BPI Building Science & Envelope 4 — Questions and Answers
Question 1: What is the function of a 'rainscreen gap' in an exterior wall assembly?
- Providing structural support for cladding
- Creating a capillary break and drainage/drying space behind cladding (Correct answer)
- Improving the wall's overall R-value
- Reducing sound transmission through the wall
Correct answer: Creating a capillary break and drainage/drying space behind cladding
A rainscreen gap creates a pressure-equalized zone and capillary break that allows bulk water to drain and the assembly to dry.
Question 2: In building science, what does 'ACH50' represent?
- Air changes per hour at natural pressure
- Air changes per hour at 50 Pascals depressurization (Correct answer)
- Average CFM of infiltration over 50 hours
- Allowable air changes per hour for code compliance at standard pressure
Correct answer: Air changes per hour at 50 Pascals depressurization
ACH50 is the number of times per hour the entire volume of a house's air is replaced when the building is depressurized to 50 Pascals by a blower door.
Question 3: What is 'thermal mass' and how does it affect a building's energy performance?
- The total weight of insulation installed, which reduces heat loss
- The capacity of dense materials to store heat, moderating temperature swings (Correct answer)
- The R-value contribution of structural framing members
- The heat generated by occupants and appliances
Correct answer: The capacity of dense materials to store heat, moderating temperature swings
Thermal mass materials like concrete and brick absorb heat during the day and release it at night, reducing peak heating and cooling loads.
Question 4: Which of the following best describes the 'stack effect' in a tall building?
- Hot air rising and cold air sinking within wall cavities only
- Pressure difference between indoors and outdoors caused by temperature-driven buoyancy forces (Correct answer)
- The accumulation of combustion gases near the ceiling
- Increased wind pressure on the windward face of the building
Correct answer: Pressure difference between indoors and outdoors caused by temperature-driven buoyancy forces
Stack effect occurs when temperature differences between inside and outside create buoyancy-driven pressure differences, drawing air in at low points and out at high points in winter.
Question 5: A BPI assessor finds that a crawl space has exposed soil and open vents to the outside. What is the MOST effective moisture control upgrade?
- Installing a dehumidifier only
- Sealing vents, installing a ground vapor barrier, and conditioning or encapsulating the space (Correct answer)
- Adding more ventilation to dilute moisture
- Insulating the crawl space floor joists with fiberglass batts
Correct answer: Sealing vents, installing a ground vapor barrier, and conditioning or encapsulating the space
Encapsulating the crawl space by sealing vents, covering soil, and conditioning the space dramatically reduces moisture entry and related problems.
Question 6: What is the purpose of 'thermal bridging' identification during a BPI energy audit?
- Finding locations where air leakage occurs through thermal bypasses
- Identifying conductive pathways that bypass insulation and significantly reduce effective assembly R-value (Correct answer)
- Locating ductwork within unconditioned spaces
- Detecting radiant heat loss through windows
Correct answer: Identifying conductive pathways that bypass insulation and significantly reduce effective assembly R-value
Thermal bridges are conductive paths (framing, fasteners, structural elements) that bypass insulation, reducing the overall effective thermal resistance of an assembly.
Question 7: When using an infrared camera during a BPI energy audit, what indoor-to-outdoor temperature difference is generally considered the minimum for reliable results?
- 5°F (3°C)
- 10°F (6°C)
- 18°F (10°C) (Correct answer)
- 30°F (17°C)
Correct answer: 18°F (10°C)
A temperature differential of at least 18°F (10°C) between indoors and outdoors is generally required to produce reliable thermal imaging results.
BPI Building Science & Envelope 4
What is the function of a 'rainscreen gap' in an exterior wall assembly?