A practical engineering method to map microclimate-driven degradation risks on building façades

Journal article, 2026

Assessing moisture-induced degradation risks across façades typically relies on Computational Fluid Dynamics (CFD) to resolve wind-driven rain (WDR) distribution and spatially varying microclimate conditions. This paper presents an alternative engineering-based methodology combining semi-empirical WDR models with detailed solar irradiation analysis to derive spatially varying boundary conditions for hygrothermal simulations. Freeze-thaw performance indicators are then used to estimate degradation risks, enabling spatial mapping of façade vulnerability.
The methodology is demonstrated on a brick façade in Gothenburg, Sweden, where degradation had been previously documented across 104 façade sections. Two WDR models—ISO 15927-3:2009 and Straube-Burnett (SB)—were applied over a 31-year simulation period. The ISO model at a 75% relative humidity (RH) threshold—used as the criterion for counting freeze-thaw cycles—showed the strongest agreement with observed degradation patterns (PCC = 0.6). The SB model required a higher RH threshold (90%) to achieve moderate agreement (PCC = 0.32). These differences highlight how RH thresholds act as compensating parameters for differences in modeled moisture load rather than direct indicators of critical saturation. Similar correlation levels were obtained with a second brick type, using 85% RH thresholds for both models, indicating that façade microclimate, rather than material properties, dominates the spatial distribution of degradation.
The results show that the proposed methodology can reproduce key spatial patterns of degradation risk without CFD, although the absolute risk quantification remains limited. The methodology offers designers, consultants, and building owners a cost‑efficient basis for prioritizing inspections, maintenance planning, and retrofit strategies by identifying the most microclimate-vulnerable façade sections.