Since 1929, the historic and turreted Turnblad Mansion on Park Avenue in Minneapolis has housed the American Swedish Institute, a museum and cultural center. The stone mansion has also been bursting at the seams with a growing number of visitors and Swedish-themed activities. Plans to add on to the structure and expand ASI’s capabilities have been long in the works, and through a number of fits and starts with various architects.

But with Tim E. Carl leading a team of architects and planners from the Minneapolis firm Hammel Green and Abrahamson, Inc., which specializes in (among other practice types) cultural institutions, ASI is moving forward with a glass addition and mansion renovation that will give the institution room to grow on a full city block.

The 34,000-square-foot, glass-walled addition, called the Nelson Cultural Center (named for its benefactors, Carl and Leslie Nelson), will sport a roof of gray Vermont slate, as well as a green roof of growing and blooming plants. Inside the building, the glass will enclose a new lobby and café. The addition also includes a museum shop, art gallery, studio and crafts workshops, office space, collection storage, and a flexible event space with a wood-lattice ceiling like that of the timber roof of Stockholm City Hall and the interior of a Viking ship.

After a press conference announcing the design, Carl said he traveled to Stockholm to experience Sweden’s modern and vernacular architecture, and to have his early architectural designs critiqued by Stockholm architects. The addition will be connected to the renovated mansion via a tower, and the space between and around the two structures will be landscaped with perennials and birch trees that thrive in Sweden and Minnesota.

Three primary criteria drove the design, Carl explained. First was respect for the mansion, so that the addition refers and defers to the historic structure and the plan keeps the mansion as its centerpiece. Second was the wish to create “culturally meaningful spaces for gathering,” Carl said, through the used of well-crafted woods and stone. Third “was a deep commitment to sustainability.” The new campus will include 90 geothermal wells that will heat and cool the structure. The building has been designed to achieve LEED Gold certification, and the project will be completed in 2012.