Understanding a Building Footprint

I recently wrote an essay entitled "The Future of Cities" that introduced the G1 Building Design Category and its master equation for gross building area that I called (G1.L1):

GBA = CORE * af / (a + (fs))

KEY:

a –              gross building area square feet permitted per parking space provided

CORE –     buildable land area available for building and parking cover in square feet

f –               floor quantity

GBA –       gross building area potential in square feet

s –              gross parking lot area provided per parking space provided in square feet

The essay explained that when (GBA) is divided by (f), the result is gross building cover area (BCA), also known as building footprint or floor plan. It also noted that (BCA) was equal to 0.1111 of the core land area, but it did not mention the obvious. Eleven percent (0.1111) of a core area is a very small percentage when you consider that core area is the area that remains for building and parking cover after a number of related land areas are subtracted from the gross land area available. It is a surprising statistic, but the formula for maximum potential building floor plan area is one that can give design leadership a simple site planning tool. If maximum floor plan area can be predicted, design results can be easily measured to ensure compliance with leadership intent.

The formula for building cover can be easily derived from the G1.L1 master equation noted above:

Given: BCA = GBA / f

Find: BCA when CORE area is equal to 1.0 in Equation G1.L1:

GBA = af / (a + (fs))                          Equation G1.L1 coefficient

BCA = (af) / (a + (fs)) / f                  Substitute GBA in BCA

BCA = af / ((af) + (f²s))                     Reduce BCA

BCA = a / (a + (fs))                          Reduce BCA to coefficient equation

BCA = CORE * a / (a + (fs))            Reintroduce CORE to form Equation G1.L1.BCA

Remember that Equation G1.L1.BCA only applies to the G1 Building Design Category. When core area is defined by subtraction of estimated land area quantities in a G1 design specification template, the maximum footprint area (BCA) can be found when values are assigned to (a), (f), and (s) in Equation G1.L1.BCA. (The coefficient equation can be useful when presenting options. A sample G1 design specification template explaining the subtraction the leads to core area definition can be found in my essay, “The Future of Cities”. A sample of coefficient evaluation can be found in Table 2 of this essay.)

If you use Equation G1.L1.BCA you will find what every building designer has intuitively observed since automobiles became a G1 site planning topic; but if you are like me, the small percentages will still be a surprise.