Keeping it cool

A cool roof case study investigates white roofs' energy efficiency

After 18 years of exposure to extreme desert heat, the roof system on the Nationwide® Scottsdale Insurance Co. headquarters building in Scottsdale, Ariz., began to deteriorate. The maintenance staff had been chasing leaks for nearly five years when Nationwide Scottsdale Insurance decided to hire Alan Stevens Associates Inc., Cedar Rapids, Iowa, to solve the problem and replace the roof system.

The building's original roof system was a ballasted EPDM membrane over 4 inches of polyisocyanurate insulation on a concrete roof deck blanketed with a 2-inch-thick layer of river rock. The roof system was becoming a liability with regard to structural integrity (from water damage), maintenance costs and energy consumption.

The new roof system was installed by Starkweather Roofing Inc., Phoenix, in December 2008 and consists of 3 inches of polyisocyanurate board insulation set in roof adhesive over the concrete roof deck and a self-adhering base sheet and self-adhering white laminated polymer-modified bitumen roof membrane over the top. The membrane's surface is a reflective white film laminate with a solar reflectance index (SRI) value of 84.

In July 2009, the Arizona Cool Roof Council asked Starkweather Roofing to conduct a case study to determine whether white roofs truly are cooler and more energy-efficient than nonwhite roofs. The Nationwide Scottsdale Insurance building's roof was an ideal choice for the in-depth study.