The first Shikinen Sengu was held in the year 690, in the city of Ise, Mie Prefecture, Japan. It consists of a set of ceremonies lasting up to 8 years, beginning with the ritual of cutting down trees for the construction of the new Ise Shrine and concluding with the moving of the sacred mirror (a symbol of Amaterasu-Omikami) to the new shrine by Jingu priests. Every 20 years, a new divine palace with exactly the same dimensions as the current one is built on a lot adjacent to the main sanctuary. Shikinen Sengu is linked to the Shinto belief in the periodic death and renewal of the universe, while being a way of passing on the ancient wood construction techniques from generation to generation.
The idea of creating a building that will have an expiration date is not a common one. In fact, the useful life of a structure is often given little consideration. When demolished, where will the materials go? Will they be disposed of in landfills or could they be reused in new projects? There are certain construction methods and materials that make this process easier. Others make reuse unfeasible, due to several factors.
The so-called Design for Deconstruction (known by the acronym DfD, or Design for Disassembly) considers how all decisions made in the design phase can increase the chances of reusing the building parts at the end of their useful life. As defined in the EPA (United States Environmental Protection Agency) manual, “the ultimate goal of the Design for Deconstruction (DfD) movement is to responsibly manage end-of-life building materials to minimize the consumption of raw materials. By capturing materials removed during the renovation or demolition of buildings and finding ways to reuse them in another building project or recycle them into a new product, the overall environmental impact of end-of-life building materials can be reduced. Architects and engineers can contribute to this movement by designing buildings that facilitate adaptation and renovation. Designing for Deconstruction is designing so that these resources can be economically recovered and reused.” Taking the example of Canada, buildings are the largest consumers of raw materials and energy and the biggest contributors to the waste stream by weight, which equates to 3.4 million tons of building materials sent to landfills annually, representing an estimated 1.8 million tons of incorporated carbon.
An even broader concept is that of DfD/A, or Design for Disassembly and Adaptability. It is a strategy that also seeks to extend the life cycle of buildings and their components, allowing the building to be updated, maintained, and modified more easily; but, at the end of its useful life, disassembly still allows for the more efficient collection and reuse of materials and components. Managing the return and recovery of products and materials from companies, demolition sites, and material recovery facilities back into the value chain is the role of reverse logistics, a fundamental principle of the circular economy that allows product materials to be recycled, reused, and remanufactured.
Such concepts contrast with the linear model, which is focused on extraction, use, and disposal of materials in landfills or even irregular dumping. DfD/A attempts to avoid this exploitative system, ensuring that after dismantling, the materials have a known and well-considered destination. This can generate a number of benefits, including reducing waste and greenhouse gas emissions in buildings; improving the resilience of supply chains in construction; creating new economic, and employment opportunities, providing social benefits, and improving natural ecosystems through lower resource consumption.
The theoretical model works very well. But in practice, things are much more complex. Demolitions are usually carried out quickly, making it impossible to reuse a large part of the materials. First, it is essential to address the proper disassembly and separation of the parts that make up the building. But it is also essential that the project, from the beginning, seeks methods and solutions that reduce or eliminate waste, including products that are easily detached and disassembled as well as good quality materials that allow reuse and avoid harmful and polluting chemicals.
But the decision to choose a material or construction system, naturally, will not depend only on the requirements of disassembly. To aid in this selection, the life cycle assessment, widely discussed in this article, is a common method that helps shed light on the impacts of a product or process, from the beginning of the process (extraction of raw material) to the end of the process (reuse, recycling, or disposal).
According to the Circular Economy & the Built Environment Sector in Canada, using wood products—specifically mass timber (glue-laminated timber, cross-laminated timber, etc.)—can reduce the building's carbon footprint in several ways:
First, wood is a renewable resource and its growth takes place through photosynthesis and not through mining or extraction. Trees grow in almost all climates, and using local species can greatly reduce the amount of energy expended on transport. When a tree is harvested to make lumber and engineered wood, it stores carbon in the building. When another tree is planted in its place, it will also absorb and store carbon. Last but not least, because wood is versatile and durable, it can be disassembled and then reassembled into other buildings or other wood fiber products, sequestering the carbon even longer as long as it stays out of landfills. Even if it doesn't have a construction use, wood can be turned into various valuable bio-based products, such as biochar, which can replace coal and also be used as an agricultural fertilizer.
A report by Delphi Group and Scius Advisory also points out that, together with greater awareness of building materials and their impacts, growing trends in digital technologies have allowed for a circular economy in the built environment through greater productivity, efficiency, process improvements, and enhanced collaboration. Examples include BIM software, virtual reality (VR), drone technologies and new digital tools that improve tracking of material flows.
The junction between technology and ancient techniques, between recently created concepts and observations of nature, seem to be the best way to a sustainable future and a reconciliation with nature, of which human beings are a part and in which we are active agents of change. This includes understanding the materials and processes that make up the entire life of the construction, which will help us make more coherent and correct decisions guided by sustainability and responsible design.
Learn more about the Circular Economy and the Built Environment Sector in Canada in this report.