Insulation and Ventilation Flashcards

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?

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.

Fiberglass batts in an attic have been compressed to half their thickness by stored boxes. How does this affect performance?

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.

Which insulation material typically provides the highest R-value per inch?

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.

Exposed spray foam insulation covers the walls of a finished basement recreation room. What should the inspector note?

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.

In a vented crawlspace with fiberglass batts between the floor joists, which way should the kraft facing face?

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.

An inspector finds active knob-and-tube wiring buried under blown-in insulation in an attic. What is the appropriate recommendation?

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.

Rigid or semi-rigid metal duct is required for a clothes dryer exhaust mainly because:

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.