HERS HERS Thermal Envelope Insulation and Air Sealing 1 — Questions and Answers
Question 1: In HERS energy modeling, what is the thermal performance metric used to describe the insulating value of a wall assembly including all components?
- R-value
- U-factor
- Assembly R-value (whole-wall R-value) (Correct answer)
- C-value
Correct answer: Assembly R-value (whole-wall R-value)
Whole-wall or assembly R-value accounts for all components including framing, insulation, sheathing, and cladding for an accurate thermal performance measure.
Question 2: A HERS rater is inspecting a home with spray polyurethane foam (SPF) insulation in the roof deck. What ventilation configuration applies to this assembly?
- Vented attic with ridge and soffit vents
- Unvented conditioned attic — the HVAC system must be inside the thermal envelope (Correct answer)
- Ventilated crawl space below
- Vented cathedral ceiling with 1-inch airspace
Correct answer: Unvented conditioned attic — the HVAC system must be inside the thermal envelope
Spray foam applied to the roof deck creates an unvented conditioned attic, requiring that HVAC equipment and ducts be inside the thermal envelope.
Question 3: What is the RESNET-recognized default infiltration rate used for the Reference Home in HERS Index calculations?
- 3 ACH50
- 5 ACH50
- 7 ACH50 (Correct answer)
- 0.35 ACHn
Correct answer: 7 ACH50
RESNET uses 7 ACH50 as the default infiltration rate for the Reference Home when no blower door test is performed.
Question 4: Which area of a home typically accounts for the greatest air leakage in standard U.S. construction according to blower door diagnostic studies?
- Window and door frames
- Top plates and ceiling penetrations (Correct answer)
- Exterior wall sheathing seams
- Foundation sill plate
Correct answer: Top plates and ceiling penetrations
Top plates and ceiling penetrations (can lights, plumbing, wiring) are the largest source of air leakage in most U.S. homes.
Question 5: A HERS rater verifies continuous rigid foam insulation on the exterior of a wall assembly. What thermal performance benefit does this provide beyond cavity insulation alone?
- Increased vapor permeance
- Elimination of thermal bridging through framing members (Correct answer)
- Higher combustion safety margin
- Reduced blower door test time
Correct answer: Elimination of thermal bridging through framing members
Continuous exterior insulation eliminates thermal bridging through studs, dramatically improving whole-wall R-value.
Question 6: Under IECC 2021 for climate zone 5, what is the minimum required attic insulation R-value for a new home?
- R-38
- R-49 (Correct answer)
- R-60
- R-30
Correct answer: R-49
IECC 2021 requires a minimum of R-49 attic insulation in climate zone 5.
HERS HERS Thermal Envelope Insulation and Air Sealing 1
In HERS energy modeling, what is the thermal performance metric used to describe the insulating value of a wall assembly including all components?