The construction sector accounts for 53.9 % of the waste, about 40 % of the greenhouse gas emissions, and 21.9 % of the raw material consumption in Germany. Hence, it is imperative to decrease waste and emissions while enhancing resource efficiency and the use of renewable resources in the construction sector. The circular economy offers a potential concept to realize these objectives, but innovative technologies and approaches for valorizing demolition waste into high-value secondary products are missing. This paper examines the wood cascading potential of 54 salvaged rafters from building demolition and roof truss deconstruction in southern Germany. The wood moisture content, wood species, and impurities were determined to enhance comprehension of the salvaged rafters’ initial material characteristics. Furthermore, the salvaged rafters were processed into lumber of standardized dimensions. Material losses during each processing step were recorded to calculate the overall material yield and evaluate each processing step's impact in a material flow analysis (MFA). The results show that impurities by fasteners were influenced by the rafters’ installation side, characterized by many close-spaced nails on the upper installation side of the rafters. Screws were less frequently found than nails and staples, but their high breakage rate negatively influences the cascading potential. Attached substances induced challenges in transporting, storing, and processing salvaged rafters. A material yield of 41.9 % resulted from processing salvaged rafters into lumber. Wood warping of the initial rafters was the material characteristic that decreased the material yield the most. Salvaging rafters from demolition or deconstruction has a minor impact on the material yield as long as the rafters are processed into lumber and no reuse is intended. This paper indicates that salvaged rafters can provide a valuable feedstock for valorizing demolition waste wood. By developing new technologies for the industrial and automated removal of impurities, combined with existing wood processing technologies, wood cascading can become an industrial solution for a circular economy in construction. The characterization of salvaged rafters shows that circular-orientated optimizations of structural designs should include detachable fasteners with a low breakage rate, avoidance of cross-section reductions, and wood elements with a low tendency to warp after installation.

As sustainable forestry limits the roundwood supply, wood cascading emerges as a promising concept to meet the growing demand resulting from Germany's transition to a bioeconomy. To assess the environmental impacts of wood cascading resulting from shifting the incineration of recovered wood and the associated substitution of future energy mixes and materials, a consequential life cycle assessment (CLCA) of a wood cascading system providing glued-laminated timber (GLT), particleboard, heat, and electricity is conducted. The assessment of environmental consequences requires a holistic approach, including future-oriented German energy and market scenarios. Furthermore, to analyze the impact of biogenic carbon dynamics, this CLCA was coupled with a dynamic life cycle assessment (DLCA) considering forest growth scenarios and temporal aspects. The results indicate a strong influence of market shifts related to material substitution, followed by energy substitution on the environmental impacts of wood cascading. In fact, the results endorse the implementation of the concept of high-quality wood cascading for substituting non-wood products in Germany, as a transformational path towards a bioeconomy and the achievement of net greenhouse gas neutrality. Compared to the effects of the material and energy substitution scenarios, the forest growth scenarios, which focus on tree species composition influenced by future temperature change and CO2 concentration scenarios, only show a minor influence on global warming impacts. As the findings from applying DLCA contrast with the static approach, it emphasizes the importance of a time-differentiated analysis of biogenic carbon in the evaluation of wood cascading.

Wood auto-fluorescence, primarily attributed to lignin, presents a distinctive feature. Different wood species exhibit variations in lignin distribution. Frequency-Domain Fluorescence Lifetime Imaging Microscopy is effective in distinguishing wood species based on their fluorescence characteristics. This study investigates the potential to differentiate the origins of beech, spruce, and larch through phase-dependent fluorescence decay times. Therefore the zero hypothesis H0 is tested: The phase dependent fluorescence lifetimes of samples from the same species but varying in origin are equal. To determine the fluorescence characteristics of woods of different origins, wood samples of the species Fagus sylvatica L. (beech), Larix decidua Mill. (larch), and Picea abies (L.) H. Karst. (spruce) from Germany, Austria, the Netherlands, Spain, Sweden, New Zealand and Romania were analyzed. The wood samples were analyzed with a FD-FLIM camera setup, including a laser source emitting at an excitation wavelength of 445 nm. Employing Analysis-of-Variance hypothesis testing on fluorescence lifetime data for each wood species, the results indicate that 23 out of 35 origin pairs could be distinguished at a 5% significance level. While acknowledging the challenges of origin-based differentiation, the findings emphasize the promising potential of fluorescence lifetime imaging microscope as a valuable tool in this context. Moving forward, a more intricate approach to sample differentiation should involve acquiring detailed information about the samples, including associated temperature and precipitation profiles, and soil composition.

