When the Georgia World Congress Center (GWCC) in Atlanta added 1.6 million square feet, including a ballroom, two auditoriums, 29 meeting rooms and 420,000 square feet of new meeting space, owners knew they needed a roofing system on which they could rely. According to Jerry Lewis, the GWCC director of engineering, one drop of water in a booth can destroy the business of an exhibitor. It was not a chance the GWCC was willing to take.

"We take our roof systems very seriously," Lewis said. "We are an international convention center, open 24 hours a day, seven days a week, 365 days a year. For each exhibitor, we only get the chance to shine one or two times a year. The nature of our business requires we have and maintain very good roof systems."

After soliciting bids from several roofing contractors, Hardin Russell Mitchell, construction managers, in cooperation with Construction Services Inc., the roofing contractor, selected multiple Johns Manville (JM) roofing systems for the project. Denver-based Johns Manville had provided the roofing system for two previous convention center expansions.

Mike Yellott, senior estimator/project manager, of Construction Services, Alpharetta, GA said the project was not affected by higher asphalt prices, which began rising in 2001.

The exhibit hall was covered with a built-up roofing (BUR) system specified by the architect on the project.

"The system went down well and it has performed well. It was chosen because BUR was already on the existing portion of the building and it worked well."

A four-ply BUR system was selected for the 573,000 square foot exhibit hall and related areas and a gray UltraGard PVC SR60 single-ply membrane for the 150,000 square foot barrel shaped ballroom and main concourse.

For the BUR portion of the roof, two inches of polyisocyanurate roof insulation was mechanically attached to the metal deck. This was overlaid with Fesco Board insulation. Tapered Fesco Board pre-cut crickets were used between the drains.

After the joints were taped with fiber glass roof tape, four plies of GlasPly Premier felt were hot mopped in asphalt. The roof was finished with gravel. A DynaFlex modified bitumen sheet was used for the flashing details. Expand-O-Flash exterior covers were used for expansion joint openings.

According to Yellott, a gray PVC roof was selected to cover the barrel-shaped ballroom and main concourse because it would be visible from the ground and would be easier to install. The single-ply portion of the roof consisted of a 2.8 inch layer of ISO 1 polyisocyanurate insulation board over a metal deck. Tapered ISO 1 crickets and prefabricated roof drain diverters were used in various locations to assist with drainage.

Yellott said, "The way the (concourse) roof was sloped, it created quite a water flow and in order to manage that flow we put in the diverters."

Ed Stripling, senior associate Heery/TVS Joint Venture, said, "We added diverters every 30 feet to collect water in scuppers on the back side to minimize the amount of water that will end on the low side."

Stripling said another unique feature of the project was the 100-foot high glass walls that go past the roof edge. These were tied into the roofing system over the back of an aluminum framing system. A coping was used to cover it up.

Yellott says the project was one of the more challenging jobs that he has had to deal with in 30 years of contracting. "There was a lot of coordination and dealing with roof elevations and deck conditions."

He added, "The work on the new addition did not have any effects on the existing building, except in areas where we had to tie the new work into the existing conditions. That work had to be coordinated around the activities that were going on."

Near the end of the project, bearing pads were installed for more than 2,000 lightning rods on the building. According to Joe Dusek, senior project manager for Hardin Russell Mitchell, these were clamped down with adhesive.

Bill Smelcer, the general superintendent with Hardin Russell Mitchell in charge of construction of the new facility said the greatest challenge on the project was getting such a massive roof down in a timely fashion. This required schedule coordination. He said that both systems were easy to install and maintain. Kevin Clark, GWCC construction manager was instrumental in coordinating access to the facility to keep the job moving.

Smelcer had nothing but praise for the job done by Construction Services.

"They responded to tight time frames and they committed the resources to the job to respond to scheduling changes. They are very reputable, quality contractors," Smelcer said.