Over the past 30 years, the U.S. has added about 2 billion square feet of office space to its existing stock, most of which today’s highly mobile workforce no longer needs, at least not as a permanent home.

That vast built environment now inhabits the American landscape like a massive untapped natural resource. But no need for fracking. A startup called Liquidspace has turned to the core technology of the sharing economy, the app, to surface that hidden reserve.

Liquidspace CEO Mark Gilbreath doesn’t have an office all his own. Nor does his 26-person company, which he founded about three years ago.