James Lee Sorenson has begun building one of the first speculative office buildings along the Wasatch Front in years.

But the Utah businessman says he isn’t worried about finding tenants for the 120,000-square-foot building in Draper that is being constructed without a single signed lease.

“By the time we complete it, we will not only be fully leased but we will be turning people away,” he said of The Point II.

Sorenson isn’t alone in his optimism about the Wasatch Front’s office sector, which driven by corporate expansions seems to be in the midst of a turnaround after slumping during the downturn.

Sorenson, manager of Sorenson Group Management, is building one of at least four multi-tenant office buildings that are under construction totaling more than 481,000 square feet of space. There’s also the Old Mill IV in Cottonwood Heights, The Interchange in Draper and The Gateway 6, a building in downtown Salt Lake City that is fully leased even before it’s completed.

“It’s an amazing correction, when you think about it,” said Brandon Fugal, executive vice president of the real estate brokerage Coldwell Banker Commercial. “We’re seeing more cranes dotting our skyline than anywhere in the United States.”

Those cranes are following job growth, where Utah has remained in the top five among all states for some time.

Although office vacancies along the Wasatch Front remain high, they are at their lowest rate in three years, according to the Salt Lake City office of commercial brokerage CBRE.

At the end of 2011, the office vacancy rate in Salt Lake County fell to 15.3 percent, down from 17.1 percent at the end of 2010. In 2011, office absorption — the amount of space gobbled up by tenants that are expanding — rose to nearly 700,000 square feet, according to Tab Cornelison, CBRE first vice president. That’s double the absorption of office space in 2010.

Developers such as Sorenson are responding to the change in the market by constructing buildings to house expanding companies in need of more space.

That’s a fairly abrupt turnaround for a sector battered by the recession. Sorenson was ready to start construction on his Draper office building back in 2008, but by then it was clear the downturn that began in 2007 had begun to take hold. For much of the next three years, conditions did not support new construction.

Fast-forward to 2012, and a host of corporate expansions is fueling demand. Scott Johnson, founder of AtTask, a provider of project management software, has leased space in a five-story office building in Thanksgiving Park in Lehi to accommodate his company’s growth.

Even though AtTask might be better suited with operations in the technology-rich Silicon Valley — as many potential investors advised — Johnson said Utah’s lower cost of living and the state’s well-educated workforce convinced him to grow here.

“There are some definite advantages to doing business in Utah,” he said.

Several of the country’s largest corporations have made similar decisions. Much of the demand for office space along the Wasatch Front is fueled by the expansions of such companies as eBay, Adobe Systems, Goldman Sachs, Microsoft and IM Flash Technologies, a joint venture between chipmakers Intel Corp. and Micron Technology Inc.

Investors are taking notice of the expansion activity in Utah, according to a report by NAI West. Overall investment in Utah office buildings increased a whopping 281 percent in 2011, compared with 2010. Investment dollar volume last year — $121.8 million — was at the highest level since 2007’s $487.2 million. In 2010, investment totaled only $31 million.