CASE STUDY 1: MERCEDES-BENZ STADIUM ROOF

Project: Mercedes-Benz Stadium Roof
Location: Atlanta
Architect: HOK

The Project: The massive 2-million-square-foot Mercedes-Benz Stadium now eclipses Atlanta’s English Avenue and Vine City neighborhoods with its magnificent shadow. For 39 months, Mercedes-Benz Stadium rose from Georgia clay to a height of 30 stories, just 84 feet from its predecessor the Georgia Dome—but 300,000 square feet larger and with an increased seating capacity of up to 83,000. Deemed a multipurpose stadium, the new facility will be home to Atlanta’s professional football and soccer teams. In 2019, it will welcome the most important championship event in professional American football. But this structural masterpiece of the south will also host spectacular concerts and college football championship games.

The Design Approach: The Mercedes-Benz Stadium is nicknamed “the Pantheon” among the architectural community because of the way natural light enters through the roof and shines on the center of the field, inspired by the oculus of the ancient Roman Pantheon. Many have wondered why the Georgia Dome wasn’t refitted, having served as the city’s main stadium for 25 years. An architectural study commissioned by the Georgia Congress Center Authority, operator of the Georgia Dome, placed a price of nearly $550 million to refit it, as opposed to the new stadium’s total cost of $1.6 billion. Atlanta Magazine called it “the most expensive structure in Atlanta history.” The key wasn’t in cost; it was about investing in a stadium that had the potential to become culturally iconic, an architectural landmark. It’s perhaps the first time a building’s roof has been so celebrated inside and outside of the building community.

The Challenge: The roof of Mercedes-Benz Stadium, masterminded by the architectural firm HOK, is a feat of engineering so intricate and complex that its construction delayed the project for months. It is made of eight “petals,” each weighing 500 tons—equaling 8 million pounds. They are supported by 1.8 million pounds of trusses. When engaged, the petals open up in a manner similar to a camera shutter. The challenge was twofold—versatility and longevity—priorities that drove architects and contractors to make careful decisions at every step in the building process. The roof was constructed during the winter, creating environmental challenges. The construction team needed to build a roof designed for limited maintenance for an extended lifespan. The angled sections required complex installation with crews in harnesses and rigging due to the roof’s steep pitch, so avoiding premature reroofing was essential.

The Solution: In a project this monumental, when the cost of removing portions of the roof would be prohibitive, discernment and careful forethought guided every decision, including the choice of roofing boards. The Mercedes-Benz Stadium’s innovative architectural design called for a leading-edge roof board that could meet the roof’s performance and maintenance demands. The first two options considered were rejected by project designers due to concerns over sourcing, installation, uplift performance, and compressive strength. A glass mat roof board mitigated all of those concerns, fulfilled the project’s intricate construction requirements and aggressive schedule, and was ultimately the choice specified.

The Results: Each time this magnificent roof’s petals open, it releases cheers by thousands of fans at countless events; and when it is closed, it is expected to withstand nature’s ravages season after season for decades to come. The glass mat roof board is expected to continue to demonstrate why it’s preferred three to one by roofing consultants surveyed.

CASE STUDY 2: TARGET CENTER

Project: Target Center
Location: Minneapolis
Architect: KMR Architects

The Project: The Target Center in Minneapolis serves as the home for the city’s NBA team and countless concerts and many other large events. As a multipurpose arena, it hosts major family shows, concerts, sporting events, graduations, and private events.

The Challenge: When the City of Minneapolis needed to replace the nearly two-decades-old roof of this entertainment facility, it took a decidedly progressive approach. It sought to replace 115,000 square feet of the arena’s aging roof with a vegetative roof, bringing a long-lasting, ecological aspect to the facility.

The Solution: In order to add additional strength and extend the lifespan of the assembly, the roofing consultant included a ¼-inch glass mat gypsum cover board in his specifications. The cover board provides a uniform substrate that can handle traffic very effectively. While it’s not overly thick or heavy, the glass mat gypsum cover board provides excellent support, which is vital when considering the vast number of people—and products—that are moving over the system, especially during construction.

The Results: The roof assembly beneath the vegetated roof is expected to last up to 40 years, nearly twice that of a conventional roof.