An aerial view of Boston's Downtown Crossing district. Image courtesy of BPDA

Asking rents for class B office properties in Boston declined by double digits while availability rates hit near-record highs of 22.3 percent.

While the class A office market has remained somewhat insulated from the downturn, with recent high-profile leases in new projects such as Winthrop Square and 350 Boylston St., class B properties have felt the brunt of the market’s pullback. Class B rents have declined 11 percent in the past year, according to a report by Colliers.

Boston has registered 777,000 square feet of negative absorption in the office market this year, including 522,000 square feet in the second quarter. Overall asking rents across both class A and class B space have declined from $62.84 to $62.49 per square foot over the past six months.

The vacancy rate in Boston’s nearly 67 million-square-foot office market ticked up from 14 percent in January to 15.6 percent at the end of June.

Class B availabilities hit 22.3 percent in the second quarter, and could prompt landlords to add more properties to the 3 million-square-foot pipeline of lab conversions already in progress, Colliers researchers Jeff Myers and Kelly Doonan said in the report.

Class A rents and occupancies have remained more resilient during the pandemic, with a 13.2 percent availability rate and average direct asking rents of $70 per square foot.

Availability rates range from a citywide low of 3.5 percent in the Fenway/Kenmore submarket to 25.5 percent in Charlestown.