Floors 4 – 9 suffered partial collapse and/or fire damage as a result of the September 11 attacks . Floors 1 – 3 were not damaged . The building 's structural integrity on its upper floors were partially compromised due to the impact of steel and other debris from the North Tower . Other collapsed sections were due to fire damage . Portions of internal collapse and burnout were found on upper floors , mainly floors 6 – 8 . The black exterior facade suffered severe fire damage . Floors 5 – 9 were on fire after the collapse of the South Tower . A section of the fuselage from United Airlines Flight 175 landed on the roof . 5 WTC was the least damaged building of the entire complex . The Borders bookstore was undamaged after both towers collapsed . The building was the location of the Survivors ' Staircase , which was recovered from the building 's underground after it was demolished
United Airlines Flight 175
United Airlines Flight 175
5 World Trade Center