Deputy Fire Chief David P. Orth said a cigarette-sparked fire did about $20,000 in damage to an Alvarado Road home and its contents early Wednesday evening.
Firefighters got a call at 6:14 p.m. from a boy next door to the home and rushed to 139 Alvarado, where they found flames inside a second-story home office.
The blaze was under control within 20 minutes.
Meanwhile, Berkeley firefighters have been busy battling bigger blazes in Southern California, said Orth.
Two engines and eight firefighters were sent south as part of two Alameda County strike teams battling the raging wildland and forest fires that have devastated the Southland.
Both companies were originally assigned to fight the Buckweed fire in Los Angeles County near Magic Mountain amusement park.
One engine was later dispatched to the 9,000-acre Rice fire in San Diego County, and the second company was sent to combat the Grass Valley complex of fires near Lake Arrowhead in the mountains and near Big Bear Lake in the mountains above the Los Angeles basin.
Flames had been whipped into firestorms by Santa Ana winds, which died down Wednesday.
Orth said that he expects the two companies now in the south will be demobilized soon, though replacements may be needed depending on developments.