Add some floors? (Lois Raimondo/TWP)

That is not a new question. The future of the 1972 central library designed by famed modernist architect Ludwig Mies van der Rohe has been the subject of informal and official discussions for a solid decade, perhaps longer. The debate was rekindled this week by an outside panel’s review of options for a space long criticized for being dark, uninviting, expensive to maintain and otherwise unsuited to hosting a modern library.

The panel — engaged by the Urban Land Institute and composed of experts in development, architecture and marketing — looked at three options and presented its initial findings this morning. Two have been discussed in some depth before: A full-on renovation of the building to preserve its use as a central library (costing as much as $250 million), or moving the library elsewhere in order to sell the building (generating up to $70 million, if not more). The panel deemed renovation to be “not an economically feasible option,” given that it does nothing to leverage the value embedded in the building and downtown land.

The third option has not been the subject of much public discussion to date: making the Mies into a mixed-use space, with the library occupying about half of the 420,000 square foot building and leasing the rest to another tenant.

Under the plans presented today by the panel, the mixed-use option would involve adding a floor or two to the building — which is not as ridiculous or troublesome as it sounds. Mies originally envisioned a taller building than was built; the current structure could support additional floors; and there’s a case to be made that new floors would not be out of keeping with the tenets of his International Style.

The bigger question is, who else might occupy the building? And this is where money and politics start to muddy the picture. A boon of mixed-use would be that leasing the extra space at market rate (preferably to “knowledge workers,” one panel member suggested) would garner the city a revenue stream estimated by the panel at $4.1 to $5.5 million a year, enough to support loans to perform the necessary renovations.

But setting aside even a portion of what has been a wholly public asset for private use is going to generate objections from library and community activists. Some said today that they were not wholly opposed to a split use if the new use had a public benefit — for instance, a public school, a community college or an adult literacy center. But those uses wouldn’t throw off the cash of a market-rate tenant, making the finances a lot more tenuous.

In any case, a real plan for action is a long way off. The panel’s recommendations are not binding, and it will take some leadership from elected officials to find a way forward. Chief Librarian Ginnie Cooper is pressing city leaders to at least fund improvements to the building infrastructure that will be necessary no matter what happens — fixing elevators, HVAC systems, and so forth. Beyond that, someone is going to have to step up with a plan.

”The building is not going to improve unless something happens,” Cooper said today.

Below is the initial presentation given by the panel, which did its work in a five days of marathon sessions. A more comprehensive final report is expected in 60 days.