Moisture Control Designs for Hot and Humid Climates
In hot, humid southern climates, where moisture is a concern during the summer, the vapor barrier is installed at the exterior of the wall system (Figure 5). This layer is frequently a multipurpose material providing an air, water, and vapor barrier. Any breaks in this barrier will allow air and vapors to enter the cavity. The temperature of the metal studs can be below the dew point when adjacent to interior gypsum, and condensation will form, causing corrosion, along with insulation and gypsum board deterioration problems.

Figure 5 Section detail of typical warm climate multi-component wall system.

Moisture Control Designs for Moderate Zones
In moderate climate zones throughout the U.S., a "smart" vapor barrier is often installed in the wall system (Figure 6). It is typically located on the interior of the studs and has characteristics that allow variable amounts of air and water permeability. When installed correctly, the perm rating actually changes with the change of relative humidity. During the winter when RH is low, the perm rating is 1, and during the summer with high RH the perm rating changes to 10 (Figure 6, Centria #9).

Figure 6 Section detail of typical moderate climate multi component wall system.

4. Multi Component Wall Systems

Multi-component wall systems are made up of numerous individual components that require careful design attention in order to avoid some common challenges related to thermal, moisture, and structural concerns. Typical components and concerns include: