The adult daughter living inside the home quickly got in her car and drove to the nearest fire department to get help.
Investigators say the fire started in the garage and quickly burned up into the attic and across the whole two-story home.
A mother and father and their two adult children woke up to smoke and escaped, along with their dog.
Flames were shooting through the roof as the first of 50 firefighters rolled in. "It's problematic, especially the access is a major issue. You can only fit a couple of engines up there, but the first couple companies really are the ones that stopped it," South San Francisco Fire Department Battalion Chief Brian Metcho said.
By morning the devastation was overwhelming as the family tried to retrieve some belongings from the rubble in suitcases and boxes.
During the fire, the owner burned his hand on a super-heated door to the garage as he escaped.
The adult son told ABC7 News they wanted privacy as they sort things out, but said they are grateful to have friends and family to stay with now for the holidays.
Investigators say this fire was an accident, but have not pinpointed the cause.