At about 11:10 a.m. crews were dispatched to a report of a fire at 84 Bay St., which is occupied by Casinghino Law Office. It also has one occupied residential apartment, fire officials said.
Crews arrived to find fire on the third-floor porch had burned through the railing and was extending to the building through concealed spaces below the porch floorboards.
Firefighters had to open up the concealed spaces to get at the fire, which was under control within about 20 minutes.
The historic building, once known as the Chandler House, is more than a century old and, due to its construction, can often be quickly consumed by fire. The total estimated damage is about $10,000, according to District Chief Michael Gamache.