Just about any kind of roof can be replaced with a cool roof, and some can be converted to cool roofs with the addition of special coatings or surface materials. In some states and municipalities, cool roofs are already required for all new commercial construction. Cool roof requirements are based on the roof's slope, with more stringent requirements for low-sloped roofs, which rise less than 2 feet (0.6 meters )in height for every 12 horizontal feet ( 3.7 meters), than for steep-sloped roofs, which rise more than 2 feet (0.6 meters )in height every 12 horizontal feet ( 3.7 meters) [source: Department of Energy].
To determine which roofing materials are best for your home or building, first determine the slope of your roof, then select the cool roof product that best suits your slope, budget, and architectural style.
One of the most common cool roof options for a flat or low-sloped roof is a modified bitumen roof. Modified bitumen roofing is a membrane made up of sheets of plasticized or rubberized asphalt held together with rolled reinforcing fabric and fastened to the roof deck with hot asphalt or cool adhesive. Traditional modified bitumen roofs are black or gray, with a low solar reflectance, meaning that they absorb, rather than reflect, most of the sun's light. But simply applying a white coating over the surface of the material at the factory can raise the solar reflectance to acceptable cool roof standards. The price of a cool modified bitumen roof is about the same as the price of a "hot" modified bitumen roof: about $1.50 to $1.95 per square foot [source: Pacific Gas and Electric].