HERS Building Envelope & Insulation 3 â Questions and Answers
Question 1: What is the purpose of a wind-washing barrier behind insulation in an attic knee wall?
- To increase R-value by trapping air
- To prevent wind from reducing insulation effectiveness (Correct answer)
- To serve as a vapor retarder
- To reflect radiant heat from the roof
Correct answer: To prevent wind from reducing insulation effectiveness
Wind washing occurs when air movement through insulation reduces its thermal resistance; a rigid barrier on the cold side prevents this.
Question 2: Which climate zone(s) typically require a continuous air barrier but NOT a vapor retarder on the interior?
- Climate Zones 1-2 (hot-humid) (Correct answer)
- Climate Zones 5-8 (cold)
- All climate zones require both
- No climate zones require an air barrier
Correct answer: Climate Zones 1-2 (hot-humid)
In hot-humid climates, interior vapor retarders can trap moisture inside assemblies; an air barrier alone is the recommended moisture control strategy.
Question 3: What is the minimum net free area ratio required for ventilation chutes (baffles) in a vented attic per IRC?
- 1:100 of conditioned floor area
- 1:150 of the attic floor area (Correct answer)
- 1:300 of the attic floor area
- 1:500 of the attic floor area
Correct answer: 1:150 of the attic floor area
IRC Section R806 requires a minimum net free ventilating area of 1:150 unless conditions allow 1:300 with balanced high/low distribution.
Question 4: In HERS ratings, what is the correct term for the total area of all surfaces separating conditioned space from unconditioned space or outdoors?
- Thermal envelope area (Correct answer)
- Conditioned floor area
- Gross wall area
- Building shell perimeter
Correct answer: Thermal envelope area
The thermal envelope encompasses all surfacesâwalls, roof, floors, windows, and doorsâthat bound the conditioned space.
Question 5: A rim joist is a common air leakage site in older homes. Which insulation method best addresses both air sealing and thermal performance at the rim joist?
- Fiberglass batt cut to fit loosely
- Spray foam applied directly to the rim joist (Correct answer)
- Rigid foam board with no sealant
- Cellulose blown into the joist bay
Correct answer: Spray foam applied directly to the rim joist
Spray foam conforms to irregular surfaces, seals all gaps, and provides insulation in a single step, making it ideal for rim joists.
Question 6: What does the term 'effective R-value' account for that nominal R-value does not?
- Material cost and installation labor
- Thermal bridging through framing members (Correct answer)
- Insulation thickness only
- R-value at different outdoor temperatures
Correct answer: Thermal bridging through framing members
Effective R-value accounts for the reduced whole-assembly thermal resistance caused by thermal bridging through studs, joists, and other framing elements.
Question 7: Which of the following is classified as an air-impermeable insulation per ASTM E2178?
- Unfaced fiberglass batt
- Blown cellulose
- Closed-cell spray polyurethane foam (Correct answer)
- Mineral wool batt
Correct answer: Closed-cell spray polyurethane foam
Closed-cell spray foam has an air permeance â¤0.02 L/(s¡m²) at 75 Pa, meeting the ASTM E2178 definition of air-impermeable insulation.
HERS Building Envelope & Insulation 3
What is the purpose of a wind-washing barrier behind insulation in an attic knee wall?