Building FAR Calculation question

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Shanglin Li

May 27, 2021 16:03

Hi guys,

When we have the lot size given for 100' x100' and a 10' set back on all sides.

The FAR is 2. What is the buildable building square footage? 

Do we use gross lot area 10,000sf multiply 2 or buildable lot area 6,400sf multiply 2? 

Thanks,

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  Gang Chen May 28, 2021 15:23

  In all of my projects, I always use gross lot area ( 10,000sf  in this case) and never had any problems. 

  Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

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  Hannah Hobbs May 28, 2021 20:13

  FAR is based off lot size, so 10k SF in this case.

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  Michelle Lowrance May 29, 2021 02:56

  FAR used to always confuse me, but after finally understanding it, it is based off of gross lot area (think of it in the sense that the floor/area ratio has nothing to do with the setbacks).  So it's 10,000sf X 2 = 20,000 sf buildable building sf. 

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  Gang Chen May 29, 2021 05:04

  NCARB wants you to really know some very basic concept and master them. How do they find out? One way to do it is to give you some extra information in the question to distract you to see if you really master the concept.

  This is a good example, FAR’s definition is very straight forward, but this question give you some extra information: “10' set back on all sides.” This information is NOT necessary to solve the problem If you did not master the concept, and you are NOT sure about yourself, you will start to overthink the problem and start to doubt yourself, and NCARB will get you.

  One way to overcome this problem is to study as hard as you can to master the concepts. However, in the real exam, if you start to have doubts, ALWAYS go with your first choice and your instinct.

  Gang Chen, Author, Architect, LEED AP BD+C (GreenExamEducation.com)

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  Shanglin Li May 29, 2021 06:06

  Thank you Gang Chen, this was really confused me because I've recently watched a Pluralsight PPD video and from the video, it specifically stated it should take the building set back into account. But from Ballast practice questions it just uses the gross lot area. I think it makes more sense to just use the gross lot area.

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  Gustavo Diez-Presilla June 01, 2021 14:27

  You use setback for coming from the FAR find out the number of stories

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  Shanglin Li June 01, 2021 23:21

  So for similar questions like calculating the building frontage coverage question, it also applies to the gross lot size, not with the setbacks?

  i.e. 

  The front lot is 100' with a setback of 10', frontage coverage is 90%.

  the building frontage should be 90', not 81'. Correct?

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  Gang Chen June 02, 2021 15:26

  Yes, the building frontage should be 90', not 81'.

  Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

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  Gang Chen June 03, 2021 15:46

  On a related note:

  Sometimes the city or other governing agencies will request the developer/owner to dedicate a portion of the land, for example, one of the project that I am working has a 10' dedication to the city for future street purpose. These kinds of dedication should be complete deducted from all above calculations.

  Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

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