A new mixed-use project is under way on the booming North Williams Avenue-Vancouver Avenue corridor. The Cook Street Apartments, being built by general contractor Sierra Construction Co., will contain five stories of residential space over ground-floor retail space.

The project is due south of a New Seasons Market that was completed last year and developed by an affiliate company of Sierra, which also owned the apartment site before selling it to Seattle-based Lake Union Partners earlier last spring.

The LRS Architects-designed building’s 206 residential units will range in size from studios to two-bedrooms. Work on the project began in early June, and is slated for completion in December 2015.