NHIE Insulation and Ventilation 5 — Questions and Answers
Question 1: An inspector notices that a powered attic ventilator is installed in a tightly sealed home with a natural-draft gas water heater. What hazard should be considered?
- The fan can depressurize the house through ceiling leaks and cause backdrafting of combustion gases (Correct answer)
- The fan will overheat the roof shingles
- The fan will lower the water heater's efficiency rating
- There is no interaction between attic fans and appliances
Correct answer: The fan can depressurize the house through ceiling leaks and cause backdrafting of combustion gases
If the attic is not sealed from the living space, a powered ventilator can pull conditioned air out of the house and reverse flue draft.
Question 2: Fiberglass batts in an attic have been compressed to half their thickness by stored boxes. How does this affect performance?
- R-value increases because the material is denser
- R-value is unaffected because the fiber count is the same
- Total R-value is reduced because the trapped air spaces are lost (Correct answer)
- The batts become a vapor retarder
Correct answer: Total R-value is reduced because the trapped air spaces are lost
Fiberglass insulates by trapping air, so compressing it lowers its total R-value.
Question 3: Which insulation material typically provides the highest R-value per inch?
- Loose-fill fiberglass
- Closed-cell spray polyurethane foam (Correct answer)
- Blown cellulose
- Mineral wool batts
Correct answer: Closed-cell spray polyurethane foam
Closed-cell spray foam is roughly R-6 to R-7 per inch, compared with about R-2.5 to R-4 for fiberglass, cellulose, and mineral wool.
Question 4: Exposed spray foam insulation covers the walls of a finished basement recreation room. What should the inspector note?
- Nothing; spray foam is noncombustible
- It needs a coat of latex paint only
- It should be covered with a vapor barrier
- It generally requires a thermal barrier such as 1/2-inch drywall (Correct answer)
Correct answer: It generally requires a thermal barrier such as 1/2-inch drywall
Foam plastic insulation in habitable spaces must generally be separated from the interior by an approved thermal barrier such as 1/2-inch gypsum board.
Question 5: In a vented crawlspace with fiberglass batts between the floor joists, which way should the kraft facing face?
- Up, toward the heated subfloor (Correct answer)
- Down, toward the crawlspace soil
- Either way; the facing is purely cosmetic
- Toward the nearest foundation vent
Correct answer: Up, toward the heated subfloor
The vapor retarder facing belongs on the warm-in-winter side, which in a crawlspace floor is the subfloor above.
Question 6: An inspector finds active knob-and-tube wiring buried under blown-in insulation in an attic. What is the appropriate recommendation?
- No concern, because insulation protects the wires
- Recommend sealing the wires with spray foam
- Recommend evaluation by a licensed electrician because buried knob-and-tube can overheat (Correct answer)
- Recommend adding a vapor barrier over the wiring
Correct answer: Recommend evaluation by a licensed electrician because buried knob-and-tube can overheat
Knob-and-tube wiring was designed to shed heat into open air, so covering it with insulation creates an overheating and fire risk.
Question 7: Rigid or semi-rigid metal duct is required for a clothes dryer exhaust mainly because:
- It is cheaper than vinyl duct
- It resists fire and has a smooth interior that limits lint buildup (Correct answer)
- It allows the dryer to vent into the attic safely
- It eliminates the need for an exterior termination
Correct answer: It resists fire and has a smooth interior that limits lint buildup
Plastic or foil duct can sag, trap lint, and burn, while metal duct with a smooth interior lowers the fire risk.
