Unintentional airflow in exterior framed walls frequently causes diminished thermal performance. Furthermore, even very small infiltrative or exfiltrative airflows with little or no effect on the thermal performance are capable of voiding the moisture protection provided by a vapor retarder. Combined with high indoor or outdoor humidity, such walls may accumulate excessive amounts of moisture. However, more data were needed on airflows in and through wall assemblies and the effect of airflows on moisture conditions in walls. Twenty wood frame walls of ten different designs, characteristic of walls of manufactured homes, were constructed and installed in a test building near Madison, Wisconsin. In-place pressurization and depressurization tests were performed to separately determine airtightness of the interior and exterior membranes of the wall. This paper describes the methodology, equipment, and results of these measurements. Air pressure differences across these walls were monitored during an entire winter season, along with temperatures and moisture conditions in the walls. This paper describes the instrumentation and methodology used in these measurements. The measurements showed that providing wall cavity ventilation may cause pressurization of the wall cavity and can lead to a significant increase in air leakage and heat loss without reliably providing the intended protection from moisture accumulation in the cavity. Although several of the walls experienced condensation and mold growth, the moisture conditions in the walls showed no clear correlation with airtightness or with the amount of air flowing through the wall. Indoor humidity correlated strongly with wall cavity moisture conditions, suggesting that indoor humidity control is the most effective strategy to prevent excessive moisture accumulation in the exterior building envelope during winter.