BPI Building Envelope 4 — Questions and Answers
Question 1: What does a window's U-factor measure?
- Solar heat gain through the glazing
- The rate of non-solar heat transfer through the window assembly (Correct answer)
- Resistance to condensation on the interior surface
- Visible light transmittance through the glass
Correct answer: The rate of non-solar heat transfer through the window assembly
U-factor measures the rate of heat transfer (conduction, convection, and radiation) through a window assembly; lower values indicate better insulating performance.
Question 2: In BPI's building-as-a-system approach, which interaction is most likely to cause CO spillage from a water heater?
- Installing new attic insulation only
- Air sealing the house without addressing combustion air supply for natural-draft appliances (Correct answer)
- Replacing single-pane windows with double-pane
- Adding a whole-house ventilation fan that is interlocked with the furnace
Correct answer: Air sealing the house without addressing combustion air supply for natural-draft appliances
Tightening the envelope without ensuring adequate combustion air can depressurize the space, causing natural-draft appliances to spill CO into the living area.
Question 3: Which insulation material has the highest R-value per inch among common residential insulation options?
- Fiberglass batt (R-3.2/inch)
- Mineral wool batt (R-3.7/inch)
- Closed-cell spray foam (R-6.5/inch) (Correct answer)
- Cellulose dense-pack (R-3.7/inch)
Correct answer: Closed-cell spray foam (R-6.5/inch)
Closed-cell spray polyurethane foam provides approximately R-6 to R-7 per inch, the highest of common residential insulation products.
Question 4: What is 'effective R-value' as opposed to 'nominal R-value' of a wall assembly?
- R-value measured at extreme cold temperatures
- The actual whole-assembly thermal resistance accounting for framing members and thermal bridges (Correct answer)
- R-value of insulation before installation compression
- R-value certified by a third-party laboratory
Correct answer: The actual whole-assembly thermal resistance accounting for framing members and thermal bridges
Effective R-value accounts for heat flow through studs and other thermal bridges in the real assembly, which is typically lower than the insulation's nominal R-value alone.
Question 5: When performing a blower door test, at what pressure differential is the standard CFM measurement taken?
- 25 Pascals
- 50 Pascals (Correct answer)
- 75 Pascals
- 100 Pascals
Correct answer: 50 Pascals
BPI and ASHRAE standard blower door measurements are taken at 50 Pascals (CFM50), providing a reproducible baseline for airtightness comparisons.
Question 6: What is the recommended approach for air sealing around recessed light fixtures in an insulated ceiling?
- Apply batt insulation directly over the fixtures
- Replace with IC-rated airtight (ICAT) fixtures or install a sealed cover box from above (Correct answer)
- Caulk around the visible trim ring from below
- Ensure a 3-inch clearance from insulation on all sides
Correct answer: Replace with IC-rated airtight (ICAT) fixtures or install a sealed cover box from above
ICAT-rated airtight fixtures or rigid foam cover boxes sealed from above eliminate the significant air leakage pathway that recessed lights create in ceilings.
Question 7: Which HVAC system configuration poses the greatest risk of envelope moisture problems in a very tight house?
- A fully ducted forced-air system with balanced supply and return
- An exhaust-only ventilation strategy without a dedicated fresh air intake (Correct answer)
- A mini-split heat pump with no ductwork
- A hydronic radiant floor system with a heat recovery ventilator
Correct answer: An exhaust-only ventilation strategy without a dedicated fresh air intake
Exhaust-only ventilation continuously depressurizes a tight house, drawing humid or contaminated outdoor air through uncontrolled leakage points throughout the envelope.
BPI Building Envelope 4
What does a window's U-factor measure?