At the beginning of this Chapter I started with Root inventing the iron-reinforced concrete foundation.  This was only one of a number of construction innovations involved with this building, and I believe we can credit this to the mutually-reinforcing relationship between the two former New Yorkers, Root and George Fuller (Root was less than a year older).  Root’s family had moved to New York following the end of the Civil War, where he had returned following his graduation from “high school” in Liverpool.  He had enrolled in and graduated from what would become NYU in Engineering, the same technical training that George Post had experienced twelve years earlier.  Root was attending classes while Post was completing the innovative Equitable Building, that you know I claim to be the first skyscraper.  Knowing architecture students like the back of my hand, Root would have been studying every detail in that building.  Root had left for Chicago in early 1872, four years before George Fuller was named the head of the New York office of Peabody & Stearns.  His last project before he left Peabody & Stearns to set up his own firm in Chicago was the United Bank Building.  

It is critical to note that during Fuller’s two years in New York, Post was erecting the New York Produce Exchange, a building for which we have photographic evidence proving that its light court was completely iron skeleton-framed and enclosed with an masonry and glass curtain wall.  To summarize an earlier chapter, if we discount the Equitable Building as the first use of iron skeleton-framing in its light court because of lack of hard evidence, than by default, Post’s Produce Exchange (1880-1) deserves that honor.  So in 1885 in Chicago we have Root, having studied Post’s structure in the Equitable building, and Fuller, having just arrived in Chicago after having watched the construction of Post’s Produce Exchange and having completed the construction of the Opera House Block, combining their talents and knowledge of Post’s detailing of iron framing to erect the Rookery.  No one should be surprised that the result would be the first use of iron skeleton framing in a Chicago building, inspired by Post’s pioneering efforts with iron framing in New York. (Note that iron skeleton framing was first developed and used in New York, not Chicago.)

Burnham & Root. Left: From left to right: Phoenix Building, Traders Building, 305 S. La Salle, Commerce Building; Right: Commerce Building, 319 S. La Salle, 1885. (Hoffmann, Root)

But before we can start erecting the Rookery’s iron, we need excavation and the foundations.  In November 1885, excavation finally began on three projects designed by Burnham & Root: the Phoenix, the Commerce Building, located immediately south of the Phoenix, and the Rookery.  Although the weather in November and early December of that year was exceptionally mild, it was only a matter of time before cold weather would once again mark the traditional end to the year’s building season.  But Root/Fuller’s ingenuity was again sparked by this challenge, resulting in a solution that defeated winter, the age-old nemesis of the contractor, once and for all.  Each of the construction sites was covered with a wood-supported enclosure heated by portable heaters.  This kept the temperature within the enclosure above freezing, permitting the construction of the foundations to proceed throughout the entire winter season.  Root’s matter-of-fact explanation of the technique at the February meeting of the Illinois State Association (WAA) the belied the revolutionary nature of his invention:

“We adopted the cover over our foundation work also under necessity, as the work had to be rushed and we could not allow the weather to interfere.  The shed over the foundations for the Phoenix building on Jackson and Clark streets, cost less than $1,200, and about one half of that will come back in lumber which can be used for scaffolding, etc.  The shed is perfectly lighted and a few salamanders keep it perfectly heated.”

However, other Chicago professionals recognized Root’s achievement in his liberation from the grasp of Father Winter.  Dankmar Adler, following Root’s talk, paid homage to Root’s technical genius.

“A method has been introduced of using T rails and concrete in foundations which has become generally used in the large buildings now being erected.  Mr. John W. Root is present, and as he has large experience with this method as well as with construction under cover, he could perhaps give valuable information and data on this subject.  In regard to Burnham & Root’s construction of foundations in winter under cover they deserve great credit, in the same degree as is awarded to the man who causes two blades of grass grow where one grew before.”

Typical floor plan of a double-loaded corridor scheme for a site with a width greater than 100’ compared to a single-loaded corridor on a site with a width less than 100.’ (Drawing by Kyle Campbell)

If the exterior design of the Rookery presented Root with a challenge similar to the Burlington Building, the problems in the design of the interiors of the two buildings could not have been more different.  Whereas the Burlington’s plan was a doughnut with a single-loaded corridor, the Rookery was a doughnut with a double-loaded corridor.  The difference is obvious: while the Rookery’s inner ring of offices needed direct exterior exposure for daylight and natural ventilation, the Burlington’s cantilevered balconied hallways had no such need.  Root, therefore, could put the Burlington’s skylight that enclosed its 55′ by 75′ central atrium at the roofline, creating a tall, invigorating space filled with daylight and five stories of motion.  In the Rookery, however, in order to allow exterior air and light to reach the inner tier of offices, Root was forced to pull the skylight all the way down from its lofty height at the roof to the point where it hovered, somewhat menacingly, over the 62′ by 71′ atrium at the relatively low level of the third floor.  This was the same solution that Boyington had used fifteen years earlier in the Grand Pacific Hotel, located on the opposite side of Quincy Street. 

