Review on ventilation rates in the ventilated air-spaces behind common wall assemblies with external cladding

For many decades, ventilated cavities in wall assemblies of buildings have been essential for creating moisture resilient constructions by allowing airflow within the air gap to promote drying. In addition to that, the airflow in the cavity can enhance the thermal performance of the building envelope, depending on the air change rate and outdoor conditions. Therefore, the effective factors on the air change rate in the ventilated cavity behind common wall assemblies with external cladding are specified in the present study. As a first step, the analysis of the stack effect and wind effect as mechanisms that drive the airflow in the ventilated air-space available in the literature is reviewed. Moreover, the hydraulic network of pressure losses along the wall cavity is analyzed, and various correlations for the loss factors are described. Despite separate studies analyzing the effect of the ventilated cavity on moisture dissipation through water-permeable materials, a comprehensive overview of the airflow rates behind the ventilated wall assemblies is still lacking. Therefore, as the second step in this paper, existing methods of predicting air-change rates behind the ventilated cladding systems are classified and compared with the measured data. The amount of air change rate in the ventilated air gaps behind brick, cement & stucco, ceramic, wood, and other types of external facades are studied through a comprehensive review of relevant publications. Based on the observations, the maximum air change rate in the air-spaces behind open joint claddings such as the ceramic wall is nearly two times compared to the closed joint claddings such as the brick wall.