BPI Building Science & Envelope 3 — Questions and Answers
Question 1: A homeowner reports that their attic insulation was installed directly over soffit vents. What is the PRIMARY concern with this installation?
- Reduced fire resistance
- Blocked ventilation causing moisture and thermal problems (Correct answer)
- Increased risk of pest infiltration
- Accelerated insulation degradation
Correct answer: Blocked ventilation causing moisture and thermal problems
Blocking soffit vents prevents attic ventilation, which can lead to moisture accumulation, ice dams, and increased cooling loads.
Question 2: What does the term 'hygric buffering' describe in building science?
- The use of vapor barriers to block moisture movement
- A material's ability to absorb and release moisture, moderating humidity swings (Correct answer)
- Mechanical dehumidification of building cavities
- The drainage capacity of a wall assembly
Correct answer: A material's ability to absorb and release moisture, moderating humidity swings
Hygric buffering refers to a material's capacity to temporarily store moisture and release it slowly, stabilizing indoor relative humidity.
Question 3: What is 'interstitial condensation' in a building assembly?
- Condensation on interior window surfaces
- Condensation forming within the wall, floor, or roof assembly between layers (Correct answer)
- Condensation in HVAC ductwork
- Surface condensation on exterior cladding
Correct answer: Condensation forming within the wall, floor, or roof assembly between layers
Interstitial condensation occurs when warm, moist air reaches a surface within a building assembly that is at or below the dew point temperature.
Question 4: According to BPI standards, what is the recommended maximum relative humidity for conditioned living spaces during winter to prevent moisture problems?
- 30%
- 50% (Correct answer)
- 60%
- 70%
Correct answer: 50%
BPI and ASHRAE 160 recommend maintaining indoor relative humidity below 50% to reduce the risk of moisture damage and mold growth.
Question 5: A blower door test measures a house at 1,800 CFM50. The house has 2,000 square feet of conditioned floor area. What is the air leakage rate in CFM50 per square foot?
- 0.45
- 0.90 (Correct answer)
- 1.11
- 0.60
Correct answer: 0.90
1,800 CFM50 ÷ 2,000 sq ft = 0.90 CFM50/sq ft, which is a common metric for normalized air leakage.
Question 6: What is the primary risk of installing a perfectly impermeable vapor barrier on BOTH the interior AND exterior of a wall assembly?
- Structural failure due to pressure buildup
- Moisture becomes trapped with no drying potential in either direction (Correct answer)
- Excessive heat gain in summer
- Reduction in the wall's fire rating
Correct answer: Moisture becomes trapped with no drying potential in either direction
A double vapor barrier creates a 'moisture trap' where any moisture that enters the assembly cannot dry to either side, leading to rot and mold.
Question 7: Which type of window frame material has the lowest thermal conductivity and best thermal performance?
- Aluminum
- Steel
- Fiberglass or wood (Correct answer)
- Vinyl with no internal insulation
Correct answer: Fiberglass or wood
Fiberglass and wood frames have much lower thermal conductivity than metals, reducing heat transfer and condensation potential at window frames.
BPI Building Science & Envelope 3
A homeowner reports that their attic insulation was installed directly over soffit vents.
What is the PRIMARY concern with this installation?