CHICAGO—The vacancy rate among the CBD's top office properties has finally started to tick up as many tenants left behind empty spaces after moving into downtown's newest trophy buildings. That was the conclusion of researchers from MB Real Estate, who just released their latest index report, which examines the CBD's 30 newest class A buildings with more than 300,000 square feet. This set of buildings, which contains some of the CBD's most desirable space, serves as a leading indicator of office market conditions.

Direct vacancy in the index buildings increased by 83 bps to 11.4% percent. Meanwhile, the CBD's overall direct vacancy increased to 12.2% at the end of the third quarter of 2017, a 67 bps increase from the previous quarter.

The opening of 444 W. Lake in the fourth quarter of 2016, and the January delivery of 150 N. Riverside, added two new structures to the company's index. The properties, where leasing has been quite robust, replaced 227 W. Monroe and 35 W. Wacker, both of which were built in 1989. This also decreased the index's total square footage to 26,906,233 out of the CBD's 135,391,152.