CMA Moisture & Building Science Flashcards

What is the primary driving force that allows moisture to move through building materials by capillary action?

Answer: Surface tension in pore spaces

Capillary action is driven by surface tension within small pores, pulling liquid water through materials without pressure.

Which relative humidity (RH) range is generally considered the threshold above which mold growth is likely to begin on building materials?

Answer: Above 60% RH

Sustained relative humidity above 60% at material surfaces creates conditions favorable for mold colonization.

In building science, what does the term 'dew point' refer to?

Answer: The temperature at which condensation forms on a surface

Dew point is the temperature to which air must be cooled for water vapor to condense into liquid at a given moisture content.

Which type of vapor retarder is classified as Class I under the International Residential Code (IRC)?

Answer: Polyethylene sheeting (6 mil)

Class I vapor retarders have a permeance of 0.1 perm or less, which includes materials like polyethylene sheeting.

What is the primary cause of interstitial condensation in wall assemblies?

Answer: Warm moist air meeting a cold surface within the wall cavity

Interstitial condensation occurs when warm, humid interior air migrates into a wall and contacts a surface below the dew point.

Which building material typically has the highest moisture sorption capacity, making it a significant mold substrate risk?

Answer: Paper-faced gypsum drywall

The paper facing on gypsum drywall is cellulose-based, which readily absorbs moisture and provides nutrients for mold.