PSI - Issue 81

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

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Another cause of moisture penetration into timber roof elements is condensation. This phenomenon occurs particularly often in cold roofs. Moisture of this type is also local in nature, affecting only the upper part of rafters that come into contact with the waterproofing membrane (Fig.2). Visually, this defect appears as a change in the colour of the upper portion of the rafter. Under normal ventilation conditions, no decay was observed at any service life when condensation was the only moisture source. Thus, with proper roof ventilation, this defect does not pose a risk to the structural condition of the rafters. a) b) c)

Fig. 2. Influence of condensation moisture 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

It is important to note that the impact of condensation moisture increases sharply when the attic ventilation regime is inadequate. In such cases, mould and mildew develop rapidly on dampened rafters, followed by timber decay. This process is so rapid that decay was observed even in rafters with a service life of less than 10 years (Fig.3). Such rafters were found to be unfit for continued operation and required replacement. At the same time, during the study, there were roofs with significantly longer service lives (50 – 100 years) where no decay was detected, despite considerable age. All these roofs had proper ventilation. Therefore, appropriate ventilation can be considered a key factor in ensuring the durability of timber structural elements. a) b) c)

Fig. 3. Adverse effects of condensation moisture combined with inadequate ventilation (a, b, c)

One of the most widespread defects identified during the study was the presence of longitudinal cracks in timber elements of the rafter system (Fig.4). These cracks formed due to variations in temperature and humidity conditions during service, as well as non-compliance with prescribed moisture content requirements for timber used in construction. It should be noted that the size of cracks in older timber elements was generally greater than in newer elements. a) b) c)

Fig. 4. Longitudinal cracking in timber roof elements: a) service life up to 10 years; b) service life from 10 to 50 years; c) service life over 50 years

Another defect identified was infestation of timber by wood-boring insects (Fig.5). Notably, there was no direct correlation between the service life of timber elements and the frequency of this defect. The likelihood of infestation depended on whether bark residues were present on the timber and whether proper antiseptic treatment had been applied. In roofs with a service life of up to 10 years, this defect was not detected. Furthermore, the extent of infestation did not correlate with the age of the timber: as seen in Fig. 5, the infestation on roofs with a service life of 10 – 50 years was significantly more extensive than on some roofs aged 50 – 100 years.