8.22. THE FIRST REAL USE OF EXTERIOR IRON FRAMING: THE WALLS OF THE LIGHTCOURT

Burnham & Root, Phœnix Building. South (rear) elevation. Demolition photo taken by Richard Nickel in 1959. The windows behind the four elevators that were supported by iron skeleton framing. (urbanremainschicago.com)

While the Phœnix Building’s Jackson Street elevation didn’t score big marks for consistency, the never seen rear elevation was a prophesy of one of the options available to rationally design the elevation of a skyscraper based solely upon expressing its iron skeleton construction (there was no need of arches with the iron frame).  Having studied the history of the early skyscrapers over the past forty years, I think that there was a greater interdependency than heretofore understood upon the two technologies that are always cited as having been responsible for the birth of the tall office building.  Some historians, like myself, claim it was the elevator that allowed the “skyscraper principle” to blossom, while others still maintain that a skyscraper needed to be iron skeleton-framed.  I am stating that it was the interdependency of these two technologies that manifested the first examples of exterior iron framing, at lease this seems to have been the case in Chicago.

George Post, Mills Building. Typical floor plan. (Gray, Elevator)

Once again, I have already shown that it was George Post who was the first to use the iron skeleton frame in the exterior walls of post-fire buildings.  This occurred in the light courts in the Mills Building and New York Produce Exchange (and most likely even the pre-fire Equitable Building: see Vol. 3, Sec. 2.12).  This was simply logical because these exterior walls were not at the building’s perimeter, and therefore, were not subject to the city’s building code pertaining to thickness or construction.  Therefore, Post was free to make these walls as thin and lightweight as possible. This was possible because he could still rely on the heavy exterior masonry walls to provide the necessary lateral stiffness. As these walls were not visible to the public (the Mills Building being somewhat the exception), Post had enclosed these walls with a minimum of effort and material, that also provided a maximum of daylighting.

Elevator historian Lee Gray’s research has impressed upon me the importance of providing light in pre-electricity elevators, especially daylight.  Although coal gas could be provided with a flexible tube, this was rarely chosen as the solution. The alternative was simply daylight, usually provided from a skylight at the roof in conjunction with light borrowed through glass placed in corridor doors and walls.  This method required that the elevator cab consist of a metal gridwork that minimized the obstruction of this light.  A more effective solution that was developed in Chicago was to build an exterior “window wall” at the back of the elevators.  This provided immediate daylight to the cabs at each floor. Coupling this with the need of a rigid iron structure within which the elevator cab could ascend and descend with minimum vibration, all the pieces were in place for the birth of the exterior iron frame. This may also have been the case in New York, but among Chicago buildings this solution first emerged in 1884 and continued as a favorite, at least with Root through the 20-story Masonic Temple (imagine that elevator ride!).

I have not focused on which architect was the first to construct this detail, and I’m not really interested in who it might have been, simply because George Post had already perfected exterior iron construction in the Mills Building and the Produce Exchange before any Chicago architect would attempt it (and it’s past the time to give him due credit!).  The two top contenders are Root and Jenney. Root has the more established claim with the Phœnix Building, but I think Jenney can also be credited with this detail in the Home Insurance Building. As both buildings were on the drawing boards at the same time, priority is hard to establish, and meaningless. Let’s first look at Root’s details in the Phoenix Building.  Donald Hoffmann had quoted Peter B. Wight’s 1895 statement about Root having been the first to use such detailing:

“[Jenney’s] Home Insurance Building is not an example of skeleton construction as now understood… The first building in which a complete skeleton wall was built, that I am aware of, was the Phenix Insurance Building… in which the rear wall, or about one hundred linear feet of it, is a complete skeleton construction, with enamelled (sic) brick on the outside, and a hollow tile wall on the inside. Each is supported on its own system of horizontal beams.  This… was the prototype of the court construction of the Rookery.”

I have traced Root’s use of a semicircular bay to contain a staircase (à la Peter Ellis’ design in 16 Cook Street, Liverpool) beginning with the Rialto in 1883/4. The Rand-McNally artist who drew these images was quite consistent and he drew the Rialto’s oriel as having a skeleton framed construction (which makes sense to me because Root appears to have copied the idea from Post’s Mills Building (see image above). One could speculate that Normand Patton may have been responsible for the use of iron framing in this portion of the building. The second version of this detail appeared in the Insurance Exchange of February 1884. The only image I have found of this design is from the Rand-McNally Guidebook of 1893 that, while it shows the semicircular oriel bay projecting into the light court, it is rendered as a bearing wall (compare it to the Grand Pacific’s light court) and not as an iron frame (compare it to those in the Rookery and the Rand-McNally Building below that are rendered as being iron-framed).

