InterNACHI Insulation and Ventilation 2 — Questions and Answers
Question 1: What is the primary purpose of a vapor retarder installed in a wall assembly?
- To increase the R-value of insulation
- To prevent moisture diffusion from warm to cold areas (Correct answer)
- To provide an air barrier against wind infiltration
- To reflect radiant heat back into the living space
Correct answer: To prevent moisture diffusion from warm to cold areas
A vapor retarder slows the movement of water vapor by diffusion from the warm, humid interior toward the cooler exterior where it could condense.
Question 2: Which ventilation ratio is the InterNACHI-accepted standard for attic ventilation when no vapor retarder is present in the ceiling?
- 1:150 (Correct answer)
- 1:300
- 1:600
- 1:900
Correct answer: 1:150
Without a vapor retarder in the ceiling, the required net free ventilation area increases to 1 square foot per 150 square feet of attic floor area.
Question 3: A home inspector observes fiberglass batt insulation installed without facing in a vented crawl space floor. What is the most likely concern?
- The R-value will be too high for the climate zone
- Insulation will eventually fall due to lack of support and contact loss (Correct answer)
- Vapor drive will be reversed causing exterior condensation
- The insulation will absorb formaldehyde from the subfloor
Correct answer: Insulation will eventually fall due to lack of support and contact loss
Unfaced batts installed between floor joists in a crawl space typically sag and fall over time, losing contact with the subfloor and greatly reducing effectiveness.
Question 4: What condition does the term 'thermal bypass' describe in an insulated building assembly?
- Heat conducted through a framing member rather than insulation
- Air movement around or through insulation reducing its effectiveness (Correct answer)
- A gap in insulation where two pieces fail to meet tightly
- Radiant heat transfer across an air space adjacent to insulation
Correct answer: Air movement around or through insulation reducing its effectiveness
A thermal bypass occurs when air moves through or around insulation, carrying heat with it and significantly degrading the assembly's overall thermal performance.
Question 5: Which type of insulation is most appropriate for sealing small irregular gaps around pipes and wiring penetrations through top plates?
- Rigid foam board cut to size
- Blown-in cellulose
- Two-component spray polyurethane foam (Correct answer)
- Fiberglass batt scraps
Correct answer: Two-component spray polyurethane foam
Two-component spray polyurethane foam expands to fill irregular shapes and adheres to most surfaces, making it ideal for air-sealing small penetrations.
Question 6: In a cathedral ceiling with no attic space, what minimum ventilation channel depth is typically required between the roof deck and insulation?
- 1/2 inch
- 1 inch (Correct answer)
- 2 inches
- 4 inches
Correct answer: 1 inch
Building codes and InterNACHI standards generally require a minimum 1-inch continuous air channel between the top of the insulation and the roof sheathing in cathedral ceiling assemblies.
Question 7: A home inspector finds that bathroom exhaust fans are ducted into the attic and terminate without an outlet. What deficiency does this represent?
- Insufficient CFM rating for the bathroom size
- Moisture-laden air is being discharged into the attic, promoting mold and rot (Correct answer)
- The duct material is incompatible with bathroom humidity levels
- Fire code requires metal duct, not flexible plastic
Correct answer: Moisture-laden air is being discharged into the attic, promoting mold and rot
Exhausting warm, moist bathroom air directly into the attic introduces significant moisture that can condense on structural members and sheathing, leading to mold, rot, and insulation damage.
InterNACHI Insulation and Ventilation 2
What is the primary purpose of a vapor retarder installed in a wall assembly?