As with Irving Trust, the famous neo-Gothic architecture of Chicago’s Tribune Tower (John Mead Howells and Raymond Hood)—with sweeping views from its upper floors and relatively shallow floor plates (ranging from 13,000 on lower levels to 1,800 square feet near the top)—made the 1925 skyscraper well suited to luxury-apartment layouts. Architects SCB transformed the tower into 162 condominiums of 56 unique layouts. Since the building’s population is lower in its residential incarnation, the architects shaped a more compact core, removing six of nine elevator shafts and replacing some with a relocated exit stair.

Conversion of the Tribune Tower’s base—a 65,000-square-foot assemblage of three buildings, erected between 1920 and 1950, in heights ranging from four to eight stories—required a different approach. There, SCB carved an 80-foot-wide landscaped courtyard out of the structures, stiffening steel column-and-beam connections to make up for the loss of lateral support. The courtyard left behind two wings on either side, narrow enough to host desirable residential layouts. The foundation’s load-bearing capacity allowed the addition of four floors on one of the wings, creating what SCB associate principal Steve Hub­­bard refers to as “very valuable” units.

DEEP-FLOOR DILEMMA

Large office structures with deep floor plates are particularly challenging to convert, because so much of their floor space is too far from windows to be desirable (or, in many jurisdictions, legal). These buildings, mainly from the 1950s through the 1980s, may have deteriorated fixed-glass curtain walls, unlike older towers that came with operable windows. If their potential can be unlocked, they can deliver a great number of units and take some of the least desirable buildings out of the office inventory.

Such conversions can entail removing building volume to provide more perimeter for capturing daylight, breezes, and views, as was done at the Tribune Tower’s base. In a speculative project in this vein, ARO proposed removing square footage from the bulky base of a 21-story wedding-cake setback tower completed in 1952 in Manhattan by Sylvan Bien. ARO placed the removed square footage atop higher floors, shaping new setbacks and terraces to add value to the apartments. Such radical reshaping is not as daunting as it sounds, says Yarinsky. “We proposed to add new loads where we assumed the load capacity already existed, in this way minimizing burdens on the foundations and structure.”

A similarly theoretical scheme was created by SOM for an ideas competition sponsored by the trade organizations the Steel Institute of New York and the Ornamental Metal Institute of New York. The brief called for the conversion of 1633 Broadway, a 48-story, 2.5 million-square-foot tower with deep floor plates designed by Emery Roth & Sons in Manhat­tan’s Times Square. “The sponsors selected about the toughest building for conversion they could find,” says Mahan. But its great size “also justifies significant massing and structural modifications.” The firm’s entry opened up the monolithic rectangular slab of the 1971 tower by cutting six courtyards in, strategically reinforcing the structural frame, and stacking the removed square footage in a stepped volume atop the building. The scheme diversified the incomes of residents by dividing the building vertically into adjoining condo, affordable housing, and co-living towers atop a base of commercial, institutional, and cultural uses. Like other competing projects, its ideas are speculative, but they broaden the spectrum of building-reuse possibilities.

Especially when converting buildings constructed since the 1950s, the exterior walls represent a particularly difficult problem. With expanses of fixed tinted glass and substandard energy performance, their curtain walls will probably warrant replacement with thermally efficient envelopes that include operable windows, a requirement for living spaces and bedrooms in many jurisdictions. But such retrofits, if the new exterior walls are highly insulated, can also allow mechanical systems to be considerably downsized, slashing energy costs, points out ARO’s Yarinsky.

To enable a greater number of conversions, cities may need to alter building codes and zoning regulations. New York is looking at reducing the size of required operable bedroom windows, as well as a currently mandated clear area around them, says Yarinsky, because many candidates for adaptation are unable to comply. Developers maintain that making such openings optional would render conversions more affordable. There’s pushback, however, from those who argue that rooms dependent on mechanical ventilation become uninhabitable in the event of power failures, and that the wellness benefits of light, air, and views of greenery should trump the cost consideration. “Must we return our buildings to Dickensian horror?” asks Ian Lomas, a principal at the Los Angeles office of Woods Bagot.

Other policies under consideration in New York, aimed at spurring more conversions of office buildings into housing—especially affordable housing—include changes that would allow residential development in parts of the city currently zoned only for office space and manufacturing, and the launch of an Office Conversion Accelerator program to help owners expedite projects. Meanwhile, in San Francisco, Mayor London Breed’s administration has issued a Request for Interest, asking downtown building owners and developers for conversion ideas for their underutilized building stock. The hope is to identify projects where the city could speed up or enhance such projects through zoning or regulatory changes. Similarly, in Chicago, the LaSalle Reimagined initiative, whose goal is to revive what was once considered Chicago’s Wall Street, includes incentives to hasten the transformation of office towers into residential buildings. Five developers and five properties (all but one built before World War II) were selected as finalists earlier this year. According to the city, the conversion projects represent nearly $1 billion in investment and will create 1,600 units, 600 of them affordable.

The Chicago program also has a retail component that would support street-level businesses serving the LaSalle corridor’s new residents while also addressing the post-­Covid loss of foot traffic. Qualifying businesses can receive grants for such projects as storefront upgrades, interior renovations, and design fees.

Of course, converting underutilized ­commercial properties not only has the potential to reinvigoriate once-lively downtowns and satisfy a huge need for housing, but, as Lomas, the Woods Bagot principal (who also worked in London), points out, there’s an importance to history. “In Europe, there’s always an assumption that what’s gone before has value,” he says. “There is an emotional connection. You add the layering you need to that.”

Supplemental Materials:

Arpit Gupta, Candy Martinez, Stijn Van Nieuwerburgh. ““Converting Brown Offices to Green Apartments.” National Bureau of Economic Research Working Paper 3150, August 2023. (Through page 4)