BPI Building Envelope 3 — Questions and Answers
Question 1: What does the term 'dew point' represent in building envelope analysis?
- The temperature at which rain begins to form outdoors
- The temperature at which air becomes saturated and condensation begins (Correct answer)
- The outdoor temperature threshold for heating system activation
- The point at which insulation loses R-value from moisture
Correct answer: The temperature at which air becomes saturated and condensation begins
Dew point is the temperature at which air at a given moisture content reaches 100% relative humidity and condensation begins to form.
Question 2: In a BPI energy audit, which tool is used to identify air leakage sites by making leakage pathways visible?
- Combustion analyzer
- Blower door combined with smoke pencil or theatrical fog (Correct answer)
- Digital manometer alone
- Infrared camera used without a blower door
Correct answer: Blower door combined with smoke pencil or theatrical fog
A blower door depressurizes the house while a smoke pencil or fog machine makes air movement at leakage sites visible to the auditor.
Question 3: What is the primary advantage of closed-cell spray polyurethane foam (cc-SPF) over open-cell SPF in exterior wall cavities?
- Lower material cost per board foot
- Higher R-value per inch and acts as a vapor retarder (Correct answer)
- Better sound attenuation between rooms
- Faster installation in tight spaces
Correct answer: Higher R-value per inch and acts as a vapor retarder
Closed-cell SPF provides approximately R-6 to R-7 per inch and has a low permeance, making it function as a vapor retarder as well.
Question 4: Which building component is most commonly identified as a major unintentional air leakage pathway in older US homes?
- Double-pane window frames
- The top plate and band joist area (Correct answer)
- Exterior door weatherstripping
- Roof shingles
Correct answer: The top plate and band joist area
Top plates and band/rim joists are among the largest unintentional air leakage areas in older homes due to framing gaps and lack of sealing.
Question 5: What does a negative pressure reading in a combustion appliance zone (CAZ) during worst-case depressurization testing indicate?
- The appliance is operating at peak efficiency
- The zone is depressurized, which could cause backdrafting of combustion gases (Correct answer)
- Outdoor air is being properly supplied to the appliance
- The duct system is well-balanced
Correct answer: The zone is depressurized, which could cause backdrafting of combustion gases
Negative CAZ pressure during worst-case testing means appliances may be starved of combustion air and exhaust gases can backdraft into the living space.
Question 6: A homeowner reports ice dams forming at the eaves every winter. What is the primary building science cause?
- Insufficient roof pitch for the climate
- Heat loss through the ceiling warming the roof deck and melting snow that refreezes at cold eaves (Correct answer)
- Inadequate roof shingle quality
- Poor attic ventilation drawing cold outdoor air in
Correct answer: Heat loss through the ceiling warming the roof deck and melting snow that refreezes at cold eaves
Ice dams form when heat escaping through an inadequately insulated and air-sealed ceiling warms the roof deck, melting snow that flows to cold eaves and refreezes.
Question 7: What is the function of a 'drainage plane' in a wall assembly?
- To provide a thermal break between framing members
- To direct any water that penetrates the cladding away from the structure (Correct answer)
- To prevent vapor diffusion into the wall cavity
- To support the weight of exterior cladding
Correct answer: To direct any water that penetrates the cladding away from the structure
A drainage plane (weather-resistive barrier) directs incidental water that penetrates exterior cladding downward and out of the wall system.
BPI Building Envelope 3
What does the term 'dew point' represent in building envelope analysis?