Boston-based Berkeley Investments broke ground Thursday on Millbrook Lofts, a 100-unit apartment conversion at 9 Medford St. in Somerville.

The eight-story structure, built in a converted cold storage facility, will contain a mix of studios, one- and two-bedroom units, ranging from 500 to 1,300 square feet. Fifteen units, including five artists’ lofts, will be made available to qualified renters. Units contain exposed concrete ceilings and columns and contemporary finishes, including quartz kitchen counters.

The project is designed by architects Bargmann Hendrie + Archetype of Boston. Bowdoin Construction is overseeing the core and shell of the project while Reynolds Construction will work on the building’s interior. The building is expected to be ready for occupancy in late 2015.

Previous Berkeley residential projects include the Watch Factory Lofts in Waltham and the recently completed 625 McGrath in Somerville, which is 65 percent leased.