Insatiable. That's the word investors and developers use to describe the appetite for new office development in downtown Calgary. The city's core absorbed a whopping eight million square feet during the last building cycle, cut short by the 2008-09 recession. The stragglers from that boom are just now opening their doors. Yet the city enters 2013 with a vacancy rate of only 0.5% for AA space, and an overall downtown vacancy rate of 5%.