BPI Building Science & Envelope 2

Question 1

Which phenomenon causes moisture to migrate from areas of high vapor pressure to low vapor pressure through building materials?

Accepted Answer

Vapor diffusion

Answer

Vapor diffusion is the movement of water vapor through materials driven by differences in vapor pressure, independent of air movement.

Question 2

What is the primary purpose of a drainage plane in a wall assembly?

Accepted Answer

Directing bulk water away from the structure

Answer

A drainage plane sheds bulk water that penetrates the outer cladding and directs it down and out of the wall assembly.

Question 3

In a mixed-humid climate (IECC Zone 4A), where is the recommended location for the primary vapor retarder in a wall assembly?

Accepted Answer

No vapor retarder is required

Answer

In Zone 4A mixed-humid climates, a Class III vapor retarder (or none) is often acceptable because moisture drive reverses seasonally.

Question 4

What is the 'dew point' in the context of building science?

Accepted Answer

The temperature at which air becomes fully saturated and condensation begins

Answer

The dew point is the temperature to which air must be cooled at constant pressure for water vapor to condense into liquid.

Question 5

Which insulation material has the highest resistance to vapor diffusion per inch of thickness?

Accepted Answer

Closed-cell spray polyurethane foam

Answer

Closed-cell SPF has a very low perm rating (approximately 0.8–1.5 perms at 2 inches), making it highly resistant to vapor diffusion.

(BPI) Building Performance Institute Certified Practice Test