The blaze apparently caused the collapse of much of the house in the 2600 block of 31st Street NW, the fire department said.
Houses on either side were damaged, according to the department. One suffered moderate damage, the other minor damage, the department said.
The cause of the fire could not be learned immediately.
The house was about a half-mile east of the Naval Observatory site and the vice president’s residence. Massachusetts Avenue and parkland separate the sites.