Information about vapor barriers including discussions on wall designs, moisture balance, thermal characteristics, vapor permeance characteristics and recommendations by climate zone.
This paper discusses the differences between vented, unvented and conditioned crawl spaces. Best practice construction techniques and assemblies for conditioned crawl spaces are discussed, the results of a field monitoring program are presented, and the code language addressing crawl spaces is explained.
Good design and practice involve controlling the wetting of building assemblies from both the exterior and interior and different climates require different approaches.
The function of a vapor barrier is to retard the migration of water vapor. Where it is located in an assembly and its permeability is a function of climate, the characteristics of the materials that comprise the assembly and the interior conditions. Vapor barriers are not typically intended to retard the migration of air. That is the function of air barriers.
The current International Residential Code (IRC 2009) provides excellent guidance for the installation of vapor control layers.
Vapor barriers were originally intended to prevent assemblies from getting wet. Incorrect use of vapor barriers is leading to an increase in moisture-related problems.
