San Francisco fire officials say the five-alarm blaze that tore through two residences began at the bottom of a trash chute in an alleyway.
The cause of Thursday's fire, however, remains under investigation. The blaze — the city's biggest in more than seven years — left more than 40 people homeless at the height of the holiday season.
Deputy Chief of Operations Tom Siragusa says the fire appeared to have burned undetected for a significant amount of time before firefighters arrived. Low humidity and high winds then made it difficult to control.
A Victorian condominium suffered an estimated $2 million in damage. A second building containing small apartments and studios sustained $6 million in damage.
A nearby charter school and another residence also suffered some damage.