A difference in temperature, air pressure, and humidity between the inside and outside of the home will create a pathway for warm, moist air, which will condense as it contacts colder surfaces. If this is not addressed quickly, moisture damage within a wall is inevitable, and the occupants may not be aware that mold spores, like rotting studs, or saturated insulation may be developing.
Pathways for airflow can result where two dissimilar materials come together in a building envelope, i.e., where the often-uneven concrete foundation ends and the wood-framed wall begins or where a recessed light fixture sits within a framed and drywalled ceiling. That’s why the integration of the building materials—often more than the choice of product itself—are crucial in preventing this and other problems.
In all cases, the control mechanisms for heat, air, and moisture must work together. Additionally, wall designs, materials, and system choices need to be climate- and site-specific.
In this 1980s-era home built in Ontario, Canada, moisture-laden interior air is exfiltrating through and around an electrical outlet on an exterior wall and condensing on the back side of OSB sheathing, leading to material degradation.