Left: W.W. Boyington, Grand Pacific Hotel, 1870. Section showing the skylight at the second floor and the light court above; Right: Burnham & Root, The Rookery, 1885. Section showing the same type of skylight and light court. (Left: The Land Owner, April 1870; Right: Chicago Architecture Foundation, The Rookery)

As these two sites had the same dimensions, the design problem was the same as well, a double-loaded corridor doughnut plan. thereby the solutions should have been similar.  And they were, with the exception that Root, fifteen years later, had a more developed iron framing technology to employ. Where Boyington had used masonry bearing walls, to support the walls of the lightcourt that Root had also employed in the walls lining the Burlington’s atrium, Root now used the Rookery’s light court to experiment with using the iron skeleton frame to support an exterior wall, the first such example in Chicago.  While the Rookery’s exterior walls were still required by the building code to be a masonry bearing wall (if anyone knows how the curtain wall in the two alleys were permitted, please let me know!), the exterior walls of the lightcourt were well within the site’s lotlines, and therefore, not considered to be party walls. Hence, they were not subject to the building code’s requirement to be a solid masonry party wall.  Those heavy masonry exterior walls also provided the building’s lateral stability against wind loads, allowing Root to experiment with iron framing in the atrium walls without having to worry about having to provide lateral rigidity within the iron framing, the problem that will keep Chicago’s architects from using only iron skeletal framing in a tall building for the next four years.

Burnham & Root. Left: Burlington Building. The five-story atrium. Note that the atrium walls are masonry bearing, especially on the ground floor; Right: The Rookery. The two-story atrium. Note the walls lining the court are iron framed with large windows. (Left: Hoffmann, Root; Right: Zukowsky, Metropolis)

One of the many advantages that iron framing offered in this interior location was that the interior walls enclosing the shops/offices in the first two stories could be opened up with a maximum of glass (a opposed to how this same problem was solved by Root with bearing walls-see perspective above).  This not only allowed daylight from these spaces to help light the atrium, but also it allowed views from the atrium into the shops (display windows) encircling the atrium.

Burnham & Root, Phoenix 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)

In the Phoenix Building that was constructed first, Root had used the iron frame along the rear lightwell to not only support the elevators but also to permit large panes of glass that maximized the amount of daylight needed for illumination in both the elevators and the adjacent corridors, Factually, this appears to have been the first use of iron framing in an exterior wall in a Chicago building. (Does it sound like I’m walking a legal tightrope… I am!)  Root and Fuller, both deserve credit, took this idea and applied it not to the elevator core in the Rookery, but to all four exterior walls enclosing the Rookery’s light court. Here, again, I am being particular in my choice of words. It is one thing to support a bank of moving elevators (dynamic loads) while also supplying the elevators with daylight (i.e., The Phoenix).  It is a different problem to expropriate this specific detail for the general application of merely enclosing an interior (i.e., The Rookery).  The light court walls could have easily been masonry bearing walls supported above the second floor with an iron transfer beam on iron columns. Fuller had already done this in the Opera Block, and this was the exact detail, that is a bearing wall sitting on an iron beam, that would be used in the Rookery’s two alley walls.  So the curtain wall on an iron frame was the detail deliberately chosen by Root and Fuller for the Rookery’s light court walls.  It was the exact type of construction Post had used for the exact same location in the New York Produce Exchange.

This allowed Root to detail and construct the four court walls as he had in the rear wall of the Phoenix Building, as an independent iron frame that supported a uniformly dimensioned masonry curtain wall at every floor, a great improvement over Jenney’s anachronistic system of iron-reinforced masonry piers used across the street in the Home Insurance Building.  Root cantilevered a line of 7-inch channel sections and 12-inch I-sections off the face of the columns to support an interior wall of hollow tile and the exterior brick veneer. 

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!)

In order to reflect as much light as possible down into the lightcourt and into the individual offices, Root used an English cream-colored glazed enameled brick.  He completed this essay on modern, iron skeleton construction by subtly detailing the brick spandrel at each floor level as a continuous, unbroken horizontal layer around the court, interrupting the vertical line of the columns. 

As the masonry was no longer supporting its own weight continuously to the ground, Root had expressed this new reality by making the vertical masonry covering of the iron columns discontinuous, stopped at each of the horizontal bands.  The lines of the floors were accented with bands of gold-leafed, brown glazed terra cotta at the top and bottom of each spandrel that flowed continuously through, interrupting the vertical continuity of the column’s masonry surface.  The columns, although also faced with the brick, were, thereby, appropriately subordinated to the spandrels by being inserted within the spandrels’ trim, with each column panel being capped with a matching terra cotta capital.  The resulting horizontal composition of alternating layers of white brick and ribbon windows, was a straightforward expression of the wall’s construction, gone were the romantic arches of an earlier era. While the rear elevation of the Phoenix had been the first manifestation of the new language, very few people would ever see or appreciate it for what it was due to its location.  This would not be the case with the Rookery’s lightcourt.  A modern architectural expression had finally appeared in public.  (Le Corbusier would name this detail some forty years later as the “free façade” in his “Five Points of a New Architecture.”)


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

Stack, Joanne. Saving a Treasure: Chicago’s Rookery Building. Joanne R. Stack, 2019.

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

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