NCARB question regarding ballast zone diagram

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    Dennis Bro

    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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    Brett Bowers

    Blane, the question is asking about the length of the 'leg' of zone 3, not the depth/height of the ballast.

    According to the diagram, the width of ballast zones 1 and 2 would also be 24 feet, with zone 1' making up the remainder of the roof area.

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    Brett Bowers (Edited )

    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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    Kara Zhang

    what is the point of the question? why do they make such a question?

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    Christine Williamson Cronin

    I hear you, Kara. There were a lot of these types of questions in PPD, PDD, and PA, and they’re basically just logic questions that require you to understand some architectural terminology to solve a simple problem. They could have just as easily asked what “ballast” is.

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    Michael Ermann

    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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    Christine Williamson Cronin

    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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    Nenad Videnovic

    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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    Brett Bowers

    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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