CEM Building Envelope and Insulation 2 — Questions and Answers
Question 1: Degree days are used in building energy analysis to:
- Measure indoor air quality over time
- Quantify heating or cooling demand based on outdoor temperature deviation from a base (Correct answer)
- Calculate peak electrical demand
- Estimate solar radiation available for daylighting
Correct answer: Quantify heating or cooling demand based on outdoor temperature deviation from a base
Heating degree days (HDD) and cooling degree days (CDD) accumulate daily temperature differences from a base (usually 65°F) to estimate seasonal heating and cooling energy needs.
Question 2: Which roof assembly strategy best reduces cooling loads in a hot climate?
- Dark-colored ballasted roof membrane
- Cool (high-reflectance, high-emittance) roof surface (Correct answer)
- Unvented attic with no insulation
- Increasing roof thermal mass only
Correct answer: Cool (high-reflectance, high-emittance) roof surface
Cool roofs with high solar reflectance and thermal emittance reduce roof surface temperatures, lowering heat conduction into the building and reducing cooling energy use.
Question 3: Adding continuous exterior insulation to a wall assembly primarily helps by:
- Increasing visible light transmittance of the wall
- Eliminating thermal bridging through framing members (Correct answer)
- Reducing the wall's thermal mass
- Increasing air infiltration for ventilation
Correct answer: Eliminating thermal bridging through framing members
Continuous exterior insulation wraps the entire wall face including studs, eliminating thermal bridges at framing and significantly improving whole-wall R-value.
Question 4: Fenestration area strongly affects building energy use because windows typically have:
- Higher R-values than opaque walls
- Much lower R-values than insulated walls, increasing heat transfer significantly (Correct answer)
- No effect on solar heat gain
- Higher thermal mass than masonry walls
Correct answer: Much lower R-values than insulated walls, increasing heat transfer significantly
Even high-performance triple-pane windows have U-factors around 0.15-0.20 (R-5 to R-7), far lower than typical insulated walls at R-20 or higher, making windows a major heat loss/gain pathway.
Question 5: Vapor retarders in wall assemblies are installed to:
- Increase air infiltration rates
- Control moisture diffusion and prevent condensation within the wall cavity (Correct answer)
- Improve the fire rating of the wall
- Reduce sound transmission through the wall
Correct answer: Control moisture diffusion and prevent condensation within the wall cavity
Vapor retarders slow water vapor diffusion through walls, preventing moisture from condensing within the assembly and causing mold, rot, or insulation degradation.
Question 6: The stack effect in tall buildings causes energy losses because:
- Warm air rises and escapes at the top, drawing cold outside air in at the bottom (Correct answer)
- Cold air sinks and cools the ground floor more than upper floors
- Pressure differences cause windows to vibrate and lose U-factor
- Stack effect increases lighting loads on upper floors
Correct answer: Warm air rises and escapes at the top, drawing cold outside air in at the bottom
In winter, warm buoyant air rises and leaks out at upper floors, while cold outdoor air infiltrates at lower levels, increasing heating loads significantly in tall buildings.
CEM Building Envelope and Insulation 2
Degree days are used in building energy analysis to: