This is an expanded version of a previously posted story.
By Dave Boyce Almanac Staff Writer
An April 27 fire that significantly damaged a two-story house under construction in Portola Valley's Westridge neighborhood was likely caused by spontaneous combustion associated with materials used to stain exterior cedar siding, firefighters said.
The house at 10 La Sandra Way, now uninhabitable, was about a month away from being ready for occupancy, Battalion Chief Rob Lindner of the Woodside Fire Protection District said. The house was unoccupied at the time of the fire and there were no injuries, he said.
When firefighters arrived, about seven minutes after the 5:15 a.m. 911 call from a neighbor, they found one side of the house burning, Mr. Lindner said. The flames damaged about a third of the house, but there is smoke damage throughout, he said.
The fire started on the outside, climbed up the cedar siding from the bottom of the house and eventually made its way inside, Fire Marshal Denise Enea said.
The fire had been burning for at least two hours before firefighters got there, she said. It burned through 12-inch-thick timbers as well as a wall and a floor, both designed to resist fire for an hour referred to as "one-hour" walls and floors.
"That's kind of common when a fire gets going in the morning when no one is up and about," Ms. Enea said. "The saving grace was that the sprinklers were working."
Cedar siding on a house should not begin at the bottom of an exterior wall but three or four feet up, where it's much safer in terms of being ignited from the ground, Ms. Enea said.
"The fire did a lot of damage because it climbed up the side of the house," she said. "I tell homeowners, architects and contractors all the time that any kind of cedar siding, especially with the staining, is very combustible material."
The house's stucco siding was undamaged, she added.
"People don't think a fire is ever going to happen to them," Ms. Enea said. They take precautions against flu and traffic accidents and flat tires, but "when it comes to fire, because people don't see it so often, it's not something intimate," she said. "They never have to deal with it, so they don't think it's going to happen."
Using cedar siding "constitutes nailing kindling to your house," she said.
Fighting the fire
The house's first floor sits atop an above-ground garage. The fire burned through the first floor in places such that the underside of the second floor was visible from inside the garage, Mr. Lindner said. The second floor was not damaged, he said.
Crews from the Woodside and Menlo Park fire protection districts, and the California Department of Forestry and Fire Protection were on the scene. The one-alarm fire brought to the fire a total of five fire engines, one ladder truck, two battalion chiefs (to manage the operation) and an ambulance, Mr. Lindner said.
"The crews did a good job," he said. "(They) were aggressive to get it knocked down quickly keep it as that first alarm (level)."
Firefighters fought the fire from inside and out, and employed fans on a ladder truck to clear the scene of smoke, he said. They had it knocked down in about 30 minutes and extinguished about 15 minutes after that, he said.
The fire never threatened to ignite vegetation, but had there been wind, as was the case a couple of days earlier, "it would have been a whole different scene," Mr. Lindner said.