SANTA ROSA (CBS SF) — A vacant Santa Rosa commercial building was heavily damaged late Thursday after flames from a nearby homeless encampment spread the structure, authorities said.

Santa Rosa Fire said crews were dispatched at 11:52 p.m. to reports of a structural fire in vacant building at the intersection of Sonoma Ave. and South E St.

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The first arriving crew found a large commercial building with fire showing from the side and roof. Crews worked to attack the fire from the side of the building and the roof.

The building was last occupied by Burbank Housing and was completely vacant.

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Firefighters quickly knocked down the exterior fire and made entry into the building. There was heavy smoke throughout with fire extending up the exterior wall and into the roof structure.

Firefighters searched the building for occupants but none were found. They accessed the roof through ventilation holes and extinguished fire in the façade.

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Cause of the fire appeared to be a homeless encampment fire causing structural damage. Damage was estimated to be $100,000.