NCARB practice Exam Explanation
Hi all,
I was hoping to get a better explanation on the answer from NCARB practice exam. What confused me was:
1) Why did they use 20' side setback but not 10' or 15'
2) My understanding is FAR = Building Area/Lot Area. Why did they not use the lot area in this problem
Thank you in advance for your help.

Yes, I think NCARB's answer here is 100% wrong. You don't use the setback to calculate the FAR. The FAR is calculated using the entire site area. Then you try to get as many sf to fit inside the setback, at the max height allowed by zoning. This question is complicated the fact that it's saying the setback change for different heights. What does the zoning say is the max height for residential in this zoning?
The tallest building (even with the increased setbacks) will be biggest sf.
I'd take up this issue with NCARB. Hope this helps!
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses

The NCARB question is not wrong  you have to carefully read the problem (which is my biggest problem, I am always looking to skim).
The problem states: "the Owner wants to build each story to the extent of the required setbacks"  this right here tells you exactly what you need to know. They are GIVING you the FAR (4.0) to calculate how many stories you can build they are not asking you to calculate the FAR. So in this case, you need all the information the problem presents.
Your lot is (190x60) = 11,400SF  with an FAR of 4.0, your maximum buildable [or gross floor] area is 45,600SF for the building. But, the problem states the Owner wants to maximize the building to the setbacks. So you have to calculate each scenario with the setbacks and find which of the scenarios yields the greatest buildable area without exceeding 45,600SF.If your building is 1story, you lose 20ft to side setbacks  that means your floor plate is (155x40)=6,200SF. Since you are only allowed 1story in this scenario, no point is further calculating. This answer is listed, but let's follow through the other scenarios to see if there is a greater (maximized) choice.
If your building is 2stories, you lose 30ft to side setbacks  that means your floor plate(s) are (155x30)=4,650SF. Now x2stories, you get 9,300SF. The answer is not listed, so let's move on.
If you building is 35 stories, you lose 40ft to side setbacks  that means your floor plate(s) are (155x20)=3,100SF. Now x3stories, you get 9,300SF (same as above scenario). But in this scenario/setbacks, you are allowed to build up to 5 stories. At 4stories, (3,100x4)=12,400SF. At 5stories, (3,100x5)=15,500SF. I suspect this would actually be the right answer, but there could be other factors at play like building heights and it's not listed.
The answer is (c) 12,400SF. 
This is a poorly worded problem, but I do not think it is incorrect as Lauren mentioned. However, the statement "the Owner wants to build each story to the extent of the required setbacks" is really just telling us that they want to use the entire buildable area on the site.
The tricky part on this question is where is says "Based on the buildable land area, the floor area ratio for the property is 4.0." This tells us to calculate FAR based on the buildable area, not the lot area, as would typically be done.
So, after you find your buildable area for a 4 story building ((1902510)x(602020)=3,100sf), then you multiply this area times 4 stories (3,100x4=12,400sf).
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