HERS Building Science Principles 2 — Questions and Answers
Question 1: Which phenomenon causes warm, moist air to condense on a cold surface inside a wall assembly?
- Thermal bridging
- Dew point condensation (Correct answer)
- Stack effect pressure
- Vapor diffusion equilibrium
Correct answer: Dew point condensation
When air cools to its dew point temperature at a cold surface, water vapor condenses into liquid moisture.
Question 2: In a hot-humid climate, where should the vapor retarder be placed in a wall assembly?
- On the interior (warm-in-winter) side
- In the center of the cavity
- On the exterior side, toward the hot exterior (Correct answer)
- No vapor retarder is needed in hot-humid climates
Correct answer: On the exterior side, toward the hot exterior
In hot-humid climates, the dominant moisture drive is inward from the hot exterior, so the vapor retarder belongs on the exterior side.
Question 3: What does the term 'thermal mass' refer to in building science?
- The total weight of insulation in a wall
- A material's ability to store and slowly release heat (Correct answer)
- The R-value of a dense-pack insulation product
- The ratio of conduction to convection in a building envelope
Correct answer: A material's ability to store and slowly release heat
Thermal mass describes a material's capacity to absorb, store, and release heat energy, moderating interior temperature swings.
Question 4: Which heat transfer mechanism does low-emissivity (low-e) window coating primarily reduce?
- Conduction through the glass
- Convection at the glass surface
- Radiation across the air gap (Correct answer)
- Air infiltration around the frame
Correct answer: Radiation across the air gap
Low-e coatings reflect infrared radiation, reducing the radiative heat transfer between the glass panes.
Question 5: A HERS rater measures attic ventilation to ensure balance between intake and exhaust. What is the recommended ratio of net free area to attic floor area when using balanced ventilation?
- 1:100
- 1:150 (Correct answer)
- 1:300
- 1:600
Correct answer: 1:150
The standard building code ratio for balanced attic ventilation (50% intake, 50% exhaust) is 1:150 net free area to floor area.
Question 6: What is the primary purpose of an air barrier in a building enclosure?
- To prevent vapor diffusion through materials
- To resist convective air movement through the building shell (Correct answer)
- To add R-value to wall assemblies
- To control solar heat gain through windows
Correct answer: To resist convective air movement through the building shell
An air barrier controls convective airflow (infiltration and exfiltration) through the building envelope, not diffusion.
Question 7: Which condition best describes a 'negative pressure' house?
- Interior air pressure is higher than exterior pressure
- Interior air pressure is lower than exterior pressure (Correct answer)
- Pressure is equal on all sides of the envelope
- The HVAC system is over-sized for the heating load
Correct answer: Interior air pressure is lower than exterior pressure
A negative pressure building has interior pressure below outdoor pressure, causing outdoor air to be drawn inward through any gaps.
HERS Building Science Principles 2
Which phenomenon causes warm, moist air to condense on a cold surface inside a wall assembly?