The Evolution of Designing the Elevation of an Exterior Wall in a Light Court. Bearing wall: #9: the Grand Pacific Hotel; Undetermined: #3: the Insurance Exchange, it appears as a bearing wall with windows; Skeleton Framed: #2: the Rookery and #4: the Rand-McNally Building. (Rand-McNally, View #1)

The shallow depth of the Phœnix’s site, a mere 46’ resulted in, once the depth of the single-loaded corridor office lightwell was subtracted, only a ten-foot depth for the lightwell.  This apparently posed a subtle challenge to Root in where to locate in plan the elevators and the building’s main stairway.  His, by then trademark projected oriel bay into a lightwell, in which he housed the central stair, was not repeated in the Phœnix Building.  Was it just too tight to try to push the oriel into the 10′ shallow space, or that an unsatisfactory daylighting performance would result from the over-stuffed lightwell as in the Insurance Exchange? 

Burnham & Root, Phœnix Building. Typical floor plan. (Hoffmann, Root)

Nonetheless, when confronted with where to put the elevators, and still be able to use the lightwell as a location for windows to allow the daylight to actually penetrate into the interior of the building and elevators, Root responded with a unique design.  He lined the elevators up against the lightwell’s long wall and put lightwell windows directly in back of the elevators, thereby allowing the daylight from the lightwell to penetrate through the elevator shafts and flood the interior corridor of each floor.  The shallow depth of the lightwell obviously did not require a skylighted atrium at the ground floor, but as one ascended in an elevator up through the alternating layers of masonry and views to the outside through the glass, who needed the choreographed sequence of an atrium?  

Burnham & Root, Phœnix Building. Lobby. Note the windows in the rear wall, in back of the elevators, that open into the lightwell. These were made possible by Root’s first use of the iron frame in an exterior wall. (Hoffmann, Root)

This decision tasked his engineering intuition to solve a delicate problem: the wall that he had just opened up to the maximum with windows, would also have to support the dynamic loads of the elevators moving up and down.  He solved the problem with employing the iron skeleton frame for the first time in a complete exterior wall in Chicago since the 1871 fire.  Earlier in the year, Cobb and Frost had used iron columns and beams in the first two floors of the Opera House, and Jenney had placed iron sections within the masonry piers in the upper floors of the Home Insurance Building, but no one had yet to construct a portion of an entire exterior wall from the foundation to the roof using only an iron frame.  Root would be the first to do so, and in doing so, would change the history of construction and architectural design.

Burnham & Root, Rookery. Structural detail of the light court curtain walls. Note the bearing shelf and web bracket cast with the column. (Thanks to Kevin Wilson at TGRWA, Nathaniel Parks at the Art Institute of Chicago, and Gunny Harboe for helping me to find this image!)

The columns were cast iron that were made with two projecting bearing shelf/web brackets (similar to how the Rookery was detailed as shown): one on the exterior face to support a line of I-beam spandrels, and a similar one on the interior face to support a second line of I-beams.  The exterior beams supported a kneewall of 41/2” thick white enameled bricks at each floor, and the interior beams supported a kneewall of 4″ hollow tiles at each floor.  The two layers of masonry were probably tied together at the window frame.  The existing photographs show that the exterior brick kneewall was continued vertically in front of each column.  As this elevation was merely the “back” of the building, little effort went into its design: it was detailed as a brick wall with square openings in it.  I will jump ahead a year or so and compare its design to how Root detailed the same situation in the Rookery. In the Phœnix, Root had detailed a continuous band of trim at the heads of the windows at each floor. One could assume that he had wanted to express the iron construction that held the masonry at each floor. Whether this was his intension or not, he did consciously design the Rookery’s lightcourt walls, as they would be visible to the building’s occupants, to express its construction: he added a sillcourse that interrupted the column covering from the spandrel panel, denoting that the masonry spandrel was the dominant feature that was continuously supported not on the columns, but at each floor.

