This paper presents experimental test results for heat and moisture migration in walls exposed to hot and humid climates. The research was conducted to study the problem of mold and mildew caused by moisture transfer into walls of concrete masonry unit (CMU) type construction by diffusion and convective transport by air infiltration. This type of construction is common in commercial buildings in the southern United States. The tests were conducted in two phases. Phase 1 evaluated heat and moisture transfer by diffusion. Phase 2 testing involved air infiltration through the test walls. Data were also collected to determine the rate at which the test walls would dry out without infiltration present. Test results indicate that an exterior vapor retarder will reduce the moisture migration into the wall and thereby lower the moisture accumulation due to infiltration when a vapor retarder (such as vinyl wallpaper) is used for the interior surface treatment. Testing also showed that while the exterior wall treatment does have an effect on reducing the total moisture accumulation in the test walls, the interior wall treatment has a much larger impact when infiltration is present. The data support a proposed criterion for the onset of mold and mildew, which requires a monthly average surface relative humidity of 80% with temperatures between 32°F and 105°F (0°C and 40.6°C).

Units: Dual