Understanding the Benefit of Ventilation in Stucco Assemblies

In North America, stucco is a widely used and growing exterior cladding in residential construction, comprising 24% of the US primary exterior wallmaterial in 2015, up from 16% in 1995, according to the US Census Bureau. Stucco use is regional being concentrated in the West (56% in 2015)and South (21%). Despite stucco’s popularity over the last 20 years, stucco systems have been associated with several performance challenges includingcracking and water intrusion. To respond to the performance challenges, proposals requiring ventilation behind the stucco have been proposed to codes andstandards in the USA. Additionally, new products have been introduced to facilitate back-ventilation of stucco. Products designed to provide behindcladding ventilation were tested for airflow under static air pressure difference as measured by ASTM E2925-17 Standard Specification forManufactured Polymeric Drainage and Ventilation Materials Used to Provide a Rainscreen Function. The experimental data was used in conjunctionwith reported field air pressure differences to inform a parametric modeling study. The goal of the modeling study was to better understand the moistureperformance benefits of stucco back-ventilation. The study included the effects of climate, stucco material properties and other assembly characteristics.