Stochastic Approach to the Factor Method: Durability of Rendered Facades

The degradation of building materials occurs as a stochastic phenomenon. Service life prediction methods are usually divided into deterministic, stochastic, and engineering methods. Deterministic models are simpler and easier to use, but are unable to capture the random nature of the degradation phenomena. On the other hand, stochastic models are more complex but very efficient in dealing with the uncertainty associated with a building's performance. In this study, a stochastic approach to the factor method is proposed to predict the service life of rendered facades. The model proposed is based on a survey of the degradation state of 85 rendered facades located in Portugal. The factors that affect the durability of this type of coating are identified and translated into probability distributions. This analysis leads to coherent values, revealing that facades on buildings built with adequate design measures are more durable; facades exposed to adverse environmental conditions are more prone to degradation and are penalized in the quantification of durability factors; private buildings are more prone to suffer degradation (this result is related to the budget available for maintenance). This methodology provides an estimated service life of any given rendered facade through a probability distribution. (C) 2015 American Society of Civil Engineers.