From Andrés Duany’s “Classic Urbanism“:
From time to time there appears a concept of exceptional longevity. In architecture, the pre-eminent instance is the Vitruvian triad of Comoditas, Utilitas, e Venustas. This Roman epigram was propelled into immortality by Lord Burlington’s felicitous translation as Commodity, Firmness and Delight.
It has thus passed down the centuries and remains authoritative, even if not always applied in practice; Commodity: That a building must accommodate its program; Firmness: That it must stand up to the natural elements, among them gravity; Delight: that it must be satisfying to the eye, is with the aberrant exception of the tiny, current avant garde, the ideal of architecture. …
Let me propose the urban triad of Function, Disposition and Configuration as categories that would both describe and “test” the urban performance of a building.
Function describes the use to which the building lends itself, towards the ideal of mixed-use. In urbanism the range of function a first cut may include: exclusively residential, primarily residential, primarily commercial or exclusively commercial. The middle two being the best in urban performance although the extremes have justification in the urban to rural transect. An elaboration should probably differentiate the function at the all-important sidewalk level from the function above.
Disposition describes the location of the building on its lot or site. This may range from a building placed across the frontage of its lot, creating a most urban condition to the rural condition of the building freestanding in the center of its site. Perhaps the easiest way to categorize the disposition of the building is by describing it by its yards: The rearyard building has the building along the frontage, the courtyard building internalizes the space and is just as urban, the sideyard building is the zero-lot line or “Charleston single house” and the edgeyard building is a freestanding object closest to the rural edge of the transect.
The third component of the urban triad is Configuration. This describes the massing, height of a building and, for those who believe that harmony is a tool of urbanism, the architectural syntax and constructional tectonic. It can be argued that the surface of a building is a tool of urbanism no less than its form. Silence of expression is required to achieve the “wall” that defines public space, and that reserves the exalted configuration to differentiate the public building. Harmony in the architectural language is the secret of mixed-use. People seem not to mind variation of function as long as the container looks similar. It is certainly a concern of urbanism.