Net Square Footage Question  Walking the ARE practice question
Can someone please help me understand this PA practice question from Erik Walker's exam?:
10. A new retail center is in the works on a 100’ x 75’ site with a 15foot setback on each side. The site according to the local zoning code has a FAR of 3.0. The owner of the retail center has asked that the building has an estimated building efficiency of 75%. What is the largest net floor area that the developer could build on this site? (Fill in the blank, round to the nearest foot)
Here is the answer:
10.) For this question we need to calculate the largest net square footage based on the given constraints of a 100foot x 75foot site with 15foot setbacks on each side and a FloorAreaRatio (FAR) of 3.0. Here is the math for that: (Site Area) (FAR) = Total S.F. (100’ x 75’) (3.0) = 22.500 S.F. In this question, the property setbacks literally mean nothing to us when calculating the total floor area ratio of the building, all that is going to do is drive how many stories we will be required to construct on order to reach that 22,500 Gross S.F. number. However, this question is asking for largest net square footage and it gives us a 75% efficiency rate. (which is typical for a retail center) Since we know our gross square footage and are given the efficiency rate, we can find the net square footage. Here is the math for that: (22,500 Gross S.F.) (0.75) = 16,875 Net S.F. The correct answer is 16,875 net S.F.
Why are the 15' property setbacks are not included in the equation? My first thought was that the gross square footage would be (45' x 70') (3.0)=9,450
Thanks for the help!

Maximum allowable building area requires to use the lot area x FAR which is 3.0 as Eric explained setbacks would be required to get how much of this area you will distribute in a certain number of stories. In this case the question asks for net area reasons why he multiple lot area x 0.75 which is the building efficiency ratio. Hope this help!

I don't like the 'estimated building efficiency' part of this question. The 75% would be the LEAST efficient and there's no reason why the FAR couldn't or wouldn't be at 100%. Efficiency usually refers to energy usage. It's actually less efficient to build a smaller building with less stories. I think he meant to say that the client wants to keep the building under the FAR.
I came up with 22,500sf at FAR 3.0. This would be a 7 story building with 3,150 sf per flr. At 75% the building would be 5 stories instead.
Hope this helps!
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, Step UP ARE 5.0 Courses
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