The fire also burned a large amount of brush around the building, and firefighters were concerned because there is another house behind the burned structure, said Dale Fishack of the Smithsburg Community Volunteer Fire Co.
Fishack said it took 20 to 30 minutes to get the 8:32 p.m. fire under control. He said there were no injuries.
The building is at 11832 Paden Ave., near the intersection of Mapleville Road and Jefferson Boulevard in Smithsburg.
After the fire was extinguished, firefighters started pulling debris from the building as Deputy State Fire Marshal Ed Ernst stood by.
Ernst said he was starting to investigate the fire and added it was unclear if it was connected to other recent suspicious fires.
At 8:04 p.m., there was a report of a building fire at 82 S. Main St. in Keedysville, but Ernst said he did not have any information about that blaze.
Some brush fires also were reported Sunday night along Interstate 70 in Washington County, but Ernst said he did not know if any of those were connected to the suspicious fires. He said those fires could be caused by vehicles traveling on the interstate.