Cubic or rectangular shape with more building cost?

Hello,

I looked at Ballast Practice Exam, #200 asked about building cost comparisons. In the answer explanation, it states: 1. "The higher the perimeter-to-floor area ratio, the greater the unit cost." and

2. "A cubic building costs more than a rectangular building of the same area (because a cubic building has the least amount of exterior envelope compared with a rectangular building. The contractor can also capitalize on economics of scale, the more material purchased, the better the deal)".

I get confused here, isn't that these two are conflict? Suppose a one story cubic building has 40'(W)X40'(L), with perimeter=160' ,and GFA=1600 SF. Perimeter/Floor area=0.1

Another one story rectangular building has 20'(W)X80'(L), with perimeter=200', GFA=1600 SF. Perimeter/Floor area=0.125

If per statement 1, Cubic building cost less, which is different from statement 2. Could someone help to clarify? Thanks!

Rebekka O'Melia March 29, 2021 18:15 (Edited March 29, 2021 18:17)

Hi Yuting.

I don't have access to that particular question, but I am going to say that the answer would be the smallest footprint. See this question I wrote. (The answer is C).

It would require less excavation, and less concrete. (The compact form would also be easier to heat, but that isn't mentioned as being an issue in this scenario).

Hope this helps!!

Rebekka O'Melia, B.Arch, M. Ed, Registered Architect, NCARB, Step Up ARE Prep

Yuting Song March 30, 2021 17:33

Hi, Rebekka, thanks for your illustration, that makes more sense! Very helpful!

Cubic or rectangular shape with more building cost?

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