roof was a significant factor in the $392 million cost of the stadium. It allows the seating area to be heated warmer than the outside temperature when closed, allowing games to be played in inclement weather and in more comfortable conditions than an open-air stadium. For example, when it is freezing outside, the temperature inside will be . The idea of the stadium having a retractable roof had been considered right away in the initial design, as to help counter the unpredictable Wisconsin weather in the early spring and late autumn. The design team was appointed after a design competition in the mid-1990s. The architectural concept for the stadium was developed by the Los Angeles-based sports and entertainment team NBBJ, who worked closely with a Los Angeles-based team of engineers Arup, who were responsible for all stages of the structural and building services engineering design for the stadium, with the exception of the mechanical mechanisms that move the roof structure. The original versions of these mechanisms were designed by Mitsubishi Heavy Industries America as part of a design and build contract, but they have now been replaced by new designs after their failure. The executive architect responsible for the delivery of the final stadium design was a Dallas-based team of HKS, Inc. In addition to these major players there were a significant contributions from local teams including Eppstein Uhen Architects. The stadium design followed the trend of retro-designed ballparks with current amenities that began in 1992 with Oriole Park at Camden Yards in Baltimore. The original grass playing surface was installed on March 10, 2001, using County Stadium's surface infield dirt and home plate transplanted into the new stadium. The stadium was previously called Miller Park as part of a $40 million naming rights deal with Miller Brewing Company which expired at the end of 2020. Madison-based American Family Insurance purchased the naming rights in a new 15-year deal. Structural challenges The unconventional fan-shaped retractable roof has not been without complications. Major elements of the pivot system behind home plate and the outfield roof track have been replaced, even after the crane incident. At the end of the 2006 season, the roof's bogie system was replaced at a cost of over $13 million. The 10 new, , bogies were paid for with money from the settlement between the stadium district and Mitsubishi Heavy Industries of America. Six of the bogies