Adalberto Jimenez-Barajas, 19, is suspected of lighting the one-story wooden house in the 800 block of Boyes Boulevard in Sonoma on fire around 4:50 a.m. Sunday, according to the Sonoma County Sheriff's Office.
Barajas was arrested at the scene, sheriff's Sgt. Carlos Basurto said.
He was booked into Sonoma County Jail on suspicion of attempted murder, arson of an inhabited dwelling and child endangerment, and is being held on $1.1 million bail.
Barajas' ex-girlfriend and her father were not home when the fire started, but his ex-girlfriend's sister and the sister's two young children were asleep in the house at the time, Basurto said.
They were able to flee the burning house and were not hurt, he said.
Barajas was detained by the ex-girlfriend's family members and was arrested outside the house, Basurto said. He was taken to Sonoma Valley Hospital for treatment of a burn to his leg before he was booked into jail, Basurto said.
Barajas and his ex-girlfriend were together about three years before they broke up several weeks ago, Basurto said.
Sonoma Valley Fire and Rescue Authority Division Chief Spencer Andreis said an accelerant was used to start the fire on an outside corner of the house.
The blaze spread rapidly, and destroyed the roof and attic, Andreis said. The interior of the house sustained smoke damage, and firefighters pulled down ceilings to access the attic, he said.
Firefighters arrived at 4:52 a.m. and controlled the fire at 5:30 a.m. Damage is estimated at $100,000, Andreis said. He estimated the size of the home as 1,200 to 1,400 square feet.
Firefighters from the Glenn Ellen Fire Department and the Kenwood and Schell-Vista fire protection districts also responded to the blaze.