NCARB question regarding ballast zone diagram
Hi,
Can someone explain this question to me? I don't understand how to read it what does h mean? how is the zoning done? and where can I find the resources for this question? 
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It is designed to make you think. The Roof Height minus the existing grade elevation will give you the height of the building. 1361-1321 = 40'. Which is h, so h=40. Each corner is defined as "Item 3" in terms of the height h, or 60% of the height. The "fascia" along each side of "item 3" is .6*h=.6*40=24'
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The question specifically asks about the length of the zone along the fascia, not depth. For the ARE, focus only on what's specifically being asked.
A ballast depth for each zone would accompany the diagram, in practice. The purpose of the diagram is only to explain the extent of each zone.
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Matt Dupuis, roofing God, tackled the issue of wind uplift and low-sloped roofs in a recent 40 Minutes of Competence. You can watch it here.
NCARB, if you are reading this, know that 90%+ of new roofs do not use ballast to hold them down. That kind of phased out in the 1980s. Today's membrane roofs have many of the same uplift issues, so the wind-pulls-up-the-roof-at-the-corners concept kinda still holds, but going forward, exam items probably should look at these topics through the lens of synthetic rubber membranes that are glued, mechanically fastened, held down by very cool exotic measures, etc.. The legacy matrix textbooks still include the gravel ballast content because . . . well, why would they delete good content that hasn't been completely phased out and is still on some existing buildings ... but I suspect no new construction book would give many words to gravel ballast roofing and no roofing expert would include a question on a 2023 architecture licensure exam that included gravel ballast. Please consider using subject area experts rather than volunteer licensed architects to make these questions. I can't imagine the reaction I would get if I suggested to my professor colleagues that, instead of creating their final exams themselves, they instead ask those who had completed the course in past semesters to volunteer to write the exam questions for this year's cohort.
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Matt Dupuis is a total legend. He teaches a two-day class for practicing professionals on low-sloped roofs at the University of Wisconsin. It is phenomenal. You can be a beginner or an expert and still learn. I plan on taking it again and again every few years to stay current. Thanks, Michael for the 40 Minutes of Competence link — I’ve taken the UW course and will *still* watch. He’d be a great person for NCARB to consult for all roofing questions as he’s both an academic with impeccable credentials and a practicing engineer who is among the most highly regarded experts among other professionals.
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I’ve been looking at this question and reading Brett Bowers explanation over and over again and this still doesn’t make any sense to me.
First of all, is this a plan view? The explanation from NCARB is multiplying the building height by .6 - why? .6 is being shown as a dimension in plan view, but the key says it equals height above grade. If so, .6 what? .6 feet? .6 inches? Neither makes sense. I take it from some of the explanations that it’s meant to mean 60%, but that doesn’t make much more sense. 60% high? If that’s the case, shouldn’t the question read “What is the height of the fascia above grade?”
But it doesn’t, it’s asking for the “dimension along the fascia for the ballast of corner zone 3”. What does that have to do with building height?
Am I fundamentally misreading this diagram? Can someone please help me understand?
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Nenad - Yes, this is a plan view of a roof. Regardless of the appropriateness of including a question about a ballasted membrane roofing system on a modern licensing exam, the sketch is simply showing a plan diagram of how the ballast material needs to be laid out in order to ensure the membrane remains in place. As Michael mentioned though, low sloped roof membranes are typically secured mechanically or with adhesives these days.
.6 is a unitless ratio. The required extent and depth of the ballast material is related to uplift, and therefore the height of the building above grade. That is why the ballast material layout references a ratio of the building height. Why exactly that ratio is beyond the scope of the exam.
As Christine alluded, don't get caught up in the 'why' of these exam questions. These types of questions are basically just logic puzzles that use architectural terminology. Your ability to correctly answer the logic puzzle is (theoretically) dependent on your understanding of the term and/or how it's generally used in practice.
Hope that helps.
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Certainly, let's analyze the image and the provided information to determine the dimension along the fascia for the ballast of corner zone 3.
Image Analysis:
The image depicts a diagram with various zones labeled 1, 2, and 3. Dimensions are provided in terms of "h," representing the height above grade. Corner zone 3 is specifically mentioned in the question.
Given Information:
- Existing grade elevation: 1,321.00 feet
- Roof height: 1,361.00 feet
Calculations:
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Height above grade (h): 1,361.00 feet (roof height) - 1,321.00 feet (grade elevation) = 40.00 feet
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Dimension along the fascia for corner zone 3: 0.6h = 0.6 * 40.00 feet = 24.00 feet
Therefore, the correct answer is B. 24 feet.
Explanation:
The diagram represents a ballast zone chart, likely used for determining the depth of ballast required for different roof areas. The "h" value signifies the height above grade, which is calculated as the difference between the roof height and the existing grade elevation.
In this case, the dimension along the fascia for corner zone 3 is specified as 0.6 times the height above grade (h). By calculating the height above grade and multiplying it by 0.6, we arrive at the correct answer of 24 feet.
I hope this comprehensive explanation is helpful! Let me know if you have any further questions.
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I don't understand why NCARB would consider it a professional requirement to decipher riddles, but well... This question is purposefully mixing depth and length to confuse the student. You need to calculate DEPTH h by subtracting total roof height minus grade height, which gives you 40 ft. And then you apply that number to the LENGTH of the required dimension because whoever drew this plan thought it would be funny to express distance as an equation in terms of height... So each distance that says 0.6h means that 0.6 x 40 = 24.
I'm guessing next time you submit a drawing to the AHJ for permits you can definitely apply this NCARB-approved terminology and you can submit for example, window height in terms of slab depth, so your windows can be 5s where s="depth of slab" and that way AHJ can definitely have some fun solving the mathematical/architectural riddle? (Dear fellow confused architecture students, this last bit is a sarcastic joke / analogy that hopefully helps the reader understand both NCARBs question and my critique of it. Please refrain from expressing dimensions in terms of arbitrarily selected equations.)
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