When people talk about Baltimore’s vacant real estate, they’re usually referring to the blocks of dilapidated rowhouses in some of the city’s hard-hit neighborhoods. But there’s another kind of structure that worries city planners:  the 1970s-era office tower.

“Several Downtown buildings do not meet today’s standards and are considered functionally obsolete for office use, even with substantial investment,” according to the Office Vacancy Task Force. Which is a big problem, since Baltimore’s tallest building — 100 Light Street, the former Legg Mason building — is one of those outdated models. “Stuck in between the perceived coolness of early 20th century facades and the newness of all-glass towers,” Mark Byrnes writes in the Atlantic Cities blog, “these buildings are having a hard time retaining existing tenants, let alone attracting new ones.”

Another worrisome structure is 2 Hopkins Plaza, built in 1970 and smack in the middle of the Inner Harbor. It’s currently 42 percent vacant, and that’s including PNC Bank, which is scheduled to move out this summer. Some developers hope that renovations and mixed-use use residential conversions will save the buildings. Or does something more drastic need to be done?