CMA CMA Moisture & Building Science 1 — Questions and Answers
Question 1: What is the primary driving force that allows moisture to move through building materials by capillary action?
- Surface tension in pore spaces (Correct answer)
- Vapor pressure differential
- Thermal gradient
- Wind-driven rain pressure
Correct answer: Surface tension in pore spaces
Capillary action is driven by surface tension within small pores, pulling liquid water through materials without pressure.
Question 2: Which relative humidity (RH) range is generally considered the threshold above which mold growth is likely to begin on building materials?
- Above 50% RH
- Above 60% RH (Correct answer)
- Above 70% RH
- Above 80% RH
Correct answer: Above 60% RH
Sustained relative humidity above 60% at material surfaces creates conditions favorable for mold colonization.
Question 3: In building science, what does the term 'dew point' refer to?
- The temperature at which condensation forms on a surface (Correct answer)
- The lowest outdoor temperature recorded in a day
- The moisture content of building materials
- The point at which rain penetrates a wall assembly
Correct 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.
Question 4: Which type of vapor retarder is classified as Class I under the International Residential Code (IRC)?
- Kraft-faced batts
- Polyethylene sheeting (6 mil) (Correct answer)
- Latex paint
- House wrap
Correct answer: Polyethylene sheeting (6 mil)
Class I vapor retarders have a permeance of 0.1 perm or less, which includes materials like polyethylene sheeting.
Question 5: What is the primary cause of interstitial condensation in wall assemblies?
- Exterior rain wetting the cladding
- Warm moist air meeting a cold surface within the wall cavity (Correct answer)
- Plumbing leaks inside the wall
- Foundation moisture wicking upward
Correct 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.
Question 6: Which building material typically has the highest moisture sorption capacity, making it a significant mold substrate risk?
- Concrete block
- Ceramic tile
- Paper-faced gypsum drywall (Correct answer)
- Glass fiber insulation
Correct answer: Paper-faced gypsum drywall
The paper facing on gypsum drywall is cellulose-based, which readily absorbs moisture and provides nutrients for mold.
CMA CMA Moisture & Building Science 1
What is the primary driving force that allows moisture to move through building materials by capillary action?