Willis Tower vs 7 World Trade Center

Comparing the Willis Tower and the 7 World Trade Center is compelling because they were both designed by Skidmore, Owings & Merrill, yet they stand in different cities (Chicago, IL and New York, NY), and were completed over two decades apart.

What this will allow us to see, is how the same firm's approach adapted to different places in different periods of time.

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 7 World Trade Center reaches 741ft (226m) with 51 floors above ground.

Willis Tower also offers more total built-up area, a total fo 4,499,999 sqf (418,064m²), which is about 2,818,882 sqf (261,883m²) more than what the 7 World Trade Center offers.

The Willis Tower also concentrates more floor area on its site, indicating a higher floor area ratio.

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.

The Willis Tower was designed in the International Style style, while the 7 World Trade Center reflects the principles of Contemporary.

The Willis Tower represents a late expression of the International Style, a style already in decline in 1974 when it was completed. By contrast, the 7 World Trade Center followed the then mainstream Contemporary, embodying the dominant architectural direction of its time.

With 32 years between them, the comparison also reflects how quickly architectural priorities can shift from one dominant language to another.

Both the Willis Tower and the 7 World Trade Center were designed to serve as commercial towers, and that has remained their main use since their completion, serving similar roles in the urban fabric.

Both the Willis Tower and the 7 World Trade Center rely on a Frame structural 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.

They also employ the same type of facade, a Curtain Wall facade.

A curtain wall is a non-load-bearing facade hung from the structural frame. It is anchored to floor slabs and transfers only its own weight and wind loads, allowing for sleek, glassy exteriors.