TAMPA - Tampa office workers are about to get some much-needed elbow room.

Office developers, who haven't built much over the past few years, are rushing to construct office buildings to meet the pent-up demand from expanding local businesses. What's more, these new offices are being built as speculative buildings - spec buildings for short - which means developers are starting construction without firm commitments from tenants.

The flurry of new spec buildings is a show of confidence for the Tampa Bay area. It means developers and lenders anticipate that businesses here are growing and will continue to grow.

"It says that the economy of that area is doing well and that businesses are expanding, and that should signal job growth as these offices are filled," said Phillip Neuhart, an economic analyst for Wachovia Corp. in Charlotte, N.C. "As businesses invest and expand, office space is one of the commodities they need."

Commercial real estate services firm Cushman & Wakefield counts 642,600 square feet of spec office buildings under construction in Hillsborough County through the first half of 2006.

In comparison, the county saw only 100,000 square feet of spec office development in 2005, and 285,000 square feet in 2004. In 2003, Cushman & Wakefield recorded no new spec office buildings.

With 642,600 square feet of space on the books, 2006 is shaping up to be the best year for spec office development since 1999. That year, developers built 1.2 million square feet of spec office space, according to Cushman & Wakefield.

There's little doubt that office space is getting harder to find in the Bay area. Colliers Arnold, a real estate services firm, said the vacancy rate is 10 percent here, down from 11.7 percent a year ago. Vacancies in the West Shore business district, the area's largest office market, have fallen to 8.6 percent from 11.4 percent a year ago, according to Colliers Arnold. Vacancies are even tighter in newer buildings with high-end amenities - known in the industry as Class A office space.

Spec office developments can be found in two of the Bay area's biggest office markets, in the West Shore business district and along the Interstate 75 corridor.

In the West Shore area, Tampa-based Harrod Properties is building Cypress Bay Corporate Center, a four-story, 84,000-square-foot spec building in which the space will be sold as condominiums, instead of rented to tenants.

Nearby, Highwoods Properties has begun construction on Highwoods Bay Center, a seven-story, 208,606-square-foot building.

Dan Woodward, Highwoods' vice president in the Bay area, said the timing is right for a new spec building in the West Shore area because vacancy rates are shrinking and rental rates are rising. In addition, there's not a lot of land available for new development in the West Shore area, so developers don't have to worry about competing against a glut of new office buildings, he said.

Spec development "is not a guess," he said. "It's more of a calculated risk."

Also in the West Shore area, Crescent Resources LLC is hammering out plans for Corporate Center IV at International Plaza. Construction on the eight-story, 247,000-square-foot center could start in the first half of next year, according to Crescent's vice president for development, Ron Ruffner.

Across town, Duke Realty Corp. has nearly completed its Regency III office building in the Brandon area. The spec office building has found its tenant: Coca-Cola Enterprises will lease the entire 85,600-square-foot, single-story building.

Two more buildings are in the works at Duke Realty's Highland Oaks office park, near I-75 and East Dr. Martin Luther King Jr. Boulevard. Highland Oaks V, a three-story building with just less than 100,000 square feet of space, is under construction, and Highland Oaks III is still in the permitting stages.

"We're fully occupied at Highland Oaks, and we've had tenants that we weren't able to accommodate that needed to grow or that wanted to stay but couldn't," said Tim Hain, the company's senior leasing and development representative in Tampa.

Reporter Dave Simanoff can be reached at (813) 259-7762 or dsimanoff@tampatrib.com.