Building FAR calculation question
You are working on the preliminary design of an office tower project in an urban context. The lot is 20,000 square feet. The FAR is 2.0. You want to leave 25% of the lot uncovered for a public plaza. How many stories will your building be?

Hi Valerie,
OK. So the building can be 40,000sf, which is the FAR of 2.0 x 20,000sf. The lot is 20,000sf and since they want to leave 25% of it uncovered, then we are down to 15,000sf usable lot. Since the building can be 40,000sf ÷ 15,000sf = 2.67 floors. We need to round up if we want to built out the max 40,000sf, so it's 3 floors.
This is a good ARE question. Hope this helps!
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

The floors can be SMALLER than 15,000sf, just not larger!
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

You need to calculate for the max footprint for FAR. The owner and the AHJ are not going to care about the smallest building they can build.
And there will be other height and area limitations in the building code.The ARE isn’t going to give you trick questions or play semantics like this.
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

If I were to write this question, I probably would have added a condition:
The owner wants to have the maximum square footage at a minimum construction cost. This will eliminate a lot of possible and make it a harder practice question. This is usually the case in real practice anyway.
Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

Juan,
The thirdfloor area is smaller. The areas for the 3 floors do NOT have to be the same.
Gang Chen, Author, AIA, LEED AP BD+C (GreenExamEducation.com)

The question says they want to leave 25% of the area of the site unbuilt. The footprint can only 15,000sf, so you will need 3 floors to build a 40,000sf building. In all likelihood the TOP FLOOR would probably be smaller.
You have to solve ARE questions based on the information given. If they wanted to leave more area of the site unbuilt, they would have said that. But the question clearly states that they want to leave 25% of the site uncovered, so the footprint will be 15,000sf. It doesn't say 25% OR MORE of the site. If it did, then there would be other options. But it says 25%. This is why it's so important to read the ARE question very carefully.
Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

Rebekka,
Could you have a building that the first floor is 15,000sf and the rest of the floors be 5,000sf making the building 6 stories?
1st floor = 15,000sf
2nd floor  6th floor = 5,000sf
Total = 40,000sf
If you can make the "TOP FLOOR" smaller then you can make every floor above the 1st floor smaller. I am just trying to figure our out why 3 stories. Thank you for your help.
Please sign in to leave a comment.
Comments
11 comments