Willis Tower vs Promontory Apartments

Comparing the Willis Tower and the Promontory Apartments is interesting because they both rise in Chicago, IL, yet they were conceived by two different design teams, Skidmore, Owings & Merrill and Mies van der Rohe, and were completed at different points in time. They were finished over two decades apart.

This contrast within the same city allows us to see how different creative minds interpreted the evolving needs of Chicago across time.

Let's take a closer look!

The Willis Tower is clearly the larger tower of the two, both in terms of height and number of floors. It rises to 1450ft (442m) with 108 floors above ground, while the Promontory Apartments reaches 218ft (66.5m) with 22 floors above ground.

Of course, each project may have faced different briefs or regulatory constraints, which we don't really know about and could also explain the outcome.

Both the Willis Tower and the Promontory Apartments were designed in line with the aesthetic conventions of the International Style style.

The Willis Tower was designed at a moment when the International Style style was already in decline, making it more of a lingering expression of the movement. In contrast, the Promontory Apartments style was already in decline, making it more of a lingering expression of the movement. In contrast, the Promontory Apartments was built when the style still carried greater cultural weight.

The Willis Tower is primarily commercial, while the Promontory Apartments is primarily residential.

The Promontory Apartments offers 122 residential units.

Both towers share the same structural solution, a Frame system.

A frame structure uses a grid of columns and beams to carry the building's loads. This frees the walls from structural duties, allowing for flexible floor plans and larger windows.

However, when it comes to the facade, both buildings use different approaches. The Willis Tower uses a Curtain Wall facade, while the Promontory Apartments uses a Window Wall facade.

A Curtain Wall facade like the one seen in the Willis Tower uses a lightweight glass curtain wall hung from the structure, while a window-wall facade like the one seen in the Promontory Apartments uses panels fitted between floor slabs, leaving slab edges visible.