This book introduces a maintenance model that will assist decision-makers in their choice of building maintenance policies.   The model is stochastic and condition-based that analyses the impact of different maintenance strategies on the durability and performance of different buildings envelope elements (facades, windows, and roofs).  As non-structural elements, the maintenance of buildings envelope can be disregarded stakeholders. However, as first barrier to the external environment, these elements are critical to buildings' overall performance and are expected to meet aesthetic, comfort, safety, and durability requirements. The methodology presented is innovative. The maintenance model is based on a Petri net formalism and includes degradation, inspection, maintenance, and renewal processes. The model provides key information, such as: i) the impact of different maintenance strategies on the service life and durability of the building components; ii) the impact of maintenance on their performance over time; iii) the life cycle costs; and iv) the impact of maintenance on the buildings' use.   The book will be of use to a variety of professionals in the construction sector.