For David Leonard, president of the Boston Public Library, it’s all about addition. When you combine desirable things, like affordable housing and well-maintained public libraries, the sum is better than its parts.

Leonard appeared on Boston Public Radio on Tuesday to discuss a new initiative to add affordable housing in several library branches across Boston.

The West End and Upham’s corner branches will receive renovations and affordable housing units. A community-picked developer was recently awarded the Upham’s Corner project on April 13, and Leonard is optimistic the West End development will be approved soon. A third, brand new library will be built in Chinatown, which hasn’t had its own branch since the 1950s, said Leonard.

This initiative evolved out of former Mayor Marty Walsh’s administration which investigated what existing civic assets, from fire stations to parking lots, could help Boston’s housing problem. The current initiative is being led by the Mayor’s Office of Housing.

Combining housing with other public services like the library is called “co-location.” Having a large central library with a radio broadcast studio and cafe is one example of co-location, Leonard said, referring to the Newsfeed Cafe and BPR studio space.

The housing units built in the three libraries will all be various levels of affordable units with a combination of funding from the developer and the city. Renovations to the existing library spaces in the West End and Upham’s Corner branches will be funded by the city, which has shown commitment to these public resources. Mayor Wu’s $4.28 billion spending plan released last week includes the largest monetary commitment to public libraries in over a decade, said Leonard.

These three libraries will serve as a model to expand alternative affordable housing options. But Leonard said adding affordable housing may not be right for every neighborhood. Programming studies of the Field’s Corner branch revealed the space was too tight to deliver affordable construction; in Egleston Square, the community valued the existing greenspace over an expanded library/housing footprint.

Boston will become just the fourth city in the United States to co-locate public libraries and affordable housing. New York City, Washington, DC and Chicago have already implemented similar programs that Boston can model.

“We love to be first in Boston … but in this case we can certainly benefit from learning from our colleagues across the country,” Leonard said.

For these developments to work well, Leonard said there should be separate entrances for the library and housing, but be close enough so there is still a mutual benefit to residents. In terms of operations, Leonard said the library will be like a “condo within the overall development.”

Leonard said there has been an emergence of libraries valuing civic space. “This is just one more way we are adjacent to other civic infrastructure,” said Leonard. “Whether it’s a community center, a radio station or now — housing.”