Now let’s return to Jenney and the Home Insurance Building.  Its plan shows the same arrangement of elevators and iron framing.  I have searched for a photograph or an elevation of the building’s east (rear) façade to no avail. Fortunately, the Art Institute of Chicago has a good set of original drawings from which we can deduce the construction of this wall.

Jenney, Home Insurance Building. Eighth floor plan. (Tallmadge, Field Report)
Jenney, Home Insurance Building. View of SE corner. The nature of the light court walls is unclear. This shows the two-story addition. (Rand McNally view #5)

The only image I have located is this Rand-McNally view in which the nature of the light court walls is unfortunately hidden. I was lucky enough to find one of the floor plans that showed the actual cross-section of the piers in this façade.  This dovetails perfectly with a drawing of this detail contained in the 1931 Field Report.

Jenney, Home Insurance Building. Above: Section of the piers in the lightcourt (elevator core). Note that this drawing shows that the piers and spandrels had the same detailing as the exterior piers, i.e., cast iron lintel panels supporting the spandrel’s masonry. The only difference is that the masonry covering the iron section is only 4” thick because it is not subject to the building code because it is not in the exterior perimeter of the building. (Tallmadge, Field Report); Below: Plan of elevator core. Note the plan shows this exact cross-section in each of the piers. (Art Institute of Chicago)

The detail in the Field Report clearly identifies the exact same type of cast iron spandrel pan that Jenney had specified for the street fronts. Even the cast iron column is the same, including its being filled with concrete. The sole difference in the light court piers is the masonry covering is only 4” thick front and back versus in the street fronts it increased in thickness per the building code.  The light court was not at the building’s lotline and, therefore, was not subject to this code requirement.

Jenney, Home Insurance Building. Section through the lightcourt wall of the later addition. The section of the spandrel is at the far right. (Art Institute of Chicago)

I was also able to find in the Art Institute’s collection a wall section of the later addition of two floors, in which was shown the section of the spandrels in the light court. This mirrors the exterior spandrel at the far left, meaning that the elevation of the elevator wall was very similar to the exterior elevations.  Because the construction of the elevator wall, as I have just laid out, used the exact same structural detailing, we cannot make a claim, for the same reason I rule out the claim for the exterior, that the elevator wall was a true iron skeleton frame.  The final nail in the coffin of the legend of the Home Insurance Building for me, after studying it for the past 35+ years is this: no where in the Field Report is there any mention of spandrel beams in the framing of the light court. While the supporters of the Home Insurance Building claim that the intermittent transfer beams in the two street fronts could have been conceived by Jenney as spandrel beams, the fact that there are no such beams in the light court reveals that Jenney had not conceived of his iron framing as a frame. Case closed?!

For what it’s worth, the above discussion leads me to conclude that John Wellborn Root was, indeed, the inventor of the Chicago iron skeleton frame in the elevator wall of the Phœnix Building, recognizing, once again, that his “mentor,” George Post had been the first to use iron skeleton framing in a skyscraper. So can we all try to put the urban legend of Jenney and the Home Insurance Building to rest, once and for all? Please! It was in New York, and not Chicago where the iron skeleton frame and the skyscraper were invented.

Statue of Liberty under construction in Paris, 1883, Génie Civil, 1883. First image of the structure of the Statue of Liberty reprinted in the American Press, American Architect, September 1883. (Loyrette, Eiffel)

What I will document in the coming sections is the process of Chicago’s architects slowly and carefully replacing parts of exterior masonry walls with iron framing, one wall at a time, one building at a time, so as not to weaken the lateral rigidity of the building, until a building could be erected solely with iron framing. While Chicago’s architects were madly rushing in the spring of 1885 to complete these new buildings in time for the start of the new rental year, May 1, the French were exporting Gustave Eiffel’s example of just such a system of advanced iron technology in 214 wooden crates aboard the French frigate Isère directly to New York.  Eiffel’s structure arrived in the U.S. on June 17, 1885, but its erection had to wait until the pedestal, designed by Richard Morris Hunt was completed almost a year later.

FURTHER READING:

Gray, Lee E. From Ascending Rooms to Express Elevators: A History of the Passenger Elevator in the 19th Century. Mobile, AL: Elevator World, 2002.

Hoffmann, Donald. The Architecture of John Wellborn Root. Baltimore: Johns Hopkins University Press, 1973.

(If you have any questions or suggestions, please feel free to eMail me at: thearchitectureprofessor@gmail.com)

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