The building’s exterior form we have discussed at some length under “commodity.” The form of the major portion or body of the skyscraper was determined from an intense study of what was the best configuration for the typical office floor plan, based on maximizing rentable floor area and how it was to be daylighted. Once a plan had been finalized, it simply was extruded vertically for either as many floors the owner wanted or to the maximum height allowed if a building or zoning code had been enacted at the time of design. The body of the building, thus configured, would be placed on a base that sat on the ground. As opposed to the body that at times could break away from the plane of the lot line whenever a lightcourt came into play, the base of these skyscrapers always held to the lot lines, so as to maximize the amount of rentable floor area in this high-rent zone. This also applied to the basement, where the need for space continued to grow as buildings became more mechanized and the basement was a logical location for the equipment. Banks, public offices of major companies, and stores were the standard tenants not only for the ground floor, but also in many cases, for the second floor (typically referred to as the entresol or mezzanine) as during this time one flight of stairs was not viewed as an impediment.
Tradition dictated that the building’s elevation be symmetric about a central axis (this assumes that the lot was big enough to accommodate such a plan that was not always the case). This was reinforced by the introduction of the elevator that wanted to be centrally located to minimize walking distances to either end of the corridors. This typically resulted in the entrance being placed in the middle of the elevation. Sometimes the main entrance was marked simply by a door placed in the center window on the ground floor facade, or an architect might insert a triumphal arched entry at this point.
A third alternative for the entrance was the addition of a portico or architectural canopy that projected in front of the body of the building.
The center of the building could also be marked by either by the addition of a pediment at the building’s cornice or the slight projection/recession (see top image) of the central portion of the wall relative to the flanking ends of the wall.
One of the major design issues that divided the European styles that were used in the early skyscrapers into two camps was the design of the roof. Was it necessary to see the roof from the ground, or was the building to be a simple box with four walls? The Italian palazzo and the German Rundbogenstil styles were primarily a “wall” architecture, with no visible roof so the vertical plane of the wall was the primary visual element to be seen, and therefore, designed. The British Victorian Gothic/Queen Anne and the French Second Empire styles celebrated the roof as the culmination of the building’s massing; the Second Empire style requiring its particular type of roof, the Mansard, to be incorporated into the design, even if it was merely a fake sloping wall of the top floor. Buildings with a roof compounded the design theory of the tripartite elevation (a top, a middle, and a base). The European Classical tradition dictated that the elevation of a building should be treated like that of a classical column, that is, it should have a base or bottom, a shaft or middle, and a capital or top. With regards to the tradition of the tripartite elevation, was the roof to be incorporated with any portion of the top floor as the “cap” or could a roof be added to a wall that was already designed into three parts, thereby adding a fourth element to the elevation?
4.4. THE ELEVATIONS: OPENINGS IN THE WALL
It is this next design issue, the articulation of the building’s exterior wall, elevation, or façade that would be the most challenging in the evolution of the skyscraper. As there were no precedents from the past to inform the designer facing the problem of a ten-story skyscraper, invention would necessarily have to play a significant role in the design of a skyscraper’s exterior elevation. The problem an architect faced is simply put: how to detail holes (windows) in a wall. The artistic challenge was the “how.”
Historically (traditionally), making an opening in a stone or masonry wall was controlled by the manner in which an architect chose to cover the opening in the wall. If using stone, as long as the stone available was long enough to span the opening, a horizontal beam or lintel could top the opening that generated a horizontal or flat-headed opening. That is, as long as the stone’s tension strength was not exceeded, for the stone was a beam that would deflect in the center due to gravity. This deflection caused the bottom of the beam to elongate or stretch, generating considerable tension, that eventually could exceed the stone’s tension strength. If this happened, the stone would crack and collapse into the opening below. Wood has a much larger capacity to resist tension, and therefore, can span farther than stone, but wood is not always resistant to fire, and therefore, could not be used. In order to span greater distances than the limit of a stone beam with a fireproof material, the arch was developed (this happened long before the invention of cast iron).
The arch is a structural element that due to its shape, remains in pure compression. Stone has a very high compression strength, therefore, a stone arch has no real limit as to how far it could span, as the Pantheon in Rome (148′) reveals. There are two inherent differences an architect had to deal with when he used an arch as opposed to a lintel to cover an opening or window. First, the shape of the head of the window could be curved in any number of ways (shallow segment of an arch to a pointed arch), including a flat-arch. Second, an arch generates thrust, a horizontal force that tends to push the supports of the arch apart from one another. A lintel does not develop any thrust, so in a wall that uses beams, the corner columns can be the same size as the interior columns. Not so with a wall that uses arches. While the thrust from adjacent arches offset each other, the column at each corner does not have an adjacent arch, and therefore, must be larger than the other columns to resist the thrust of its arch. One could make a visual analogy with a picture frame. A wall that uses arches to span its windows requires heavier corner columns/piers that create a frame on both ends of the wall or facade.
To support the gravity load of a building, architects and builders had a choice of one of two systems: either vertical walls (plane/surface) or vertical columns (lines). Hence, the exterior of an early multistory building would consist of either a repetitive stacking of columns and beams or a wall plane punctured with window openings, be they flat- or arch-headed. The column/beam option was initially the more expensive option because it was harder and more expensive to construct, so most builders turned first to the wall with openings to support the multi-storied building.
(If you have any questions or suggestions, please feel free to eMail me at: firstname.lastname@example.org)