Is this another wrong question (example 14.2) from Ballast 5.0 Review Manual..?
Please help me with this cause I believe the answer of this question should be 0.4, not 0.33. Because the W is 24 instead of 20. According to IBC2015 506.3.2 W is the measured to the closest interior lot line (or the building face) that is minimum 20 feet. The question only gives us one distance which is 24 feet and as I understand it expects us to assume that W is not varying along the perimeter. So we don't need to apply Equation 54 of IBC2015 to find the W value.
So the answer should be:
If= [(180/240) 0.25] x 24/30 = 0.4..????
Thanks and Happy Thanksgiving!!

Elif,
in my opinion...
IBC section 506.3.2 seems to say that the value of "W" is 20 (as long as the actual distance is greater than or equal to 20 feet, but less than 30 feet). Remember, distances of over 30 ft. are handled in this way.
If that is the case, Ballast's answer of 0.3 (0.33) would be accurate.
However, according to the IBC 2015 code commentary this interpretation is inaccurate. The value of W is 24 feet based on the weighted average method found in section 506.3.2. Therefore, (((180 ft /240 ft)  0.25)* 24 ft.) / 30 = 0.4 or answer D.
Ballast's interpretation of code would seem to be inaccurate in this case (although you could make the argument to some code officials that this interpretation is acceptable  and win).
As always though, check up on this yourself.
Good catch!

I came across this question and also got 0.4. The way that Ballast describes “W” is “the width of the public way or open space, which must be at least 20 ft; W may not be taken as greater than 30 ft, even if the actual width is greater.”
Based on this, it means that W is greater than, or equal to, 20 ft and less than it equal to 30 ft. That said, the equation should have W at 24 feet; giving you an area factor increase of 0.4 (40%).
I take the PPD exam in a few days so I guess I’ll see what happens haha.
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