Office rents are so high that Bay Area businesses are buying buildings

Tenancy in the Bay Area means huge rent increases, fighting others for attractive listings and constant uncertainty.

And that’s true even if you’re a big business.

With rents spiking, deep-pocketed companies and public agencies are increasingly buying offices, for some of the same reasons home buyers plunk down for a space to live: more certainty over the long term on what they’ll pay for a roof over their heads.

The latest dealmaker: BART, which owns a sprawling network of rail lines but not its Oakland headquarters at 300 Lakeside Drive. Facing a rent increase of more than 60% there, BART’s board of directors approved on Thursday the purchase of a nearby building at 2150 Webster St. for a new headquarters.