Firefighters responded to a home in the 2000 block of Parker Street shortly after midnight after a neighbor reported seeing a fire burning on the home's back patio, Fire Marshal John Fitch said.
Flames had spread to an exterior wall of the home and climbed up to the roof, but firefighters were able to extinguish the blaze quickly, he said.
The home's residents had been woken up by neighbors and got out of the house safely, he said.
The one-alarm fire was initially considered suspicious because there was no obvious ignition source.
Then, Fitch said, "The woman remembered that early that morning, she had taken out some ashes from the fireplace and put them in a paper bag and put it on the patio."
The blaze caused an estimated $100,000 in damage, but "it could have been much worse," Fitch said.
He reminded residents to be extremely cautious when disposing of fireplace ashes, and recommended that ashes be watered down and placed outdoors in a metal container with a lid for a day or two before they are thrown away.
"It's a good lesson learned," he said.