White, Green, and Cool: Maximizing The Value Of Solar-Reflective Roof Membranes

Roofs are an important element in green, sustainable, architectural solutions. One of the more interesting concepts in energy efficiency is the “cool roof,” also sometimes known as a “white” or even “green” roof. The terms are not really interchangeable -- the cool roof concept is specifically defined by the Cool Roof Rating Council (CRRC) as a roof membrane (single-ply, built-up, or modified bitumen), field-applied coating or other type of roof cover (such as sheet-metal), with both a specified initial solar reflectivity and an “aged” reflectivity value. The basic concept -- reflecting the sun’s heat, absorbing and then emitting solar radiation -- is well established.

Cool roofs are definitely green (to the extent that they are sustainable and minimize adverse environmental impact) and may contribute to interior comfort while reducing energy expenditures, but they are not the garden-surface variety of the term “green roof.” Green roofs are also commonly designed with high insulation R-values.

The cool roof idea has been around for several decades, but it has gained importance with increasing environmental concerns. Building codes feature stricter standards regarding R-values and roof materials (e.g., thermal resistance value must be 20 or greater), while environmental issues add a social awareness element -- cool roofs can enhance your reputation. Materials have changed, too; a wide variety of roof membrane and coating materials are available to designers, including light (but not necessarily pure white) colors.

Caveats for Cool
Cool roofs, if properly maintained, can also reduce energy costs, thus beneficially impacting an owner’s bottom line. There are some caveats regarding cool roofs, however. 

Roof surfaces should be positively sloped to minimize the accumulation of dirt in low spots and to likewise aid in “self-washing” during normal rain.  Cool roofs are particularly appropriate for warm, sunbelt-style climates like ours with greater demands for cooling rather than heating.

Targeted Maintenance
Even when a cool roof is initially effective, targeted maintenance, which is often overlooked, is still necessary for the roof to remain clean and reflective so that it can stay cool and efficient throughout its lifecycle. Dirt, soot, sediment and similar substances will still settle on a cool roof  making the roof darker and less efficient over time. We must invest some time, effort and money in monitoring the roof’s condition and performing cleaning or repairs as necessary. Otherwise, energy-efficiency declines and cool roof benefits are largely lost.