White, Green and Cool
August 20, 2010
Maximizing the Value of Solar-Reflective Roof MembranesRoof systems 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 bituminous), field-applied coating or other type roof cover, such as sheet-metal, with a specified initial solar reflectivity and an “aged” reflectivity value a few years later. But the basic concept - reflecting the sun’s heat, absorbing and then emitting solar radiation - is well established. Cool roofs are definitely greener (to the extent that they are sustainable and minimize adverse environmental impact), and may contribute to interior comfort while reducing energy expenditures, but are not the vegetated or garden-surface variety signified by the term “green roof.” These roofs are also commonly designed with high insulation “R” values.
The cool roof idea has been around for several decades, but 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 a designer’s 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. Cool roofs, if properly maintained, can potentially 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. Some types of membranes with a slick reflective surface can be slippery when wet, so cautionary safety warnings and/or physical protective barriers may be necessary to safeguard maintenance personnel or others who might need to traffic across the roof. Generally, cool roofs are often more appropriate for warm, sunbelt-style climates with greater demands for cooling rather than heating, especially for buildings with minimal thermal roof insulation. Even where a cool roof is initially effective, targeted maintenance is still necessary for the roof to remain clean and reflective and thereby to stay cool and efficient throughout its lifecycle, providing true reductions in operating costs.
Roof MaintenanceCool roof maintenance is vitally important but is often overlooked. Dirt, soot, sediment and similar substances will still settle on a cool roof to some extent - making the roof darker and less efficient over time. Facility managers 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 can be lost. Maintenance should include mundane but necessary chores like regular unclogging of gutters and roof drains, avoiding water buildup which compromises the efficiency of the roof and contributes to deterioration. Additionally, for field-applied cool roof coatings, periodic re-coating should be planned and budgeted in order to maintain the continuity of the reflective surfacing. Finally, climate control devices and insulation should also be monitored and kept in good order because cool roofs are designed as a system that’s integrated with insulation and climate control for maximum energy savings. Insufficient maintenance is the biggest reason why some cool roofs don’t deliver the benefits their designer has promised.
The best way to ensure proper maintenance of cool roof systems is to consult a roof asset management specialist. Building Technology Associates (BTA), based in Detroit, is a good example of a firm with a wide variety of capabilities specifically focused on roof asset management. These capabilities include predictive modeling of where problems may occur, a database of various roof systems for comparison purposes, and “what-if” simulations to forecast the impact of various interventions (modify, repair, replace). A qualified roof asset management firm should also be able to advise owners on upgrades from conventional to cool roofs, perform feasibility studies, and prepare owners for the challenges of altering their existing design.
Are cool roofs a “cure-all” for environmental and energy-efficiency challenges? No. But combined with an appropriate sustainable roof system design, and an intelligent program of maintenance and roof asset management through its lifecycle, a cool roof can be greener and more cost-effective than other conventional alternative systems.
Dennis McNeil, RRC, CCS, RRO, is Senior Design Consultant in the Homewood, Ill., office of Detroit-based Building Technology Associates (BTA).
For more information, visit www.askbta.com.