U.S. employers added 6.4 million square feet of space in the first quarter, causing the vacancy rate to tick down to 16.6% from 16.7% the previous quarter, according to real-estate-research service Reis Inc. That is still relatively close to the 17.6% vacancy rate reached after the recession in 2010, and significantly above historical norms.

Rents also showed modest improvement, with prices sought by landlords increasing by 0.9% to $30.21 a square foot, up from $27.50 in 2010, according to Reis, which surveyed 79 markets.
With the labor picture continuing to improve, four-plus years of incremental growth is adding up to a relatively healthy office market, giving landlords newfound optimism.

“It’s not the best market I’ve ever seen, but it’s certainly on its way,” said Ryan Severino,an economist at Reis. “All of the signs are really pointing to a better future.”

As has been true for the past few years, the top-performing markets tended to be those where tech companies are fast-expanding. The San Jose, Calif., area, which includes Silicon Valley, saw rents sought by landlords jump 7.2% over the previous year to $28.03 a square foot, the fastest rent growth in the country. There, mature technology companies have been adding employees at a rapid clip.

Facebook Inc., for instance, is in the process of opening a giant Frank Gehry-designed expansion at its headquarters in Menlo Park, Calif., complete with a sprawling roof garden.

San Jose was followed in the ranking by Seattle, which posted a 6.4% increase in rents over the first quarter of 2014 in large part because Amazon.com Inc. has been adding space at an unprecedented rate.

San Francisco, a city where companies that were startups a few years ago are now leasing large swaths of space, was next, with a 5.9% increase. Uber Technologies Inc., for instance, in March leased nearly 200,000 square feet in a downtown tower, the latest in a series of recent leases that expand the company’s footprint.