Whether traditional and emerging innovative wood products and their applications are in fact environmentally friendlier than non-wood products has to be evaluated on a case-by-case basis. Therefore, Life Cycle Assessment (LCA) as a methodological framework to assess environmental impacts of products is introduced and applied to wood and wood-based products. For investigating not only impacts of single product systems but also consequential effects of changing utilization patterns, combining LCA with Material Flow Analysis (MFA) is a useful approach, which also considers shifts of product flows on a regional level. The inherent properties of wood as a bio-based and renewable material, which lead to some specific considerations in the product category rules, are discussed and exemplified by showcasing the main areas of LCA application along the forest-wood value chains. The provision of traceable information about the forest management practices and the chain-of-custody of the wood based materials as important prerequisites for an environmental assessment are discussed. The environmental aspects and implications of wood usage are illustrated for the relevant wood-based products and utilization schemes, from building products to energy use. The contributions of forests and harvested wood products to climate change mitigation are described. Further, examples for the assessment of wood products by resource efficiency and eco-efficiency analysis are presented, and specific focus is given on end-of-life processes and the evaluation of wood cascading options.

Purpose The innovative utilization of hardwood as a future material resource can contribute to a wood-based bioeconomy. Many hardwood-based products are still at the developmental stage, so it is crucial to assess and improve their environmental performance now. Given the lack of knowledge about future conditions, and accounting for potential changes in emerging technologies at an industrial scale, mean that many parameters must be considered. Methods A stepwise approach for prospective LCA has been refined, resulting in two LCA iterations. In the first iteration, a preliminary prospective LCA was conducted to understand the emerging technology, using an uncertainty analysis to identify the most influential parameters. The results were incorporated in the second LCA iteration, the final prospective LCA, to develop future scenarios based on the identified parameters. The approach is applied to three case studies that cover the range of technological readiness levels (TRL) from laboratory to pilot and industrial scale. The first case study is a lignin-based phenol–formaldehyde (LPF) adhesive (TRL 4). The second case study is a hardwood glued-laminated (glulam) load-bearing beam (TRL 7). The third case study is a cellulose-based viscose fiber for clothing (TRL 9). Results and discussion Numerous parameters were narrowed down to a few parameters important for the scenarios; from 25 to 4 in the LPF adhesive case study, from 5 to 2 in the glulam case study, and from 24 parameters to 3 in the viscose fiber case study. The LCIA scenario results for climate change showed differences based on the effects of the important scenario-related parameters, such as the total energy demand or the renewable energy share in foreground and background systems. The LCIA scenario results for land use depend on the amount of wood input and the size of the allocation factor, which was also shown in the local sensitivity analyses. Their variation significantly affected the land use, while having a negligible effect on the other impact categories. Conclusions and recommendations The prospective LCIA results for climate change depend mostly on the energy demand for the manufacture of emerging hardwood-based products. The effects of a high energy demand cannot be compensated for by inputting a higher share of renewable energy production, neither for on-site production nor in the electricity mix. To reduce the climate change impacts, it is crucial to reduce the overall energy demand of the product system. The results for land use are not robust against variations of the allocation factors. Local sensitivity analyses of different allocation methods are recommended. Overall, the inclusion of an uncertainty analysis in the first iteration of the prospective LCA can reduce complexity for the scenario development, especially when the emerging technology to be evaluated presents with a high number of uncertain parameters.

The transition of our economy towards a bioeconomy is likely to increase the demand for wood in the future. Because the roundwood supply is limited, wood cascading is a promising concept for meeting the growing demand. In this context, it is necessary to map the current timber market for analyzing potential options for the cascading of recovered timber, and for quantifying future amounts of recovered timber, differentiated by the type of semi-finished wood product and sectoral origin. Therefore, a material flow analysis (MFA) for Germany during 2019 is performed and a model for the prediction of the recovery of timber volumes (PRecTimber) is developed. This model is based on a distributed decay approach which considers sectoral lifetimes. Historical data for the domestic consumption of timber products are used to calculate the annual decay of various timber products entering consumption. The MFA results in about 62 Mm3 solid wood equivalents (SWE) of various wood raw material assortments being required in the domestic production of wood products. An increasing amount of recovered timber with a minimum of 26.6 Mm3 (13.1 Mt) for 2019 to 29.5 Mm3 (14.2 Mt) in 2050 can be expected. In 2050, the recovered timber is derived from the sectors construction with 52%, furniture with 30%, packaging with 15%, and others with 2% (mainly consisting of sawn wood and particleboard products). The results of the model can be used, to derive estimates of the dimension and quality of the future recovered timber accompanying the potentials for cascading.

