The St. Charles School Addition is located at 526 Renson Rd. in Hartland, WI. Hunzinger was selected to serve as general contractor for this 4,250 sq. ft. two story addition to the current school building. Zimmerman Architectural Studios of Milwaukee was the architect on this project.

The addition houses three classrooms upstairs that are used by students during the day and students in the Religious Education program several times a week. The classrooms also serve as gathering spaces for parishioners involved in different ministries.

On the first floor a dedicated, state-of-the-art S.T.E.M. Lab was built, providing students with hands-on and exploratory activities in Science Technology Engineering and Math. Also on the first floor is a new vestibule and entrance to the gymnasium, a concession stand area and new restrooms.