A new breed of user, combined with growth from existing tenants, will emerge to finally absorb the pesky 3.33 million square feet of available low-rise space in Boston’s high-rise office towers, according to industry experts.

There is about 5.3 million square feet of available tower space in Boston, according to information from Jones Lang LaSalle, the vast majority of which sits below the 16th floor. That low-rise space formerly provided workspace for the back offices of the region’s most powerful financial services companies, law firms and insurers – jobs that have since been shipped to cheaper digs, if not eliminated entirely.

This outsourcing has created a bifurcation in the tower market in recent years. Space on the more prestigious upper floors – the spaces with million-dollar views and client-wowing cache – have experienced strong demand and are fetching healthy rents. But that demand hasn’t trickled down (literally) to lower floors, where vacancies persist and rents remain anemic.

Supply & Demand

But a new generation of users is emerging, including companies like Watertown’s Communispace and Cambridge’s Brightcove – both relatively young, value-seeking, high-tech companies taking 80,000 square feet apiece in the lower portions of Boston Properties’ recently completed Atlantic Wharf development, according to industry sources.

And one broker said a dominant force in absorption will be tenants already housed in the towers that will need to grow as the economy slowly recovers.

“Tenants eventually will come from right where they are – in the buildings,” said David Martel, executive director for Cushman & Wakefield in Boston. “With so much corporate consolidation, we think the tenants are eventually going to grow.”

With little new construction on the horizon, Martel and his team believe the law firms, accounting, and other financial services companies will step-up to fill the space once new jobs are created.

“With a lack of new supply, as long as we have modest absorption, all spaces are going to have to lease,” Martel opined.

But existing tenants will not consume nearly enough of the millions of square feet of available low-rise space to be the most important driving factor in the tower market, according to others.

Benjamin Heller, executive vice president for Jones Lang LaSalle, said the alternative users that will move into the city for space include high-tech firms looking for more affordable offices than they can find in Cambridge, and others that want a Boston address but have not been able to afford downtown prices in the past.

“The types of tenant to absorb that space will be different than previously occupied it,” said Benjamin Heller. “Many will come from Cambridge and the suburbs, which we’re already starting to see.”

One downtown landlord said it will be a mix of both new and traditional tenants that will eventually fill space in the bottoms of the towers. Don Chiofaro, Jr., project manager at The Chiofaro Cos. and the man in charge of the leasing and marketing of International Place, said a variety of prospective tenants – including financial services companies, law firms and architects – have all shown interest in the lower floors of his towers recently. But there is no denying the trend of tech-oriented Cambridge companies and others that have moved downtown, he said.

But he acknowledged that filling the largest vacancies in existing towers will take some time.

“The real large low-rise floor plates, the 50,000-square-foot plates, are going to be the last spaces to go,” even though those floors have already been leased at new developments like Atlantic Wharf, he said.

Urban Opportunities

More than 400,000 square feet of space is expected to be taken in the next year by companies that never had a presence in the downtown market. And while there are new users moving into the city already, they are opting for the limited new construction that has occurred and not existing towers, so it could take several years to see significant absorption in the low-rises. So there will not be a glut of leases signed, but as leases roll, users currently in Class B buildings could eventually start looking for affordable rents in more elite locations, albeit on those lower floors.

“It’s almost like back office, where you can put some of your grunt workers,” said David Begelfer, chief executive officer of NAIOP Massachusetts. “But those buildings still are prestigious to have as an address. Those rents [in the mid-$30s per square foot] obviously are a little more depressed than the higher tower space, and that creates opportunities for some companies to trade up as far as address is concerned. You play a little musical chairs and trade up for location.”

For the next year or so, low-rise space will see a flat market without rent growth, according to Cushman’s Martel. But eventually, without much new supply, “people will look up” and vacancy rates will be back to normal, he said.

“I think everybody’s curious to know where the demand is going to come from today, there are lots of changes in the financial services industry tight now,” Brian Smallman, vice president in the downtown brokerage group at Lincoln Property Co., told Banker & Tradesman. “There are suburban firms looking to come downtown, and some Cambridge companies. It’s a little hard to say what sector is going to be hotter in the next five years going forward.”

But many companies still have shadow space to absorb before they can think of taking additional square footage, he added.