Post, Equitable Building. Interior iron structure exposed after a fire on January 9, 1912. The cast iron column is in the center bottom. Wrought iron girders frame into both sides of the column. Above the cast iron columns stands the built-up wrought iron column that supported the walls lining the lightcourt. (Landau and Condit, New York Skyscraper)

The second characteristic of Vitruvius’ definition of good architecture is “firmness,” that is, structural stability, something we naturally take for granted in our buildings.  I purposefully stated that we “take for granted” this for few people actually understand or appreciate the engineering skills and risks taken in the construction of a building, especially in that of a skyscraper.


In Section 1.10 I differentiated between “boxed” and “framed” construction as two different methods of erecting a building. With the few exceptions that I had noted, the construction of the interior structure of buildings prior to the 1871 Chicago and 1872 Boston fire was boxed construction: exterior walls of masonry (stone and/or brick) within which was erected a skeleton frame, be it of timber or cast iron.  Supported on top of this skeleton was some type of floor structure, the majority of which were wood joists and decking (the exact type of structure Jenney had used in the First Leiter Building), but Peter Cooper’s rolled wrought iron joists were slowing gaining a foothold in the market.  We saw a variety of floor structures being experimented with that included corrugated sheet metal arches with a concrete topping and George Johnson’s fireclay tile segmental flat-arched floors.  

Joseph Gilbert, Corrugated Sheet iron Floor Arches, c. 1865. (Wermiel, Fireproof Building)

And then the two fires occurred.  I can use the interior structure of the Equitable Building and the Western Union Building as examples of contemporary constructional techniques prior to the 1871 Chicago fire and the 1872 Boston fire.


George Post, Submission for the Equitable Competition, 1867. (Landau, George Post)

Although George Post had entered a design in the 1867 competition for the Equitable Building that was not chosen as the winner, as design work began on Gilman & Kendall’s winning design, it became obvious that the interior construction that they had envisioned would be cost-prohibitive and Post was commissioned not only to redesign its structure but also to supervise its construction.  The interior structure of the initial design reflected contemporary New York fireproofing practices as it was originally planned to have been entirely of masonry walls.  Although I have mentioned Post in the prior chapters, his background is now relevant to our story.  Post was born and raised in New York City, and after graduating from NYU with a degree in Civil Engineering in 1858, was one of the three students that Richard Morris Hunt had accepted in the first class of his atelier.  After having completed Hunt’s two-year program he partnered with a fellow student, Charles D. Gambrill that lasted until 1866, and by 1867 had, evidently, already gained a reputation as an expert with iron construction. 

James Bogardus, Harper and Brothers Publishing Building, New York, 1854. (Above)View of interior of second floor, showing the iron structure. Cast iron columns support iron composite girders, that support wrought iron girders, between which spring brick jack arches. (Gayle, Borgardus) (Below) Cast iron girder with wrought iron tie rod used in the Harper’s Building. Note the use of brick floor arches. (Bogardus, Cast-Iron Buildings)

By substituting the planned interior masonry walls with iron columns and beams, brick floor arches, (that varied little from the internal structure designed ten years earlier by James Bogardus in the Harpers Building) and lightweight brick partitions, Post succeeded in reducing the cost of the interior construction by almost half of its original estimate.

Post, Equitable Building. Banking Hall as it appeared in 1889). (Landau and Condit, New York Skyscraper)

In the last chapter I noted that Equitable had required in the competition program the inclusion of the two-story banking hall. Historian Sarah Bradford Landau has shown that Equitable had complicated the design of this area, however, with the requirement for a mezzanine to surround the 35′ wide by 105′ long banking hall, so that the bank’s managers could observe from their mezzanine offices their employees on the Main floor under the skylight, as well as so that customers could look up and view the managers.  The structural implication of this requirement was that the exterior masonry wall above the skylight that enclosed the offices above the mezzanine floor could not be continuous down through the banking hall, but would have to be supported by transfer beams either to piers or columns along the mezzanine so that it would open into the banking hall.  The columns in the first two floors of the Equitable Building, including those in the banking hall that supported the exterior walls of the lightcourt above were cylindrical cast iron sections with a 16″ diameter. The twelve columns in the banking hall were covered in scagliola (an artificial marble appearance formed by mixing finely ground gypsum in a matrix that is polished after it has set).  The floors were made of brick jack arches that spanned between wrought iron I-beams (no real change since the Harper and Bros. Building), that were supported on wrought iron girders that spanned between the columns.  


George Post, Western Union Building, New York, 1872. (Silver, Lost New York)

Post was then commissioned in August 1872, after the first Chicago fire, to design the ten-story Western Union Building. The site’s dimensions were such that no atrium was needed, therefore, Post’s structure was straightforward traditional boxed construction: exterior masonry bearing walls surrounding a framework of cast iron columns with wrought iron beams and joists, that supported a floor structure of brick jack arches leveled with a bed of concrete.  As an atrium was not needed, the interior structure was not as complex as was the structure for the Equitable Building.  In fact, there was no difference in concept between the Western Union’s interior structure and that of the Harper’s Building.  Was the fact that the Harper’s Building had been apparently successfully “fireproof” for this long of a period (18 years) the decisive factor in choosing to replicate it?  The decision to use exposed, unprotected cast iron columns following the experience of the Chicago fire, however, is somewhat surprising at this time, yet it is understandable given the operative theory at this time that a building’s interior was protected if the building’s exterior was completely fireproofed.  Peter B. Wight’s patented system to fireproof iron columns was still two years in the future.


Bogardus, James. Cast Iron Buildings: Their Construction and Advantages. New York, 1856.

Gayle, Margot and Carol Gayle. Cast-Iron Architecture in America: The Significance of James Bogardus. New York: Norton, 1998.

Landau, Sarah B. George B. Post, Architect.  New York: Monacelli Press, 1998.

Landau, Sarah B., and Carl Condit.  The Rise of the New York Skyscraper, 1865-1913. New Haven: Yale University Press, 1996.

Wermiel, Sara E. The Fireproof Building: Technology and Public Safety in the Nineteenth-Century American City.  Baltimore: John Hopkins University Press, 2000.

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