Engineered wood products such as cross-laminated timber (CLT) and glue-laminated timber (GLT) are being produced in increasing volumes (Muszynski, Larasatie, Guerrero, Albee & Hansen 2020; Fortune Business Insights 2025). These products are made from renewable but finite resources. During production, defects in sawn timber may be removed, and long lamellas are created by finger jointing the boards. If the raw material could be utilised more efficiently, the resource efficiency of these products would improve.
Standards impose strict limits on the amount of wane allowed in finger joints (FJs), meaning that boards with significant wane—i.e., more than about one percent of the cross-section—are rejected (EN 408, EN 15497, EN 14080). If boards with more wane could be used without reducing the performance of the product, for example in the inner layers of CLT where the stresses are comparatively low, then a greater share of the wood raw material could be used for construction purposes, thus improving the already low carbon footprint of the product. In CLT, stresses tend to redistribute from lamellas with low stiffness to those with higher stiffness. FJs typically have a high stiffness-to-strength ratio, and because of this, approximately 30–50% of initial failures in CLT occur in FJs. Similarly, in GLT, tensile failures often occur in FJs (Olsson & Abdeljaber 2024; Fink, Frangi & Kohler 2014).
While design equations exist for GLT (EN 14080), CLT producers typically rely on resource-intensive European Technical Assessments (ETAs), which may require the destruction of up to 160 m³ of CLT (Brandner, Ringhofer & Sieder 2024). To improve resource efficiency and enable the use of a wider range of raw material, a better understanding of the mechanical behaviour of finger joints—especially those with wane—is needed. This study contributes to that understanding by investigating the relationship between board properties and the tensile strength of finger joints with varying degrees of wane.
Keywords: finger joints, CLT, wane
Authors
Whokko Schirén
Linnaeus University Växjö, Sweden
Anders Olsson
Linnaeus University Växjö, Sweden
Kristoffer Segerholm
Södra Värö, Sweden
Login to download the PDF