BAP Building Envelope & Insulation 2 — Questions and Answers
Question 1: What is the primary benefit of installing continuous insulation (ci) on the exterior of a wall assembly?
- It increases the structural load-bearing capacity of the wall
- It eliminates thermal bridging through the framing members (Correct answer)
- It serves as the primary vapor retarder for the assembly
- It replaces the need for cavity insulation between studs
Correct answer: It eliminates thermal bridging through the framing members
Continuous exterior insulation covers the framing members, eliminating the thermal bridges that studs or metal tracks create in a standard cavity-insulated wall.
Question 2: What does the metric ACH50 represent in a blower door test?
- Total conditioned air volume exchanged per hour at normal conditions
- Air changes per hour measured at a depressurization of 50 Pascals (Correct answer)
- Average cubic feet per minute at 50% relative humidity
- Air conditioning capacity required at an outdoor temperature of 50°F
Correct answer: Air changes per hour measured at a depressurization of 50 Pascals
ACH50 (Air Changes per Hour at 50 Pascals) is the standardized blower door metric that quantifies envelope airtightness by relating total air leakage to building volume.
Question 3: In a vented attic assembly, at what plane should the air barrier be installed?
- At the roof deck, beneath the sheathing
- At the ceiling plane — the floor of the attic above conditioned space (Correct answer)
- At the mid-depth of the attic insulation layer
- At the soffit, to direct airflow into the attic
Correct answer: At the ceiling plane — the floor of the attic above conditioned space
In a vented attic the air barrier belongs at the ceiling plane to prevent conditioned air from escaping into the unconditioned attic space where it could cause moisture problems.
Question 4: Kraft-faced fiberglass batt insulation is classified under building codes as which class of vapor retarder?
- Class I (≤0.1 perms)
- Class II (0.1–1.0 perms) (Correct answer)
- Class III (1.0–10 perms)
- Vapor-open (>10 perms)
Correct answer: Class II (0.1–1.0 perms)
Kraft facing on fiberglass batts has a permeance rating between 0.1 and 1.0 perms, placing it in the Class II vapor retarder category under the IRC and IECC.
Question 5: How does the stack effect influence air leakage through a building envelope?
- Warm air rises creating positive pressure at the top and negative pressure at the bottom, driving infiltration and exfiltration (Correct answer)
- Cool air sinks creating positive pressure at the base, pushing air upward through the envelope uniformly
- The stack effect only influences air movement in duct systems, not through the envelope
- It creates equal pressure across all elevations, producing uniform air leakage
Correct answer: Warm air rises creating positive pressure at the top and negative pressure at the bottom, driving infiltration and exfiltration
The stack effect results from buoyancy of warm air — positive pressure at upper levels drives exfiltration through the top of the envelope, while negative pressure at lower levels drives infiltration at the base.
Question 6: What is the most effective method for insulating and air sealing rim joists in existing homes?
- Leave uninsulated to allow drying to the exterior
- Install cut-and-cobbled rigid foam boards without additional air sealing
- Apply closed-cell spray polyurethane foam to simultaneously insulate and air seal (Correct answer)
- Stuff fiberglass batts into the rim joist cavity without sealing the edges
Correct answer: Apply closed-cell spray polyurethane foam to simultaneously insulate and air seal
Closed-cell SPF is the preferred rim joist treatment because a single application provides both insulation (R-6+/inch) and a complete air seal in this irregularly shaped, high-loss area.
Question 7: What is the primary function of a drainage plane (water-resistive barrier) in a wall assembly?
- To prevent all exterior moisture from ever penetrating behind the cladding
- To redirect any water that does penetrate the cladding back to the exterior (Correct answer)
- To serve as the primary vapor retarder for the wall assembly
- To provide supplemental insulating value to the exterior wall
Correct answer: To redirect any water that does penetrate the cladding back to the exterior
A drainage plane (WRB) manages water that gets behind the cladding by providing a surface to drain it down and out, recognizing that no cladding system is perfectly waterproof.
BAP Building Envelope & Insulation 2
What is the primary benefit of installing continuous insulation (ci) on the exterior of a wall assembly?