Secondary Timber in Structural Applications: Comparing energy balance of re-use and virgin material

Currently, the cascading use of timber in Europe is minimal, with the majority of material meeting energy recovery after its first use. Secondary timber has typically been through energy intensive processes, such as drying, transportation, and sawing into rectilinear cross sections. This study with focus on structural timber re-use, aims to evaluate whether the invested embodied energy in secondary timber makes it more suited to re-use than incineration from the perspective of energy balance.
A novel I beam concept, with two built prototypes, one from virgin timber, and the other from locally sourced secondary timber provide the case for comparison. The total energy required for each prototype from forest to product and waste stream to product respectively is compared, including the energy fuel value of offcut material as part of the calculation. A key parameter in this study is yield, the effectiveness of a component to utilise feedstock, a factor in which the reclaimed novel beam concept has demonstrated high performance.
The study results suggest that the secondary timbers’ reduced processing demands may lead to an I beam with a lower embodied energy, posing the hypothesis that from an embodied energy aspect, re-used timber offers a more effective material utilisation than components from virgin material. This is further contextualised with other examples of cascading, such as alternative component typologies, exemplifying the important role of design in effectively utilising secondary timber.
In current thinking, secondary timber poses challenges for structural applications. This project’s comparison demonstrate that the savings in energy (waste stream to product) justify the effort of overcoming these. The paper concludes with a discussion of the findings of the study, that have the potential to motivate an increased utilisation of secondary timber in high value, long term applications.