Cross-laminated timber (CLT) is one of the widely used engineered wood products in mass timber construction. It has successfully penetrated the European construction market over the past two decades. Its sustainable characteristics provide major advantages over other construction materials. Its susceptibility to biological degradation is a concern for architects, engineers, and builders, especially in regions with high termite infestation and fungal decay risks. Because such degradation is often driven by moisture, temperature, and nutrient accessibility, a comprehensive understanding of how heat and moisture move through exterior CLT wall envelope systems is needed to optimize design strategies.