New Jersey’s Atlantic City Convention Center is the largest single roof-mounted, grid-connected solar system in the United States. At almost 500,000 square feet, the project is a huge investment for the city, which wasn’t about to gamble on its new roof. Facility managers wisely chose to enhance their energy saving investment with a durable and highly reflective TPO (thermoplastic polyolefin) roof membrane.

Reflective roofs like TPO can enhance the energy efficiency of solar roofing systems by up to 20 percent by reducing rooftop temperatures. In addition, GAF’s Freedom™ TPO is self-adhered and does not require the use of solvent-based adhesives or hot asphalt, making the Atlantic City project that much “greener.”

The convention center roof is also unusual in that most solar installations require that the existing roof be torn off. However, that wasn’t an option in Atlantic City. The dynamics of the convention center roof and the extra cost of a tear-off would have put the project way over budget.

The existing roof, a 12-year-old granular surfaced modified bitumen also manufactured by GAF, was performing well and subject to yearly evaluation and maintenance. However, at some point during the 20-year life of the solar system, this roof would have to go.

“We explained that the convention center would be responsible for a very difficult tear-off sometime in the future,” said Herb VanGent, eastern area manager of field operations for GAF. “To its credit, the facilities team chose to recover with the reflective TPO membrane.”

In addition, there were concerns about the effects of a tear-off on the building’s lightweight concrete deck. “If we tore off the modified bitumen, we would have disturbed or damaged the underlying deck,” said Frank Moore, AIA and president of roof consulting firm ARMM Associates Inc., Cherry Hill, N.J. “Fortunately, we found that the building was easily able to handle the additional weight of a second roof system and the solar panels.”

Thomas Company Inc., a full-service roofing and sheet metal contractor based in Atlantic City, was chosen to install the new membrane. Roofing crews first power washed the surface of the modified bitumen roof and secured a 3/8-inch gypsum cover board over the existing membrane with Olybond500 insulation adhesive.

OlyBond500 is a dual-component, low-rise polyurethane foam adhesive manufactured by OMG Roofing Products of Agawam, Mass. It is designed to attach insulation to roof decks without noxious odors that may disturb building occupants. The foam is also low in VOC content and meets Factory Mutual (FM) I-90 wind uplift standards required by the State of New Jersey for the convention center project. In addition, GAF-supplied Drill-Tec Impact Locking Nails used to enhance wind resistance around the perimeter of the roof.

“Thomas Company did a great job installing the Freedom TPO membrane,” said Moore. “There wasn’t even one blister or lump in almost 500,000 square feet of new roofing, and the GAF membrane went down very smoothly. We also found that the TPO membrane and cover board were adequate to handle the additional roof traffic and maintenance required for the solar system.”

After the membrane was adhered to the gypsum cover board, Pepco Energy Services of Arlington, Va., installed nearly 13,500 monocrystalline solar panels, covering almost 85 percent of the 480,000-square-foot roof.

The solar system required several thousand penetrations through the new TPO membrane. Initially, engineers considered caulking the penetrations, but again the convention center made a safer bet. It allowed GAF to provide custom-made TPO flashings for all the penetrations.

“We really felt the custom-made flashings were needed to provide longevity for this roof,” VanGent said. “Also, these details were required for our 20-year, NDL warranty.”

Architect Moore was also concerned about the wind resistance of the panels themselves. His firm helped design a four-bolt system for attaching the solar panels into the lightweight concrete deck. The resulting detail offered 4,000 pounds of pullout resistance per panel and a watertight seal for the TPO membrane.

Moore also questioned the impact resistance of the panels to debris from seagulls at the seaside location. “We needed to ensure that the panels, which are angled at 12 to 15 degrees, would hold up to strikes from anything dropped by gulls or other shore birds. We found that the panels were up to the task and able to sustain these impacts.”

Today, the 2.37-megawatt rooftop solar power system produces up to 26 percent of the convention center’s annual electricity requirements.

“Since the roof was going to house a solar array system, the owners wanted a white, reflective roofing system which would help to minimize rooftop temperatures for better performance of the solar panels,” said Jim Hagel Jr., senior project manager and estimator with Thomas Company.

Thomas’ roofing crews also did their part by adhering to a tough deadline. Roofing work started at the end of July 2008 and needed to be completed before freezing temperatures set in. Thomas had the roof membrane installed by Nov. 1, effectively beating an early New Jersey winter by a nose.

“We were very pleased to be involved with this historic project. You don’t get the opportunity to install a roof of this magnitude or importance very often, so when they come along, they are always special.”