BPI Building Envelope 2

Question 1

What is the primary purpose of a vapor retarder in a wall assembly?

Accepted Answer

To limit moisture diffusion through the assembly

Answer

A vapor retarder limits moisture vapor diffusion through the building envelope, reducing condensation risk within wall cavities.

Question 2

In a hot-humid climate, where should the vapor retarder typically be placed in a wall assembly?

Accepted Answer

On the exterior (warm-in-summer) side

Answer

In hot-humid climates, moisture drives inward from outside, so the vapor retarder belongs on the exterior side of the assembly.

Question 3

Which blower door metric directly represents building airtightness normalized by conditioned floor area?

Accepted Answer

CFM50

Answer

CFM50 per square foot of conditioned floor area is the standard BPI metric for normalizing airtightness to floor area.

Question 4

A 'thermal bridge' in a wall assembly most commonly results in which problem?

Accepted Answer

Localized cold spots that can lead to condensation and mold

Answer

Thermal bridges conduct heat faster than surrounding materials, creating cold interior surface spots where condensation and mold can develop.

Question 5

What does 'stack effect' refer to in building science?

Accepted Answer

Pressure difference caused by indoor/outdoor temperature difference driving air movement

Answer

Stack effect is the buoyancy-driven pressure difference between indoor and outdoor air caused by temperature (and thus density) differences.

(BPI) Building Performance Institute Certified Practice Test