Vapor retarders

In this section, a ceiling assembly separates the attic space above from the room interior below. If the building is located in Lewisville, Texas (hot-humid zone), where is the predicted location of condensation and what is the predicted condition of the gypsum board in this assembly? (Select 2 from the following)

A. outside face of vapor retarder
B. inside face of vapor retarder
C. gypsum board will be wet
D. gypsum board will be dry



Answer: A. and C. As Lewisville is a hot-humid location, expect the room interior to be cooled by air-conditioning. Kraft paper facing acts as a vapor retarder with predictable condensation on the outside face, but this is faced on both sides - so the gyp. board will be wet. The vapor retarder should only be located outside of the insulation or between the insulation and the ventilated attic space.

Visit the PPD-PDD page for more study resources!

Reference tip: read a paper about air vs vapor barriers here from conference session E11: Performance of the Building Enclosure of the 2008 Best 1 Conference BEST = Building Enclosure Science & Technology from National Institute of Building Sciences.