Box 1-4 sounded at 2258 hours for a reported structure fire in the 400 block of S. 14th Street in the Allison Hill neighborhood. Squad 8 arrived with heavy fire on the second floor of a 2.5 story, frame duplex. A first alarm assignment was requested on arrival. Firefighters stretched lines into the fire building and exposure to make an aggressive attack on the fire. The fire extended to the top floor before the bulk of the fire was knocked down. The interior step from the 2nd to 3rd floor collapsed and command had all members evacuate the building. Extensive overhaul was required to extinguish the hot spots that smoldered in the void spaces. The fire was placed under control in about 45 minutes.