The construction industry creates significant volumes of waste timber, much of which has residual quality and value that dissipates in conventional waste management. This research explored the novel concept of reusing secondary timber as feedstock for cross-laminated timber (CLT). If cross-laminated secondary timber (CLST) can replace conventional CLT, structural steel and reinforced concrete in some applications, this constitutes upcycling to displace materials of greater environmental impacts. The fabrication process and mechanical properties of CLST were tested in small-scale laboratory experiments, which showed no significant difference between the compression stiffness and strength of CLST and a control. Finite element modelling suggested that typical minor defects in secondary timber have only a small effect on CLST panel stiffness in compression and bending. Mechanically Jointed Beams Theory calculations to examine the potential impacts of secondary timber ageing on CLST panels found that this has little effect on compression stiffness if only the crosswise lamellae are replaced. Since use of secondary timber to make CLST has a more significant effect on bending stiffness, effective combinations of primary and secondary timber and their appropriate structural applications are proposed. The article concludes with open research questions to advance this concept towards commercial application.

<p>New York is known as a metropolis of skyscrapers; however less than 1.5% of the 1 million buildings in the city stand over seven stories tall. Over 95% are thought to be of wood-frame or masonry and wood construction.</p><p>Most of this building stock was constructed using wood sourced from old-growth forests across the eastern seaboard. The city now sits on a stockpile of wood which germinated before New Amsterdam became New York, and which was felled while signatories of the Declaration of Independence were still President; this is structurally valuable hard, dense and high strength-to-weight ratio wood. As our buildings degrade and require renovation or replacement the city must ensure that this resource is not wasted, for environmental and economic reasons.</p><p>The total number of buildings is large, but because of the rapid and repetitive way that NYC was constructed the variation in building type and structural element sizes across the building population is small. Cross referencing NYC department databases using geographic information systems allowed the Department of Buildings to produce an estimate of the number of buildings in the city of each type. Assessment of historic pattern books, prescriptive regulations, and inspection of existing buildings allows generic estimates of wood dimension and quantity per building type. Combined, this data allows the estimation of the annual rate of release of wood from demolition in NYC - a predicted supply available for future use. A review of existing practices in wood salvage, processing and reuse is then assessed in context, outlining proposals for future local policy and research work.</p>

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