating to make my roof cooler?" In New York City, she notes, a dark-colored asphalt roof can reach 150 to 175 degrees on a hot summer day. This not only increases the energy needs of your home, it also contributes to the heat island effect in urban areas.
- The benefits of cool roofs: A cool roof, on the other hand, can be 50 to 60 degrees cooler than a conventional dark-colored roof, reducing the cooling load on your home, saving energy, and reducing utility costs. By decreasing the solar gain and heat retention of your home, a white roof also increases its comfort and reduces the heat island effect that your home’s dark roof contributes to.
- How to cool your roof: The easiest route is to slap a cool roof coating onto an existing roof. Check out these recommendations from Dave Edwards, PhD, of EarthBound Homes, for coating options. If you’re already re-roofing, or building a new residence, consider replacing shingles or asphalt with lighter-colored versions of themselves. If you’ve got a flat-top roof, Edwards suggests DuraLast’s sheets of fiber-reinforced white PVC membranes, in his Q&A "I'm reroofing a typical sloped roof -- what materials should I be considering?" A quick search of the Cool Roof Rating Council’s Rated Products Directory, will provide you with performance data about various roofing products. Products are rated for their reflectiveness on a 0 to 1 scale; the higher the number, the more reflective the product is, and the cooler your roof will be.