Shadow Space Looms Over Downtown

150 North Riverside Plaza will open by early 2017.

CHICAGO—The downtown office market has been the picture of health lately, partly due to the in-migration of suburban firms and the expansion of the tech sector. But the market is approaching its biggest test in years.

Developers are finishing up a set of gleaming towers in the West Loop that will add about 3.6 million square feet of new class A office space over the next two years. Tenants are likewise readying their plans to move out of their current buildings, and if this shadow space remains vacant for any stretch of time, it will push the CBD’s vacancy rate upward for the first time since 2009, according to a new market report from MB Real Estate.