Baltimore has so many vacant houses it is not even funny. Riding in on the MARC train you can see them as you come into the city. The parts of the city where I've been walking around, not so much the touristy areas, there are some noticeable vacant houses. Some just have boarded up windows, some have braces to keep them from killing pedestrians (cross the street anyways) and some of them are like the the house pictured, where the front, or the back or the roof is missing.
There are about 16,000 vacant houses in Baltimore City. There are a few houses one could buy for less than $2500 each. Yes, they are shells. Baltimore City government has a "Vacants to Value" program, some are shells, others serious fixer uppers.
At a point in time DC was like Baltimore is today. Shaw had a lot of vacant houses. Between the middle of the 20th Century and the end, Truxton Circle lost a lot of its population and experienced vacancies. Though I cannot find the internet proof, I know my house, where I live, was once a vacant property.
When we think of housing, decent housing, we think of places with roofs that don't leak, places with toilets that flush, spigots that run vigorously, and outlets that don't spark when you plug things in. DC and Baltimore both have a lot of old ('historic' if you want to be fancy) housing stock. Say what you will about gentrification, it gets the old houses fixed up (I'm ignoring the new construction). If not properly by the developer who slaps on a new coat of paint, the next homeowner or next developer who does a better job and addresses the lead pipes, the lack of central air, the so-so water pressure, and other housing emergencies.
Many vacants are not decent housing. The vacants listed at DC Vacant Properties have issues. 509 O St NW has so many problems, like being vacant for way too long, and legal issues, it is a nuisance just standing there. The row of yellow houses at 313-317 R St NW have had squatters but have water, mold and other interior damage and are not fit for safe living.
So lets go back to the house in Baltimore missing half of its front brick. It is a house. In theory it could house someone. In its current state it probably could kill the inhabitants by falling on them. In its current state it can't house anyone safely.