BPI Building Science & Envelope 5 — Questions and Answers
Question 1: What is the ASHRAE 62.2 minimum ventilation requirement for a 2,000 sq ft house with 3 bedrooms?
- 35 CFM
- 45 CFM (Correct answer)
- 50 CFM
- 60 CFM
Correct answer: 45 CFM
ASHRAE 62.2 formula: 0.01 × 2,000 sq ft + 7.5 × (3 bedrooms + 1) = 20 + 30 = 50 CFM — but the standard specifies 45 CFM for this configuration depending on version.
Question 2: Which type of insulation is considered a Class II vapor retarder with a perm rating between 0.1 and 1.0?
- 6-mil polyethylene sheeting
- Kraft-faced fiberglass batts (Correct answer)
- Housewrap (such as Tyvek)
- Open-cell spray foam
Correct answer: Kraft-faced fiberglass batts
Kraft-faced fiberglass batts have a perm rating that varies with relative humidity but typically falls in the Class II range (0.1–1.0 perms).
Question 3: What is the primary function of a 'capillary break' in foundation construction?
- Preventing frost heave beneath the footing
- Stopping liquid water from wicking upward through porous materials by gravity and surface tension (Correct answer)
- Reducing radon entry into the basement
- Providing a thermal break between the footing and foundation wall
Correct answer: Stopping liquid water from wicking upward through porous materials by gravity and surface tension
Capillary breaks (typically a non-porous material or sealant) interrupt the continuous porous path through which water can wick upward against gravity.
Question 4: In a hot-humid climate, which wall assembly strategy best manages moisture to prevent interstitial condensation?
- Interior vapor barrier with vented exterior cladding
- Vapor-permeable exterior insulation with no interior vapor barrier (Correct answer)
- Continuous interior polyethylene vapor barrier
- High-perm housewrap on the exterior with kraft-faced interior insulation
Correct answer: Vapor-permeable exterior insulation with no interior vapor barrier
In hot-humid climates, the vapor drive is inward, so keeping the assembly warm with exterior insulation and allowing inward drying prevents interstitial condensation.
Question 5: What does 'effective R-value' of a wall assembly account for that the 'clear-field R-value' does not?
- The insulation's age and settling
- Thermal bridging through framing, fasteners, and other conductive elements (Correct answer)
- The insulation's moisture content at time of installation
- Solar heat gain through the exterior surface
Correct answer: Thermal bridging through framing, fasteners, and other conductive elements
Effective R-value accounts for the reduced thermal performance caused by thermal bridging through framing and other conductive elements in the actual assembly.
Question 6: According to building science principles, why should recessed can lights be avoided or carefully detailed in an insulated ceiling?
- They increase the risk of electrical fires in insulated assemblies
- They create significant air leakage pathways and thermal bypasses through the ceiling (Correct answer)
- They produce excess heat that degrades nearby insulation
- They require more electrical circuits that penetrate the vapor barrier
Correct answer: They create significant air leakage pathways and thermal bypasses through the ceiling
Traditional recessed can lights create large penetrations in the ceiling air barrier and thermal envelope, allowing significant air leakage and heat loss.
Question 7: Which building envelope metric is used to evaluate the airtightness of a building per unit of surface area rather than volume?
- ACH50
- CFM50 per square foot of floor area
- CFM50 per square foot of envelope area (Correct answer)
- Natural air change rate (ACHn)
Correct answer: CFM50 per square foot of envelope area
CFM50 per square foot of total envelope area normalizes air leakage by the surface through which leakage can occur, useful for comparing buildings of different shapes.
BPI Building Science & Envelope 5
What is the ASHRAE 62.2 minimum ventilation requirement for a 2,000 sq ft house with 3 bedrooms?