Flames blocked the only staircase in the home, located at 1208 Bay Road, but no injuries were reported, he said.
"This was a very difficult fire," he said. "We're very fortunate nobody was killed or injured, especially with people jumping out of windows."
One of the veterans told investigators he accidentally started the fire in the kitchen, Chief Schapelhouman said. He then quickly helped other people leave the board-and-care facility.
Residents jumped from windows or were assisted by neighbors and others leaving the building, and they were all evacuated before the firefighters arrived. The fire was reported at the 5,000-square-foot home at about 4:40 p.m. and controlled about 35 minutes later, he said.
The sprawling house, which was destroyed in the fire, had only one staircase despite its maze of 11 bedrooms. The fire spread to both floors and had burned through the stairs and the second-story floor.
"We're lucky nobody fell through," Chief Schapelhouman said. "You can't see that in the smoke typically."
Crews stayed at the scene all night and resumed investigations the next morning.
The 14 veterans have been relocated.
Forty-one fire personnel responded, including eight engines, two trucks and six chief officers, Chief Schapelhouman said.
Editor's note: Authorities originally said the group home was in East Palo Alto but later said it was just across the border in Menlo Park.