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NCARB PDD Exam - Topic 3 Question 14 Discussion

In winter conditions, when the outdoor air is below freezing and the indoor humidity is maintained at 40 percent relative humidity for 24 hours a day, ice forms on the exterior surface of the stone facing.Which of the following elements is missing from the building wall section?
A) Vapor barrier
B) Wall insulation
C) Air space
D) Rain screen

NCARB PDD Exam - Topic 3 Question 14 Discussion

Actual exam question for NCARB's PDD exam
Question #: 14
Topic #: 3
[All PDD Questions]

In winter conditions, when the outdoor air is below freezing and the indoor humidity is maintained at 40 percent relative humidity for 24 hours a day, ice forms on the exterior surface of the stone facing.

Which of the following elements is missing from the building wall section?

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Suggested Answer: A

With outdoor below freezing and indoor RH ~40% continuously, interior vapor will migrate outward. If a proper interior-side vapor barrier/retarder is missing, moisture moves through the wall and can condense and freeze at the cold exterior stone, forming visible ice. Insulation, air spaces, or rain screens help heat/moisture management, but the symptom (ice due to vapor diffusion) points specifically to the lack of an interior vapor barrier in a cold-climate assembly.

PDD references: Moisture control & vapor retarder strategy in cold climates; condensation diagnostics (ASHRAE Fundamentals; ARE 5.0 PDD---Envelope moisture control).


by Eve at May 14, 2026, 07:51 PM

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Nadine
2 hours ago
Definitely a vapor barrier issue.
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Kimberlie
5 days ago
I’m leaning towards the rain screen option, but I’m not entirely confident. I need to think about how it relates to moisture management.
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Mindy
10 days ago
Could it be the air space? I feel like that could help with ventilation and reduce ice formation.
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Vallie
16 days ago
I remember a similar question about insulation and how it affects moisture levels, but I'm not sure if that's the main issue here.
upvoted 0 times
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Malcolm
2 months ago
I think it might be the vapor barrier since that could prevent moisture from getting into the wall.
upvoted 0 times
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