The fire was reported shortly after 8 p.m. in a two-story office building at 1840 San Miguel Drive.
When firefighters arrived, they found heavy smoke and flames shooting up about 20 feet through the roof, Broschard said.
It took a total of 34 fire personnel from the county fire district and the Moraga-Orinda Fire Protection District about 45 minutes to bring the blaze under control.
The fire caused an estimated $200,000 in damage to the structure and another $25,000 to the contents of the building, but the damage could have been worse if firefighters hadn't taken aggressive measures to vent the fire, Broschard said.
Fire crews were able to salvage many of the contents of the suites on both floors while fighting the blaze, Broschard said.
No other buildings were damaged and nobody was hurt.
The fire appears to have started in a concealed mechanical space in the attic and roof area, and was not noticed until it burned through the walls and became visible from the outside, Broschard said.
Fire investigators returned to the building this morning to inspect the mechanical and electrical equipment in the area where the fire started.