The Dallas-Fort Worth real estate market isn't built out of bricks and mortar.

It's jobs that keep the construction cranes swinging and homebuilders hammering out new subdivisions. As of October, D-FW was the top market in the country for year-over-year employment gains. North Texas has added more than 94,000 workers since a year ago.

Many of those workers filling up all the office space in D-FW are taking high-tech jobs, according to a new report by commercial property firm JLL. D-FW has been one of the top gaining markets for tech sector employment in the last five years, JLL found.

Companies in the area have added more than 32,000 tech workers since 2011.

Tech firms now account for almost 20 percent of total office leasing in North Texas. Almost 140,000 people in D-FW work in the tech sector, making this area one of the top five locations in the country for such workers, JLL found.

With tech firms taking such a big bite out of U.S. office space, real estate execs sometimes worry if it's too much of a good thing. They remember when the dot.com bust of the early 2000s left the industry awash in empty offices.

"Many people were burned during the dot-com bust, and the scars from that experience run deep," JLL analysts say in their new tech sector report. "Since 2009, the technology industry, the venture capital industry and many of us in the commercial real estate industry have been assuring the economy that this is not a bubble.

"The tech industry continues to be the largest consumer of office space across the country. They're gobbling up talent and large blocks where they can get them and driving economic growth from San Francisco to New York and everywhere in between."

In the last seven years, the D-FW area has added more office jobs of all types than any area of the country except New York City, JLL finds.

Companies have added almost 280,000 office jobs here since 2010 — more than Los Angeles, Atlanta, Chicago or Washington, D.C.

"This has been an amazing driver for our office market and has fueled 23 million square feet" of new leasing, said JLL managing director Jack Crews. "That's why our vacancy rate is close to its all-time low and why average office rents have increased 34 percent since the bottom of the last cycle.

"Corporate relocations have expanded the overall base of employment which has been a good driver for the multi-tenant buildings developed."