On October 1, 1964, the NCPC approved the preliminary design of the FBI building. During the design phase, the architects discovered that the NCPC supported the FBI's desire for a highly secure building, and this influenced the structure's design significantly. The plans by Murphy and Associates called for an eight-story structure on Pennsylvania Avenue and a 12-story building along E Street. The two buildings were connected by wings along 9th and 10th Streets NW, forming an open-air courtyard in the interior. A portion of these wings would push underground into the hill which rose behind Pennsylvania Avenue. The building was set back from Pennsylvania Avenue. It also had underground parking accessible from 9th and 10th streets. An open deck, designed to allow pedestrians to enter on E Street and stroll along the second floor of the building, existed on the east and west sides of the FBI building. The architects noted that this deck could be extended on the south (Pennsylvania Avenue) side. The NCPC voiced only one concern. It worried that the "penthouses" atop the building (which were designed to conceal the HVAC and elevator equipment) were illegal. The penthouses raised the building's height to — higher than permitted by law.