Cool Roofs

Posted: July 18, 2012 - 1:59pm | Y-12 Report | Volume 9, Issue 1 | 2012

Hot, sunny days call for light-colored clothing to reflect the heat. As it turns out, the same principle works for roofs.

Consider the results from a Lawrence Berkeley National Laboratory study in Austin, Texas, which measured a dark roof to average a whopping 43 degrees hotter than a light roof. The hotter the roof, the hotter the building becomes, and the more air-conditioning is needed — 11 percent, in that particular study. That in turn puts more carbon dioxide into the atmosphere. Higher atmospheric temperatures also affect atmospheric chemistry, causing higher ozone levels and more smog.

Turning down the heat can be both inexpensive and simple, however: replace the heat-absorbing dark roofs with “cool roofs” that are light-colored instead of dark. Cool roofs reduce building cooling costs, offset carbon emissions and eliminate the use of coal tar pitch or asphalt, which are petroleum-based products. According to the Environmental and Energy Study Institute, “whitening flat roofs is a low-cost solution which, if implemented in certain cities across the globe, has been estimated to have the potential to offset the carbon emissions of 300 million automobiles.”

Y‑12 began installing cool roofs in 2008, which was well before Secretary of Energy Steven Chu's July 2010 mandate that all Department of Energy facilities use cool roofs, where feasible, when constructing new buildings or replacing older roofs. Fifteen percent of Y‑12's roofs are now cool, and Mike Richesin, program manager of the Facilities and Infrastructure Recapitalization Program, said, “Ultimately we expect that 90 percent of our roofs will be cool roofs. There will be a few for which the cool roof technology is inappropriate. All of our new buildings, of course, are or will be cool roofs.”

In the past decade, more than 20 acres of old roofing at Y‑12 have been replaced with new roofing. Of that number, six acres, or 258,000 square feet, are white roofs. Energy savings are not as dramatic as those in the Austin study because Oak Ridge, Tenn., has a cooler climate than Austin, Texas. Cool roofs also deflect some of the heat gain that's desirable in winter, but overall, they still save energy. Charlie Sexton of Facilities, Infrastructure and Services quantified the savings using the DOE Roof Savings Calculator and found a few hundred dollars a year in savings for a 30,000-square-foot roof. “The calculator shows a significant savings with increased insulation,” he said. “When we re-roof buildings at Y‑12, we also increase the insulation to R-30 between the roof deck and the roofing membrane. Over the 20- to 30-year life of the roof, the savings add up. It is definitely worth having a white roof to reflect the heat.”

Y‑12 is replacing the site's older roofs as part of the National Nuclear Security Administration's Roof Asset Management Program, known as RAMP. “It manages priorities for roof replacement based on comprehensive roof assessments at each NNSA site, which are entered into a current database,” said Richesin. “Three things determine when roofs can be replaced: the comprehensive assessments, the deferred maintenance backlog and a database of leaks.” As Y‑12 moves toward its expected goal of 90 percent cool roofs, it will save energy and, better still, the environment.