One proposal unveiled by Mecanoo and Martinez + Johnson Architecture called for a three-floor expansion with residential units on top to the Martin Luther King Jr. Memorial Library. That isn’t going to happen.

The District of Columbia Public Library has decided it will need more space than it originally thought in its downtown main branch, the Martin Luther King Jr. Memorial Library. And that means one possible configuration for its renovation and expansion—a proposal by the architectural team of Mecanoo and Martinez + Johnson to add an oblique three-story addition on top of the modernist box—is no longer on the drawing boards. After assessing the library’s needs, the Library board decided that it wanted more space for library programs, which has in turn changed its thinking about the mix of residential and commercial uses.

When Mecanoo and Martinez + Johnson won a competition to renovate and possibly expand the main branch, which has fallen into disrepair, among their proposals was a possible mixed-use building with a substantial residential component and a dramatic, contemporary addition turned on an angle from the main building. But that depended on the library making a decision about what the right mix of library and non-library uses should be.

When Mecanoo and Martinez + Johnson won a competition to redesign the Library’s main branch, they also included a one-floor option.

Now the plan is for a one-floor expansion, without residential units, and with more of the existing space devoted to library needs. The new top floor will include a terrace and areas for reading and other library programs. It also calls for a substantial increase in the amount of floor area the Library believes will be necessary not just to update and renovate the 1972 steel-and-glass box designed by Mies van der Rohe, but to create a 21st-century library with all of the new community and digital functions that libraries now routinely offer in the internet age. Two years ago the Library thought it would need 250,000 square feet of space, leaving it with as much as 150,000 square feet of space free for other purposes, even without an addition. Now it believes it will need all of the 400,000 square feet of the original building plus perhaps additional space in the new fifth floor.

That doesn’t preclude using some of the existing building for other purposes, such as a café, said Library spokesman George Williams. But he says plans haven’t been finalized for where or how much space that will entail.

In the original competition process, Mecanoo and Martinez + Johnson submitted both a one-story and a three-story option. Both routes present significant challenges when it comes to respecting the basic geometric integrity of the Mies original. The larger addition, and its offset angle, was likely to offer a clear visual distinction between the original and the new volumes. But it also created the possibility for mere dissonance between new and old. With a one-floor option the architects must now consider more nuanced questions, including whether it should be recessed and invisible from the street, or clearly articulated as an addition. The danger is a space that may seem like a roof-top executive suite or party pavilion set on one of the city’s most austere mid-century landmarks.

But as then-District chief librarian Ginny Cooper said when the Library selected Mecanoo and Martinez + Johnson last February, the choice was for an architectural team, not a particular design. Everyone expected that to evolve, and now it has.