SAN JOSE — A slender residential tower is in the works for downtown San Jose that will create a unique blend of affordable housing for senior citizens, along with retail and office spaces, and preserve a historic building on the site.

The 25-story housing highrise is being proposed for 19 N. Second St. in downtown San Jose and would feature a rooftop rotunda that would be a focal point in a gathering area for the residents, plans filed on Wednesday with city officials show.

The project proposal also would retain the historic building and add the tower behind the existing structure, said Kurt Anderson, principal executive with Anderson Architects and the designer of the development.

“We are playing off the existing historic building, playing off the nearby Bank of Italy tower,” Anderson said. “It’s a historic building, a historic district, and this is going to be eye-catching.”

The housing would consist of 210 units of affordable residences for seniors.

The lower levels of the development would create ground-floor retail in the historic building and three floors of offices.

Then, floors five through 25 would be residential, according to the development plans submitted Wednesday to city planners.

“You will have a mix of the new and the old, and that will make the project very interesting,” Anderson said.

A project that incorporates housing, offices, and retail in a single development is a unique approach to mixed-use development in San Jose.

“To have a thriving downtown, you need retail, offices, people living and coming into the downtown, you need all of those,” Anderson said.