The implementation of a circular economy in the construction sector is intended to reduce the environmental impact as well as the construction and demolition (C&D) waste generated. In most life cycle assessment (LCA) studies, the end-of-life (EoL) stage, specifically the demolition stage, is not included because only a marginal influence on the environmental impacts of a building's life cycle is assumed. This study aims to develop a life cycle inventory (LCI) database of the building's demolition stages. By applying the methodology of scientific observation, the demolition processes of five detached and semi-detached buildings located in the south of Germany were attended to record case study specific inventory data, which were then structured in a database. To evaluate the environmental impacts of the demolition stage, a life cycle impact assessment and hotspot analysis were conducted. The main influencing factors of the demolition stage are excavator operation, direct freshwater consumption and related wastewater treatment, as well as container utilization for C&D waste collection and sorting. With a share of 91–95%, excavator operation contributes the most to the impact categories climate change potential, fossil depletion, and freshwater eutrophication. The structure of the database and its user interface allow integration of an LCA calculation into the early design stage and the use of the data for renovation work. The compiled LCI data for the demolition process enables the integration of the demolition stage into the LCAs of a building and allows the calculation of project-specific environmental impacts. Besides, the LCI data is important for conducting environmental product declarations, since the EoL stage is mandatory according to the international standard DIN EN 15804.

To establish a bioeconomy, the demand for renewable resources like wood is likely to increase. To satisfy the demand, cascading, i.e. the sequential use of one unit of a resource in multiple applications with energy recovery as the final step, is a key concept to improve the efficiency of wood utilization. Today, the systematic wood cascading is still in its infancies and limited to the downcycling of wood, i.e. the degradation of material quality. New recycling technologies are needed, which maintain the material quality at the beginning of the cascade chain and mobilize yet unused resources. Therefore, a new recycling technology for recovered solid wood from construction into glued laminated timber products was developed.1 To identify the environmental and economic performance of the process, the eco-efficiency was assessed by the joint application of life cycle assessment (LCA) and life cycle costing (LCC). As reference system, the incineration of the recovered wood was analyzed, representing the common treatment for recovered wood from construction in Germany. System expansion was applied to solve multifunctionality. The results indicate that the recycling of recovered wood into glued laminated timber products is environmentally and economically viable and offers possibility for the production of value added products. The recycling further shows up to 29% of lower environmental impacts and 32% of lower costs compared to the incineration, if system expansion is based on wood energy. The operational processes required for the solid wood cascading are of minor relevance for the economic and environmental performance. Instead, primary technologies like glue lamination and the incineration are key drivers. In all considered scenarios, the material recycling has a 15-150% higher eco-efficiency compared to the incineration. In conclusion, the further development for the practical implementation of the recycling process is recommended to enhance the implementation of the cascading concept.

Driven by the scarcity of non-renewable resources and a growing environmental awareness in Germany, the demand for wood could likely exceed its sustainable supply within the next decades. In response to this development, cascading, i. e. the sequential use of one unit of material in material applications with energy generation as final step, is expected to enhance the resource efficiency of wood utilization. In this context, the objective of this paper is to determine the resource consumption and resource efficiency of wood cascading compared to the use of primary wood to provide the same multiple functions. To account for resource use and calculate the efficiency, exergy analysis was applied. The exergy of a material is the potential work that can be obtained from the material in the natural environment. By using Exergy Flow Analysis, key drivers of exergy dissipation and thus hotspots for improvement were identified. Exergetic Life Cycle Assessment was applied to determine resource use and the resource efficiency at a life cycle level. The results indicate that cascading leads to less resource consumption compared to the use of primary wood, indicated by higher resource efficiency (46% vs. 21%) at life cycle level. The main resource saving potential through cascading arises from avoiding primary production in forestry systems. In conclusion, cascading reduces the primary resource extraction and makes wood utilization highly efficient. Exergy analysis proved to be a viable method to study the resource use of multifunctional cascading systems, although showing some limitations with respect to land use accounting.

In future, the demand for wood will exceed the supply. Thus, the concept of cascading is expected to increase the efficiency of wood utilization. The presented research approach deals with the environmental and economic assessment of wood cascading using Life Cycle Assessment methodology.