The durability of timber buildings: a decay prediction model to estimate the life expectancy of timber structures

The aim of this research work is to develop reliable strategies to assess the durability of timber structures investigating the natural hazards affecting the safety and the life-expectancy of timber buildings. From an all encompassing point of view, the life-expectancy of timber buildings was predicted considering the effects of a fungal attack on the durability of a timber structural element. The prediction of life-expectancy of timber buildings was set up through a risk-based approach consisting of (i) the analysis of the state of the art, (ii) the definition of risk classes and decision trees, (iii) the prediction of the decay. This approach was used for the structural elements of all critical points of a timber building (i.e.: the wall-foundation connections, the balconies, the openings, the wall and floor, and the roof). The analysis of the state of the art allowed to define the decision trees that address all the possible scenarios where water can intrude within the construction details that most affect the durability. Based on a thorough review of the major European standards addressing timber “use-classes”, five risk classes were defined associating the potential hazards to the possible moisture content. The decision trees can associate one of these risk classes to a detail under analysis providing a straightforward indication about the exposure of a timber structural element to decay due to fungal attack. The allocation to a risk class allows to evaluate the leading parameters of a decay prediction model based on suitable functions available in the literature. This procedure can apply directly to the design process of a timber building, while inspection procedures were defined to support the assessment of existing timber buildings. Selected case studies were analysed to compare the results of the risk-based procedure to the outcomes of the inspections. Eventually, a procedure updating of the decay prediction model based on experimental evidence is introduced, together with a software still under development named TSafe that facilitates the application of the methodology by the stakeholders involved in the project.