Dynamic Thermal Performance Degradation of Building Envelopes Under Wind-Driven Rain: A Cross-Climatic Comparative Analysis

Conventional building codes rely on standard dry-state conditions, systematically underestimating thermal degradation induced by wind-driven rain. To address this, this study establishes a dynamic evaluation framework to quantify moisture-induced deviations and re-rank the hygrothermal adaptability of representative wall assemblies. Transient hygrothermal simulations were conducted on 68 cases, encompassing five wall configurations across four diverse Chinese thermal design zones. Results demonstrate significant thermal degradation under long-term rain exposure, with actual annual average dynamic U-values reaching a mean of 1.25 W/(m2·K) and exceeding design baselines for 6.15 months. Results show that this degradation follows a geographical gradient, escalating from minor deviations in Severe Cold zones to systemic failure in Hot Summer and Cold Winter zones, where the mean dynamic U-value surges to 2.20 W/m2K. Deterioration is episodic, with peak monthly U-values reaching 16.21 W/(m2·K) during transitional months like June and October, often accompanied by heat flow reversals. The dynamic evaluation shatters normative compliance parity, refining uniform applicability into a definitive performance hierarchy ranging from resilient wall assembly of Type 2 to vulnerable Type 4. Findings highlight that future envelope design must pivot from binary normative compliance toward comprehensive dynamic hygrothermal assessments to ensure genuine climate resilience in practice.