HERS Building Science Principles 3 — Questions and Answers
Question 1: How does wind-driven rain most commonly enter a wall assembly in a climate with high wind exposure?
- Vapor diffusion through exterior sheathing
- Capillary action through the sill plate
- Forced water entry through gaps and cracks under pressure (Correct answer)
- Condensation on the back side of the cladding
Correct answer: Forced water entry through gaps and cracks under pressure
Wind pressure forces liquid water through gaps, cracks, and penetrations in the cladding and air barrier under positive pressure.
Question 2: What is 'interstitial condensation' in a building assembly?
- Condensation on interior glass surfaces
- Condensation forming within the layers of a wall, roof, or floor assembly (Correct answer)
- Condensation on exterior foundation walls below grade
- Condensation in ductwork caused by oversized cooling equipment
Correct answer: Condensation forming within the layers of a wall, roof, or floor assembly
Interstitial condensation occurs inside the building assembly layers when vapor migrates to a surface that is at or below the dew point.
Question 3: A building with tight construction and mechanical ventilation exemplifies which principle from ASHRAE 62.2?
- Build loose, ventilate naturally
- Build tight, ventilate right (Correct answer)
- Balanced pressure at all times
- Maximum infiltration for indoor air quality
Correct answer: Build tight, ventilate right
ASHRAE 62.2 embraces the 'build tight, ventilate right' approach, using controlled mechanical ventilation instead of uncontrolled air leakage.
Question 4: Which type of foundation is most susceptible to ground moisture intrusion by capillary action?
- Elevated post-and-beam foundation
- Slab-on-grade without capillary break (Correct answer)
- Basement with exterior waterproofing membrane
- Crawlspace with closed-cell spray foam on walls
Correct answer: Slab-on-grade without capillary break
Concrete slabs placed directly on soil without a capillary break (gravel layer or poly film) allow moisture to wick upward continuously.
Question 5: In whole-building energy modeling, what does the term 'internal gains' refer to?
- Solar radiation entering through south-facing windows
- Heat generated inside the building by occupants, lighting, and appliances (Correct answer)
- Heat conducted inward through the building envelope
- Sensible heat produced by the heating system itself
Correct answer: Heat generated inside the building by occupants, lighting, and appliances
Internal gains are heat sources within the conditioned space—occupants, lights, cooking, and plug loads—that contribute to the cooling load.
Question 6: What is the function of a 'drain plane' or 'drainage plane' in a wall assembly?
- To direct electrical conduit away from insulation
- To channel any water that gets past the cladding back out of the assembly (Correct answer)
- To reduce vapor diffusion through the wall cavity
- To provide a thermal break between the stud and exterior sheathing
Correct answer: To channel any water that gets past the cladding back out of the assembly
A drainage plane (housewrap, building paper, or similar) sheds water that penetrates the cladding and directs it out of the wall system.
Question 7: Which metric is used to quantify the airtightness of a building in a blower door test?
- CFM50 or ACH50 (Correct answer)
- MERV rating
- Latent heat ratio
- Net free area per square foot
Correct answer: CFM50 or ACH50
Blower door results are reported as CFM50 (cubic feet per minute at 50 Pa) or ACH50 (air changes per hour at 50 Pa depressurization.
HERS Building Science Principles 3
How does wind-driven rain most commonly enter a wall assembly in a climate with high wind exposure?