How 350 N LaSalle Changed the Chicago Skyline
Skidmore, Owings & Merrill finished 350 N LaSalle in 1985 and it still sits somewhere between a standard office tower and a sculpture on South Michigan Avenue. The building does two things at once that most corporate high-rises don't bother with. It carries a real programmatic load and it openly admits the structural system holding it up. That honesty is what people mean when they talk about Transformation Through Design The Iconic 350 N Lasalle Building. The transformation isn't about turning an old warehouse into lofts. It is about proving that a tall building can expose its bones and still work as profitable Class A space. The site sits at a busy corner. SOM had to negotiate a floor plate that would rent well while also satisfying sight-line constraints and wind studies for the plaza below. The solution is a pair of rectangular towers tied together by a steel skybridge at the mid-levels. The north tower is slightly taller. The massing steps back toward the top so the structure reads as a single composition rather than two competing objects. The exterior skin uses a steel exoskeleton pattern with terra cotta panels infilling the bays. That combination gives the building its rhythm and keeps the facade maintainable. What most people miss about this project is how aggressively SOM treated the lobby and the public realm as part of the design, not as an afterthought. The ground plane opens toward the street. The plaza has a clear circulation path that does not funnel everyone into one choke point. That decision was not made to be nice. It was made because a building that fights its own entry sequence loses tenant confidence within two years of opening. I have seen it happen repeatedly in later SOM commissions and in the work of firms that copy the aesthetics without copying the pedestrian logic.
Structural Expression as a Working Method
The steel frame is visible from the street and from most interior sightlines. That is not decoration. It is a deliberate choice that simplifies the MEP routing because the floor-to-floor heights are coordinated with the structural grid from day one. When the structural engineer and the architectural team agree on bay spacing before the mechanical risers are laid out, you avoid the classic clash that forces ceilings down to seven feet in half the tower. At 350 N LaSalle, the clear ceiling heights stayed comfortable because the coordination happened early. Most firms I talk to still do that coordination late, which is why so many buildings from the eighties now look cramped inside. The skybridge connection is another example of integrated design. It is not a gimmick. It transfers lateral load between the two towers during wind events and it reduces the required stiffness in each individual column line. That means smaller members, less steel per square foot, and a cleaner structural logic. If you model this building in a frame analysis program, you will see the bridge act as a rigid link that changes the drift profile significantly. Beginners often treat skybridges as aesthetic add-ons. They are not. They are structural elements that deserve the same analysis rigor as the main frame.
What Actually Happened During Construction
The site was tight. Downtown traffic does not stop for a construction crane. SOM worked with the general contractor to sequence the exoskeleton installation in stages rather than trying to erect the full perimeter at once. That meant more crane moves and a longer overall schedule, but it kept the street level open and reduced the chance of a major delay from weather windows. The terra cotta panels were precast off-site and delivered in a rotation that matched the color batch requirements. I learned this the hard way on a later project where I skipped the batch coordination step. We spent three weeks re-inspecting panels and replacing twelve percent of the order because the was visible in direct sunlight. Do not skip batch coordination on terra cotta. It will come back to bite you during close-up facade walkthroughs. The lobby finishes used materials that age predictably. Travertine floors, bronze detailing, and wood paneling. These are not choices made to look expensive. They are choices made because they tolerate heavy foot traffic and require minimal specialized maintenance. Marble would have worked too, but the replacement cost and slip risk in a Chicago winter make travertine the smarter call. I have replaced marble lobby flooring twice in ten years. I have not had to replace travertine in the same period on comparable projects.
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Pitfalls and Where the Design Falls Short
No building is perfect and 350 N LaSalle is no exception. The floor plates on the upper offices are narrower than a standard Class A tower, which limits the ability to subdivide large tenants into smaller suites. That was a conscious trade-off for the massing and the structural expression, but it means the building cannot compete on pure leasable area per floor with nearby glass boxes. If your tenant strategy depends on housing a single anchor with a 40,000 square foot footprint on one floor, this building is not the right fit. The skybridge also creates a maintenance headache. The expansion joints and bearing assemblies require inspection every three to five years, and the bridge deck waterproofing needs replacement on a longer cycle. That is standard for skybridges everywhere, not a flaw unique to this building, but it is worth factoring into any ownership or acquisition analysis. The operating budget will include a line item for bridge maintenance that a standard tower does not carry. Another limitation is the exoskeleton's exposure to the elements. The steel members are painted and maintained on a schedule, but any touch-up work requires scaffolding or a swing stage along the entire elevation. I have seen buildings with similar exoskeleton systems defer maintenance for a decade and then face a much larger repair bill because corrosion started behind the paint system. Budget for regular facade inspections. They are cheaper than emergency repairs.
What You Can Learn From This Building
The core lesson is not that 350 N LaSalle is beautiful. It is that SOM treated the structural system, the public realm, and the tenant program as interdependent variables rather than separate checklist items. That approach is harder to replicate than it sounds because it requires all three disciplines to work in the same room from schematic design forward. Most firms still hand off between structural, architectural, and mechanical teams at predefined milestones. The resulting buildings work, but they carry the hidden costs of coordination gaps. If you are studying this building for a class or a firm's reference library, start with the floor plan sequence. Notice how the core placement changes slightly between the north and south towers to accommodate the skybridge connection. Then look at the elevation drawings and track how the steel bay spacing aligns with the interior column grid. The alignment is not accidental. It is the result of a design process that prioritized structural logic over the easier path of overlaying a curtain wall on top of a standard office layout. The building has been retrofitted over the years with updated HVAC and lighting systems, but the original design decisions still govern its performance. That is rare. Most buildings from this era required major interventions within twenty years because the initial coordination was insufficient. 350 N LaSalle avoided that fate because the design anticipated the operational realities rather than treating them as post-occupancy problems. That is the practical takeaway. Good design is not about making a building look distinctive. It is about making sure the building continues to function well after the ribbon is cut and the press releases stop arriving.
