The little engines that could always seemed to find a home in Class B, brick-and-beam space in Boston’s Fort Point and Seaport neighborhoods. But now, they’re having a harder time than ever finding suitable space in the area – and their larger brethren are increasingly in a similar bind.

And as options shrink for both, rents are on the rise.

The vacancy rate in the local Class B office market, which comprises nearly 70 percent of the area’s 5.62 million square feet of supply, is just 8.9 percent, according to information from Jones Lang LaSalle (JLL).

“The ‘viable’ options in the Seaport for a tenant 10,000 square feet and under are limited,” JLL Research Analyst Sarah Daly wrote in an email to banker & Tradesman. “While one could find spaces under 10,000 square feet in about 13 buildings, these spaces range from being in Class A buildings to brick-and-beam style and span from the popular Summer and Congress Street addresses all the way down to Dry Dock. Therefore, assuming most tenants have a specific location and aesthetic they are seeking, many of these options would get taken off the table rather quickly.”

The Little…

One of the options almost completely off the table is 285 Summer St., the former home of architecture firm Payette. Until last March, the firm was the sole tenant in the 50,000-square-foot property. When Payette vacated the premises, building manager Aegean Capital was left scrambling to fill it up.

After common area renovations and tenant fit-outs, the property is already more than 50 percent occupied, said Peter Tilden, director of leasing for Aegean. And if the other three tenants that have committed to sign deals follow through, they will bring the property back to 100 percent full.

“All the interest was really surprising,” Tilden told Banker & Tradesman. “I was not particularly expecting the amount of activity that we got. By early summer we saw a tremendous amount of activity, and it just kept going through summer and fall.”

And that activity, coupled with constrained supply, is helping to push the neighborhood’s office rents higher. Tilden said rents in the area are pushing into the mid-$30s per-square-foot range in new leases, compared to the high $20s of the past. Tilden said Aegean was anticipating rents in the upper $20s a square-foot. And while he would not specify the prices the company is charging at 285 Summer St., Tilden said prices there “probably mimic the market.”

Brokers are expecting the rent appreciation to continue. With supply lacking for 10,000-square-foot and under tenants, there’s really nowhere for prices to go but up, said Patrick Nugent, assistant vice president at JLL.

But that rise will hinge upon new construction there in the area. New construction planned – at Seaport Square, Pier 4, and elsewhere – would likely command rents out of the price range for the ‘little engine’ tenants.

…And The Large

But the small firms aren’t the only ones eyeing the Seaport/Fort Point for a home. Banker & Tradesman has learned from multiple industry sources that LogMeIn, a computer technology company, is under agreement to relocate its headquarters into about 100,000 square feet at 320 Summer St. The property is owned by Lincoln Property Co., in association with ASB Real Estate Investments, and has undergone a major renovation, according to the source.

While no lease has yet been signed, John Miller, senior vice president for Lincoln, said “[LogMeIn has] tremendous interest in us and we have tremendous interest in them, and I think both parties would love to do something there.” The 320 Summer St. building will also include about 6,500 square feet of retail. Again, no lease has been penned, but there has been strong interest in that retail space from restaurant operators, Miller said.

“It’s a significant transaction because … it’s an example of rising rents in the Seaport,” one source said. “They’d have to be getting rents in the high $30s to low $40s per-square-foot, and the low $40s is probably more accurate. In the Financial District, they could have found the same size space in the mid-$30s a square-foot. But they want to be [in the Seaport area] because that type of space doesn’t exist in the Financial District, the open floor plan. And they want to be in that area.”

Additionally, shoe maker Converse – in the market for about 150,000 square feet – is seriously considering the Seaport. Online job search firm Monster.com is on the hunt for about 125,000 square feet; Zipcar and eBay are both looking for about 60,000 square feet; and EnerNOC, an energy efficiency firm, is seeking about 100,000 square feet. All are at least considering the Seaport area.

But just as the smaller tenants have few options below 10,000 square feet, the large tenants have few options for requirements upwards of 50,000 square feet. According to CoStar, One Marina Park Drive has about 246,000 square feet available; and One Harbor St. has about 67,000 square feet available. And sources tell Banker & Tradesman that other availabilities include about 75,000 square feet at 24 Farnsworth St.; 100,000 square feet at 51 Melcher St.; and about 100,000 square feet at Tower Point on A Street.

“Those are all good signs, with so many well-known tenants considering moving to the area, in large part because there’s such a buzz about the district, what’s happened already and what’s going to happen there in the future,” said Tom Ashe, senior vice president with Richards Barry Joyce & Partners.