A method of detecting whether the delignification of tile battens is a structural defect

Abstract

Delignification is the gradual degradation of the natural adhesive (lignin) between wood fibres. Despite its prevalence in (usually older) timber roof battens supporting terracotta roof tiles, limited research exists on its impact on the long-term structural performance of timber roof members. In this study, over 120 karri tile battens with a range of extents of delignification were sampled from three tiled roofs in Perth, Western Australia, in 2023. They were tested in minor axis bending using the test methods in AS/NZS 4063.1. The bending strength and Modulus of Elasticity were compared with the extent of delignification. The results indicated that the extent of delignification had no effect on the mechanical properties of the residual cross-section of timber in the battens. Moreover, the delignified batten strengths were consistent with a linear relationship between the fibre strength and age in service extending beyond 50 years. A method was proposed for assessing fitness for purpose based on only the age of the batten and the cross-sectional dimensions of the sound timber remaining under the delignified material.