NCARB PDD Practice Exam Question - Insulation Values
An architect is reviewing insulation values for a new two-story office building. The building is designed with an aluminum standing seam roof with insulation entirely above the structural roof deck, an exterior brick veneer and metal stud back-up wall assembly, and concrete slab on grade with concrete foundations. Insulation values are as follows:
- Fiberglass batts: R3.5 per inch
- Rock-wool blankets: R3 per inch
- Polystyrene rigid: R4.5 per inch
- Polyisocyanurate rigid: R8 per inch
Which one of the following exterior assemblies complies with the requirements listed in the table above?
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Standing seam metal roof with 4 inches of polyisocyanurate insulation, 1 inch of polystyrene rigid insulation in the brick veneer cavity, and 5 inches of fiberglass batts in the metal studs.
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Standing seam metal roof with 3 inches of polyisocyanurate insulation, 2 inches of polystyrene rigid insulation in the brick veneer cavity, and 5 inches of fiberglass batts in the metal studs.
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Standing seam metal roof with 4 inches of polyisocyanurate insulation, 1.5 inches of polystyrene rigid insulation in the brick veneer cavity, and 4.5 inches of rock-wool blankets in the metal studs.
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Did my insulation calcs and narrowed down the three choices to knowing that Choice 1 and 3 are viable. I don't understand why Choice 1 is incorrect. The explanation doesn't talk about the incorrect answers. Please help??
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Hi Amber,
Choice 1 is incorrect because the 1" of polystyrene rigid in the cavity is not enough to meet the code, which says that R-5 c.i. (continuous insul) is needed in the metal walls of a commercial building. 1" at R4.5 = R4.5.
Choice 3 is the correct one!
Hope this helps!
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
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You're welcome! And congrats on passing Amber, that's great!! You're almost done!
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
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I'm confused by this question as well.
The chart requires an R-value for 'Mass' walls (I am assuming this is the brick maybe I am wrong) of R7.6.
I had been calculating the 1.5 inches of polystyrene rigid as insulation for that wall portion, which is 6.75 and less than the mass wall in the chart requires.
Or is it that the brick is ignored and the 1.5 inches of polystyrene rigid is just extra above and beyond the steel frame wall with batts?
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Brick veneer is not a mass wall. It’s a veneer. If it were 2-3 courses of brick or solid concrete, then that’s a mass wall.
Rebekka O'Melia, Registered Architect, NCARB, B. Arch, M. Ed, Step UP, Step UP ARE 5.0 Courses
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lindamejia
The goal of this question is to utilize the code table for required insulation values and the information given in the scenario to tabulate the proposed assemblies and select the compliant one.
The question tells us that the roof being used has insulation entirely above the deck for an office (nonresidential) application. The minimum R-value for this assembly is R-25 continuous insulation. The walls are steel-framed with a brick veneer, which requires R-13 and R-5 continuous insulation.
The 3 options feature polyiso (R8/inch), polystyrene (R4.5/inch), fiberglass batts (R3.5/inch), and rock-wool (R3/inch) as the insulators in the assembly. Using these numbers, we have 4” polyiso (R32 CI) and 3” polyiso (R24 CI) for the proposed roof assemblies, which eliminates option 2 that does not comply with the requirements in the table (R25 CI).
Moving to the continuous rigid insulation for the remaining two options, we have 1” (R4.5 CI) and 1.5” (R6.75 CI), which eliminates the first option due to the table requirement (R5 CI). Finally, the 4.5" rock wool (R13.5) is compliant with the required minimum R-value for steel-framed walls above grade, making option 3 the correct option.
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