InterNACHI Insulation and Ventilation 3 — Questions and Answers
Question 1: What is the R-value per inch for closed-cell spray polyurethane foam insulation?
- R-2 per inch
- R-3.5 per inch
- R-6 to R-7 per inch (Correct answer)
- R-10 per inch
Correct answer: R-6 to R-7 per inch
Closed-cell spray polyurethane foam typically provides R-6 to R-7 per inch, the highest R-value per inch among commonly used insulation types.
Question 2: Which condition is most likely to cause 'wind washing' in an attic insulation system?
- Ridge vent installed without baffles
- Inadequate soffit vent area compared to ridge vent area (Correct answer)
- Insufficient insulation depth at the attic floor center
- Blown insulation that is too dense to allow air movement
Correct answer: Inadequate soffit vent area compared to ridge vent area
When ridge vent area exceeds soffit vent area, negative pressure can draw outside air under the insulation at the eaves, degrading its R-value through wind washing.
Question 3: What does the 'net free area' of a vent refer to?
- The total face area of the vent cover
- The actual open area through which air can pass, excluding frame and screen (Correct answer)
- The required ventilation area minus existing ventilation already installed
- The attic floor area divided by the ventilation ratio
Correct answer: The actual open area through which air can pass, excluding frame and screen
Net free area is the actual unobstructed opening through which air flows, which is always less than the gross vent dimensions due to frames, louvers, and screens.
Question 4: A home inspector observes ice dams on the eaves of a house after a winter storm. Which attic condition most likely contributed to their formation?
- Excessive attic ventilation causing rapid heat loss
- Heat escaping through inadequate or missing attic insulation warming the roof deck (Correct answer)
- Ridge vents allowing warm exterior air into the attic during thaws
- Roof shingles with high solar absorptance retaining daytime heat
Correct answer: Heat escaping through inadequate or missing attic insulation warming the roof deck
Heat escaping from the living space through insufficient attic insulation warms the roof deck, melting snow that refreezes at the cold eaves and forms ice dams.
Question 5: What is the primary function of insulation baffles (rafter vents) installed in attic eave areas?
- To increase the R-value of insulation near the eaves
- To maintain a clear airway from soffit vents to the attic space above insulation (Correct answer)
- To prevent rodents from entering through soffit vents
- To redirect warm air from the living space toward the ridge
Correct answer: To maintain a clear airway from soffit vents to the attic space above insulation
Baffles create a channel that keeps soffit vent airflow clear of blown or batt insulation that might otherwise block the eave ventilation pathway.
Question 6: Which class of vapor retarder has a perm rating of 0.1 or less?
- Class I (Correct answer)
- Class II
- Class III
- Class IV
Correct answer: Class I
Class I vapor retarders, such as sheet polyethylene and glass, have a perm rating at or below 0.1, making them the most restrictive category.
Question 7: When inspecting a crawl space with a ground vapor barrier, what deficiency should an inspector note if the barrier is not sealed at the perimeter walls?
- The barrier will not reduce radon entry from soil gases
- Moisture will migrate from exposed soil edges into the crawl space air (Correct answer)
- The barrier is a fire hazard without perimeter attachment
- Unsealed edges allow pest entry under the barrier
Correct answer: Moisture will migrate from exposed soil edges into the crawl space air
Ground vapor barriers must be sealed or lapped up the foundation walls to prevent soil moisture from evaporating around the edges and entering the crawl space.
InterNACHI Insulation and Ventilation 3
What is the R-value per inch for closed-cell spray polyurethane foam insulation?