CHICAGO-The law firm Tressler LLP has extended its lease at Willis Tower, expanding by 10% to 83,000 square feet. The firm has been at the former Sears Tower building since the mid-1990s, and extended for more than 10 years, according to leasing agent US Equities Asset Management.

Tressler has about 175 attorneys and staff in the building. Mike Kazmierczak, an SVP with US  Equities, tells GlobeSt.com that he is seeing more expansion than consolidation in the past two quarters. “The trend has been to reduce, or to early extend, but we’re now seeing tenants lease more from a pure expansion need,” he says. Howard Ecker and Co. represented Tressler in the lease.

The building hasn’t suffered too much during the recession, signing more than 1.2 million square feet of leases in the 4.5-million-square-foot building since January 2009. The average asking rate is about $20 per square foot, net, Kazmierczak says.

The building also will compete with the rest of the dwindling supply of large block office space downtown. Kazmierczak says Willis Tower has one block of about 280,000 square feet on floors higher than the 40-story mark. Goldman Sachs now leases the space, but it will soon be available, he says. “There’s not much large block space left in the West Loop,” Kazmierczak says. There are reports that a few large-block users are examining the remaining vacancies, and there have even been whispers of possible new office building projects to meet some of this demand.