The most common form of architectural problem involves land area that is given, but in some cases the land area is unknown and the gross building area objective has been defined. If I were to guess, this condition is encountered far less frequently, but there is an entire series of forecast models devoted to predicting land area solutions when gross building area GBA is known and height is an option. They are included in software entitled, Development Capacity Evaluation, v.2 that is attached to a book/ manual entitled, Land Development Calculations, 2.e, McGraw-Hill, 2009. The forecast model CG1B is included as an example and labeled Figure 1. The “C” stands for all non-residential land uses. The composite “G1” indicates the design category, which in this case is grade parking around, but not under, the building. The “B” indicates that the gross building area is given.
The design specification template in Fig 1 is used to enter given information. Data entry locations are indicated with boxes containing bold and blue typeface. The values entered can be changed at will to test an unlimited number of design options. The project open space value (S) and the parking values (s) and (a) produce the most noticeable forecast changes when altered.
The planning forecast panel below the template also contains a data entry column that permits floor options FLR to be tested beyond those listed. The number of floors contemplated is a design variable that also produces significant changes in the buildable land area needed.
Figure 1: Forecast Model CG1B
The term “buildable land area” BLA and BAC were not casual references; and the term “gross buildable land area” GBLA in this context includes right-of-way dedication and future expansion area estimates. The total land area TLA that must be purchased can be significantly different from the gross buildable land area needed GBLA. Such things as ponds, ravines, historic reserves, extreme topography and unstable soil must be subtracted from the TLA to define the GBLA remaining for the purposes anticipated. These areas cannot be predicted by forecast models, but must be included in any final analysis of the potential site location and area needed.
Finally, my essay, “Taking the Pulse of Architecture”, suggested the following equation to define architectural intensity:
I = GBA / (S*BLA)
In this equation, “I” is intensity. “GBA” is in sq. ft. “BLA” is in sq. ft., and “S” is project open space expressed as a percentage of the BLA provided.
BLA does not include rights-of-way and future expansion areas.
Intensity statistics INT are reported in the right hand column of Fig 1.
The line drawn under the five story statistics in the planning forecast panel indicates that anything greater than five stories produces a negligible increase in GBA for the G1 design premise under consideration. I have explained these relationships in “Replacing Density” and “The Limits of Shelter Capacity”.
The entire list of forecast models available can be found on pages 4-6 of the book mentioned above and can be previewed on Amazon.com. The intensity equation mentioned above is an improvement, however, and this version is not calculated in the forecast models mentioned.