End-of-Life and Reusing Mass Timber

Amanda Stanton M.S. Terminal Project:

Reusing Mass Timber: An Investigation of the Opportunities and Challenges

The exploration of the end-of-life of mass timber materials has little information. As mass timber buildings become increasingly constructed and used, the question of what will happen to the products at the end-of-life of the building comes into question. Currently, the United States averages at 25-50 years for a commercial building and 50-100 years for residential buildings. This is partially due to the ease of retrofitting and the timber materials used in residential construction. If this lifespan of buildings continues with mass timber, the potential for reuse needs to be address.

Mass timber has minimum end-of-life scenarios. In many cases the panels are disposed in the landfill due to the adhesives that are used in manufacturing the material. Recycling to biofuel and incinerating for bioenergy have come into play, however, the adhesives and chemicals create barriers for these disposal methods. Another option is reprocessing and reusing the material. Many mass timber products could have the opportunity to be dismantled from old construction, cleaned, reprocessed, and reconstructed into new structure. This would allow the carbon sequestration of the mass timber products to continue and reduce the carbon impact the product may have if disposed of in a landfill to decompose and release carbon dioxide and methane. However, a series of challenges must be taken into consideration when considering reuse. My thesis looks at creating a guideline to address challenges and opportunities when considering reuse and applying it to a design project.

Multiple types of mass timber products could be reused. A couple cases with CLT have already been explored. The main focus of my research will be looking at veneer products, such as MPP (Mass Plywood Panels). The advantage of the MPP is its capability to span 2 directions and be cut down to act as panels, beams, and columns.

The main focus of the research is to look at keeping the timber products as structural members, mainly primary structure that continues to support loads. This is mainly focused on upcycling the product into beams, columns, or smaller panels when considering taking existing panels and reusing them. Downcycling must also be considered for panels that may face damage that leaves them structurally insufficient to be reused at a gravity-loaded system. Downcycling can also prevent the panels from being placed in the landfill by using the product to create furniture, wood particle products, and other non-structural objects.

Challenges throughout this process must be considered. The reused panel may initially face damage from its previous life with seismic activity, loads, damage from deconstruction, hidden defects not visible to the eye, reprocessing to cut connections and defects off, proper storage based on the materials to prevent delamination and other loss of structural integrity, transportation, and the new design being influenced by the reprocessed material’s sizes and capabilities.

A case study that has explored reusing CLT is the CLT Cafe in Kobe City, Japan designed by Utsumi Aya Architects and studied by Rafael Passarelli. The project used the 5th-story of a shake table test, where no visible damage was noticed, and downcycled the panels from primary structural use to a secondary structure of the roof system at the CLT Cafe.

Another case study that utilizes reused 3-ply CLT panel is the Salvage Swings Pavilion by Somewhere Studio. The pavilion was created with reused 3-ply CLT pallets that were reprocessed and cut into smaller panels to form the box-like sections of the Salvage Swings Pavilion.

Moving forward, the exploration of this study is to look into the minimally explored area of the end-of-life of mass timber. The outcome is to create a guideline to address the opportunities and challenges of reusing mass timber in the industry. The focus of the study needs to include all aspects of reuse and the processes needed to accomplish reusing mass timber with minimal waste. This will require investigating disassembly, planning for deconstruction as the main focus, reprocessing, storage, transportation, and the requirements for reconstruction.