Wood is a renewable resource and a promising construction material for the growing bio-based economy. Efficiently utilising wood in the built environment requires a comprehensive understanding of the dynamics regarding its usability. Durability is an essential property to consider, as various types of exposure create conditions for the deterioration of wood through biotic and abiotic agents. Biodegradable materials introduce increased complexity to construction and design processes, as material decomposition during a structure’s lifetime presents a physical risk to human health and safety and costs related to repairs and maintenance. Construction professionals are thus tasked with utilising wooden elements to accentuate the material’s beneficial properties while reducing the risk of in-service decomposition. In this paper, only the cause and effect of fungal induced decay on the service life of wooden buildings and other wood-based construction assets are reviewed. The service life of wood components can thus be extended if suitable growing conditions are controlled. Multiple existing modelling approaches are described throughout the text, with special attention given to the two most comprehensive ones; TimberLife and the WoodExter. In choosing an appropriate model for a specific application, the authors recommend evaluating the model’s regional specificity, complexity, practicality, longevity and adaptability.

In performance-based durability design, relating the in-use conditions of wooden members to their moisture content is an important step. In the present study, the effects of detail design on the wood moisture content of glulam members are investigated experimentally. The moisture content of glulam members, designed with various connection details and structural protection, was monitored at 18 different measuring points (n = 3) by use of resistance-type moisture sensors for a period of a year. The effects of detail design are studied by comparing the moisture content of various details to that of a freely exposed beam. As expected, the design of the details was clearly reflected by their moisture content. Efforts to protect the wood were favourable in most cases, although only complete shelter kept the moisture content consistently below the level critical for the occurrence of decay. In order to relate the effects of moisture traps to the climate, a three-parameter empirical model was constructed and fitted to the experimental results. The model was able to capture the main features of the measurements and was used in order to characterize the performance of details in terms of their response to weather.

Construction using timber has seen a resurgence in light of global climate mitigation policies. Wood is a renewable resource, and engineered wood products are proving to be competitive against concrete and steel while having several advantages. However, while the renewable nature of wood in construction is a beneficial property for climate mitigation policies, the process of biodegradation introduces a challenge for service life planning. A review of hazard mapping is presented while developing contemporary hazard maps, occurrence maps and projected hazard maps for 2050 using representative concentration pathways (RCP) 2.6 and 8.5. The risk of timber decay is expected to increase in most of Europe as the temperatures rise, with a decrease expected in dryer regions. Termites are likely to experience a range expansion as more areas become suitable, while human activity and an increase in extreme weather events like floods are expected to facilitate dispersion. Marine borer species already present a risk in most European coastal regions; however, the effect of changes in water temperatures are likely to shift the boundaries for individual borer species. Overall, warmer climates are expected to increase the metabolic activity of all of these organisms leading to a general reduction in service life.

The effects of weathering on the in-service moisture behavior of wood have received only limited attention so far, with much focus being on the effect of photodegradation on the hydrophobicity of the wood surface. The objective of the present study was to examine the effect of weathering surfaces on the overall moisture behavior of wood specimens exposed to short-term cyclic spraying, with special emphasis on the surface conditions involved. Specimens cut from eight different species including hardwoods and softwoods were weathered for 8 years and continuously monitored during a single-sided cyclic spraying together with a set of axially matched controls. After each spray cycle, the duration of surface wetness was evaluated by resistance moisture sensors as well as an optical approach (colorimetric) based on time-lapse images. The moisture content in the core was monitored simultaneously by use of resistance moisture sensors. The optical method correlated well with the electrical resistance measurements and provided a simple and practical measure of the areal distribution of the surface wetness. The results showed specimens with a weathered surface to sustain a wet surface for about twice the duration of their axially matched control. A considerable, albeit smaller, effect was also observed deeper in the core. By adapting the length of the wet period on the exposed boundary, the corresponding response at the core of the Norway spruce specimens was reproduced numerically.

Joints in timber structures are particularly vulnerable to degradation due to their tendency to trap moisture. The mechanisms involved, and their effect on the moisture conditions of wood, are here investigated numerically. The horizontal member of a rail and post-type configuration is modelled numerically by a two-dimensional diffusion model with material properties for Norway spruce. Contact areas are assumed to be fully wetted when the specimen is exposed to free water but are unable to interact with the ambient air. Water that is absorbed through such areas cannot dry out through the same surface and is instead redistributed. The model was validated against experimental data, both previously unpublished data and data obtained from the literature, including both laboratory and outdoor exposure. The numerical solutions were, in general, consistent with the measured data. The model provides a simple, yet accurate, method to estimate the moisture conditions in certain types of wood joints. In addition, the spatial distribution of time spent above 25% moisture content was calculated, in order to investigate the suitability of the model for durability applications.