Which of the following best describes the three moisture issues consultants must distinguish?

• A. Leaks, condensation, and frost risk
• B. Condensation, vapor drive, and moisture migration
• C. Leaks, condensation, and vapor drive
• D. Leaks and vapor drive only

Answer: (C)

Moisture performance in building envelopes is governed by three distinct pathways that consultants must identify to diagnose problems and plan remediation. First, leaks are direct liquid water intrusions through openings, penetrations, or defective joints—things you can see or trace to a physical flaw in the enclosure. Second, condensation happens when moist indoor air contacts a surface cooled below its dew point, causing water to condense on that surface and potentially lead to dampness and mold. Third, vapor drive is the movement of water vapor through materials driven by differences in vapor pressure; moisture can migrate through assemblies even without any visible leaks, bringing moisture to colder zones where it may condense or cause hidden damage. Distinguishing these helps tailor fixes: seal and flash leaks, control interior humidity and surface temperatures to prevent condensation, and manage material permeability or add appropriate vapor retarders to limit vapor drive. Frost risk can accompany condensation under freezing conditions, but it isn’t treated as its own separate moisture pathway.