Cascading potential of salvaged rafters from building demolition and deconstruction in southern Germany

Abstract

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. • Processing salvaged rafters into lumber results in a material yield of 41.9 % • Warping of salvaged rafters has a major impact on material loss during processing • Cascading potential for salvaged rafters is unaffected by the demolition method • Frequency of fastener holes in lumber depends on the rafter’s installation side • Screws show the highest breakage rate and influence wood cascading negatively

Topics & Concepts