Persistent heating inside the soffit degraded the wood trim, lowering its ignition temperature, he said.
Petaluma's ladder truck delivered firefighters to the roof, where they cut holes to make sure they had extinguished all the flames, Holden said.
The adjacent hair salon was back in business by about 5:25 p.m., but the restaurant, which features California-Mediterranean cuisine, will be closed indefinitely.
Tony Najiola, the restaurant's owner and chef, said he did not know when he would reopen.
"It doesn't look like we're going to be grilling food any time soon," he said, standing across an alley from the back end of the building.
Najiola, sipping a flute of champagne, took a philosophical approach to his situation. "What are you going to do?" he said. "Today is bad; tomorrow might be good."
"Me and my staff do a good job," the New Orleans native said. "We'll get through this."
Central Market, opened in 2003 at the intersection of Petaluma Boulevard and Western Avenue, has drawn positive reviews from local and Bay Area critics.
Holden estimated the damage at $50,000 to the building and $20,000 to the interior, including equipment.
Any fire in Petaluma's historic downtown is a concern, he said, due to the area's economic importance.
City Councilman Mike Harris stopped at the scene and complimented the firefighters' efforts.
"All things considered, it went pretty well," he said.
Eight engines and a ladder truck responded to the fire, with the Wilmar, Gold Ridge, Rohnert Park, Rancho Adobe, San Antonio, Cal Fire and Two Rock departments assisting Petaluma at the scene and providing backup at city fire stations.
Barbra Long, co-owner of the adjacent Finesse Hair Salon, said there were five customers in chairs — four with black dye on their hair — when the evacuation was ordered.
Some smoke entered her shop, but there was no damage.
"It was OK," she said. "It wasn't scary."
(Staff Writer Lori A. Carter contributed to this report. You can reach Staff Writer Guy Kovner at 521-5457 or firstname.lastname@example.org.)