PSI - Issue 81

Andrii Pavluk et al. / Procedia Structural Integrity 81 (2026) 198–204

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maintenance practices (Gomon et al. (2024); Green and Kretschmann (1992); Pavluk et al. (2024); Galicki and Czech (2005); Homon et al. (2025)). Inspection experience shows that, under proper maintenance, the service life of timber roof elements can significantly exceed the design service life specified in national building codes. Conversely, in cases of inadequate roof maintenance, the service life of timber rafter systems may be drastically reduced. Therefore, the present study is highly relevant. The aim of this research is to identify the most common defects and damages observed in timber structures of in-service roofs. 2. Methods of research According to current Ukrainian building standards (DSTU, 2024), the most common defects in timber roof structures include: • Moist or periodically wetted timber; • Changes in the natural colour of the timber; • Unacceptable deformations of structural elements; • Damage caused by wood -boring insects; • Technological (manufacturing or installation) defects; • Shrinkage -induced cracking; • Timber decay (rot); • Corrosion of metal components at structural joints; The investigation of timber structures was conducted on in-service roofs with various structural configurations, cross-sectional dimensions of timber elements, and different service lives. In total, fifty existing roofs were examined. For analytical purposes, these roofs were conditionally divided into three groups based on their service life: Type I – up to 10 years; The defects and damages listed above were identified in the load-bearing timber components of the roofs. Additionally, the causes of defects, their impact on the technical condition of the elements, and their frequency of occurrence were analysed. The identification of damage in timber structures (Blass et al., 2011; Kanal et al ., 2017; Magnière et al., 2014; Mergny et al., 2016; Pa Sun, 2022) and the assessment of its occurrence frequency were carried out in accordance with existing methodological approaches (Palma et al. (2020); Ross et al. (1999); Zheng et al. (2020); Yang et al. (2020); Blass et al. (2010)) as well as relevant building standards (Eurocode 2, 2004; DBN, 2017). The inspection was performed visually, supplemented by instrumental measurements of the cross-sections of timber elements and the dimensions of the detected defects. The extent and volume of identified defects and damages were also recorded. 3. Results and discussion Each of the defects and damages listed above was identified on the examined roofs; however, the causes of their occurrence and the patterns of their development exhibited certain specific features. One of the most common defects observed was leakage of the roofing layer, which led to systematic wetting of timber structural elements. Over time, in the absence of timely repairs and proper maintenance, decay processes would begin to develop in these areas. Fig.1 shows the condition of timber elements subjected to prolonged moisture exposure for all three roof types with different service lives. a) b) c) • Lack of protective surface treatments; • Charring (resulting from fire exposure ). Type II – from 10 to 50 years; Type III – from 50 to 100 years.

Fig. 1. Influence of moisture and periodic wetting on timber roof elements: a) service life up to 10 years; b) service life from 10 to 50 years; c) service life over 50 years

As illustrated, the longer the timber is exposed to moisture, the more severe the detrimental effect on the material. No decay was detected in roofs with a service life of up to 10 years. However, on several roofs older than 10 years, timber decay was recorded. The extent of decay was directly dependent on the amount of moisture, and therefore on the size of the leakage area. Typically, such areas were small and localised.