Service life prediction of exterior cladding components under failure conditions

The reliability of service life prediction of building components strongly affects the effectiveness of maintenance policy setting. Despite continuous research and development efforts, existing methods still suffer lack of robustness. Typical failure mechanisms in exterior cladding systems, deterioration patterns, and service life limiting coefficients (modifying factors) are identified for a range of failure mechanisms. The method is based on monitoring the physical and visual performance of building components under similar service conditions, at different periods in the building service life. Three types of exterior cladding are studied: cementitious mortar, synthetic rendering, and ceramic mosaic. Failure mechanisms identified include: lack of design details (such as drip-edge and expansion joints), faulty design under marine environment, exposure to air pollution, and poor workmanship. Three typical deterioration patterns under failure conditions were determined statistically, namely, linear, exponential and logarithmic. The proposed method addresses two issues raised in ISO-15686 in order to improve the precision and reliability of service life forecasting: (a) modifying factors for quantifying the effect of failure mechanisms are estimated within 80% confidence limits and (b) the prediction models yield high degrees of fit to the data (coefficient of determination values ranging between R2 = 0.88 and R2 =0.96 at a 0.0001 level of significance).