High-rise roofing

• Photo courtesy of Georgia-Pacific Gypsum, Atlanta
• Photo courtesy of Georgia-Pacific Gypsum, Atlanta
• Photo courtesy of GA-MET LLC
• Photo courtesy of Georgia-Pacific Gypsum, Atlanta

The 52-story Georgia-Pacific Center in Atlanta is a city landmark. Built in 1982, the 1,112,000-square-foot commercial office building features a distinctive stair-step shape with a pink granite exterior designed by the architectural team Skidmore, Owings & Merrill LP, Chicago.

Approaching its 30-year anniversary, the tower's roof system reached the end of its busy and productive life. Having been patched and repaired many times during the years, it faced leakage issues. At one point, it housed window-washing scaffolding, but within the past decade the scaffolding no longer was needed and was lowered down a ramp and temporarily housed in a storage room. In addition to leaks, a solution to the water intrusion on the ramp had to be addressed. With winter around the corner, Georgia-Pacific Center's building-management team decided there was no way around it—it was time for a new roof system.

Sustainable design

Roof consulting firm Merik Inc., Marietta, Ga., was asked to assess the current roof system and design a replacement.

"Our main concern with the new roof system was wind uplift," says Pat Downey, Merik's president. "It's a concern for any high-rise roof, as well as the impact from foot traffic."

After a thorough inspection, Downey recommended design changes to address drainage issues. Looking to simplify the design, he added positive slope to facilitate drainage and chose Atlanta-based Georgia-Pacific Gypsum LLC's DensDeck® Roof Boards.

Ascending challenges

One of the reroofing project's most complex facets was the staging of the job site. In addition to the challenge of working on an occupied building, roof access was limited to one freight elevator to transport all materials. The logistics of moving old materials down and new materials up 536 feet required intricate planning.

Tip Top Roofers Inc., Smyrna, Ga., was selected as the roofing contractor to perform the roof system replacement. Tip Top Roofers managed the process by using only materials that fit inside the freight elevator. Materials went up the elevator to the 51st floor, where they were loaded onto an equipment hoist and moved to the roof.

In addition to challenging material staging, working in extreme winds 536 feet in the sky presented temperature and mobility difficulties.

"Getting materials 52 stories in the air isn't easy no matter how you do it," says Brandon Smith, Tip Top Roofers' vice president. "Some days, the winds exceeded 40 miles per hour and the temperatures never rose above freezing."

Stepping it up

The existing roof system consisted of 6-inch-thick concrete pavers weighing 300 pounds each, which covered a majority of the roof surface, along with No. 34 crushed granite over filter fabric, two layers of 2-inch-thick extruded polystyrene, a drainage mat and fiberglass-reinforced thermoplastic sheets.

"I've never seen a concrete paver that weighed 300 pounds used as roof ballast," Smith says.

Crews of eight to 20 people, depending on the day, removed more than 280 tons of concrete pavers. All concrete and debris were removed through the building by hand and recycled.

Raising a new roof system

One layer of torch-applied Firestone Building Products Co. LLC's SBS Poly Torch Base Sheet was used as a vapor retarder over the concrete deck, followed by a base layer of 1 1/2-inch-thick polyisocyanurate tapered insulation and one layer of 1/2-inch-thick DensDeck Prime™ Roof Boards attached with Firestone I.S.O. Twin Pack™ Insulation Adhesive. Two layers of torch-applied Firestone APP 160 smooth-surfaced polymer-modified bitumen base sheets followed by a Fire-stone APP 180 granular-surfaced cap sheet completed the system.

The ramp leading to the area that housed the window-washing equipment was sealed with a steel deck covered with 5/8-inch-thick DensDeck Prime Roof Boards and two layers of mechanically fastened 2-inch-thick polyisocyanurate insulation covered by 1/2-inch-thick DensDeck Prime Roof Boards attached using I.S.O. Twin Pack Insulation Adhesive. The membrane consisted of a two-ply application of torch-applied Firestone APP 160 and one-ply of torch-applied Firestone APP 180 white granular-surfaced polymer-modified bitumen membrane cap sheets to create a reflective roof.

"I'm confident the use of our DensDeck Roof Boards will give our new roof the ability to outlive the original roof system while contributing to our LEED® for Existing Buildings certification," says Todd Kuykendall, director of product management at Georgia-Pacific Gypsum.

Enjoying the view

The high-rise project began in December 2010 and was successfully completed on time in April 2011.

"The most rewarding part of the project was removing 280 tons of concrete by hand and transporting it down 52 stories without injury to any of our team," Smith says.

"We are happy with our new roof and are grateful we had such an amazing team working on the project," Kuykendall says.

Chrystine Elle Hanus is Professional Roofing's associate editor and NRCA's director of communications.

Project name: Georgia-Pacific Center
Project location: Atlanta
Project duration: December 2010–April 2011
Roof system type: Polymer-modified bitumen
Roofing contractor: Tip Top Roofers Inc., Smyrna, Ga.
Roofing consulting firm: Merik Inc., Marietta, Ga.
Product manufacturers: Firestone Building Products Co. LLC, Indianapolis; Georgia-Pacific Gypsum LLC, Atlanta