Chief Harold Schapelhouman said the working theory is that the blaze started outside, then spread through a roof vent into the attic before destroying a bedroom and bathroom.
Although firefighters thought the one-alarm incident was over and left by 3 p.m., flames were burning inside a wall between two bathrooms. They returned to the scene about 46 minutes later after a salvage crew spotted smoke.
The chief said that thermal cameras had surprisingly not detected the second fire earlier, and thought that structural changes made inside the wall as a result of a recent remodel of the home may have somehow blocked the heat signature. Two firefighters remained at the home overnight to check hourly for other outbreaks.
He estimated total damages at $310,000 — and counting. "I suspect the numbers will get bigger rather than smaller," Chief Schapelhouman said.
No one was injured, but the family of four, along with two visiting grandparents, now faces the difficult task of finding long-term shelter and replacing necessities lost in the fire.
Neighbors reported hearing a "boom" shortly before 11 a.m. and seeing flames leap from a front corner of the home. Firefighters arrived on the scene about two minutes after the 911 call. They found themselves facing a fire that could potentially devastate the house next door, the chief said, which was roofed with "highly flammable" wood shingles. He encourages homeowners to look at other options for roof materials.
The house will be tagged as uninhabitable by the building department and PG&E will pull its meter to ensure that no one attempts to live in the home until it's repaired, according to the chief.
District investigators and insurance representatives should meet to compare findings within the next few days, he said.