Buildings have an impact on people and the environment throughout their entire lifecycle, starting with extracting resources from the earth to putting them back in the earth, or burning them, at the end of their lives. To evaluate the effect of buildings in this regard, everything from the energy they consume, the waste they generate, and the carbon dioxide (CO₂) they emit must be considered throughout the six major cycles below.
The combination of wood and the Passive House standard is a common-sense approach that can have a very positive lifecycle impact on the environment. In fact, according to a report from the U.S. Forest Service, wood in building products yields fewer greenhouse gases (GHG) than other common materials.*
1. Resource extraction
Everything in buildings comes from natural resources, some of which grow relatively quickly above the ground (e.g. wood), while others take millions of years to form below the ground (e.g. materials derived from fossil fuels). Taking a look at wood, the amount of heat, water, and pollution generated compared to extracting iron to produce steel, or extracting limestone to produce cement is significantly lower.**
The lifecycle of wood has a smaller impact. For example, the sun hits the tree, and the tree grows. It can be cut down with light machinery and a new tree is planted. It absorbs carbon, provides oxygen, and can be used in the future. In this context, it means a more sustainable production, compared to making concrete or steel, where digging for oil, coal, or natural gas and then burning it is a prerequisite to extracting the raw materials from the earth.
The real ‘weight’ of a material—including resources, water, and energy used at the entry point of a manufacturing facility—compared to the material that comes out at the other end is referred to as the ‘ecological backpack.’ This measures the environmental impact of manufacturing products. Common sense suggests it requires less resources and energy to manufacture wood products compared to concrete and steel. Heavy timber and mass timber products can meet the same structural and fire requirements that also govern concrete and steel.
3. Off-site and onsite production
In many cases, the process of constructing buildings is antiquated, relying on manual and labor-intensive onsite processes. Other fields, such as manufacturing automobiles, have advanced considerably using automation and an industrialized system approach to designing and building, where the energy efficiency, in miles per gallon, can be guaranteed and the assembly occurs in a modern factory. Modern wood prefabrication processes can offer new opportunities and better working conditions. In this respect, building with wood can offer fast and efficient options for construction.
The natural resources needed to produce and deliver the energy consumed to heat and cool buildings for lighting, appliances, and water is the highest of all six lifecycle steps. While more efficient lighting and appliances can be specified, the only way to reduce long-term heating and cooling loads is to improve the building envelope. Airtightness is the most important element that has made the Passive House standard succeed. It can easily be achieved using modern wood carpentry, as discussed in this article.
At the end of a building’s lifecycle, products are usually disposed of in landfills. Using a system approach to construction, buildings can be designed so they can be disassembled and separated for recycling. Design optimization, use of recovered wood, and specifying jobsite waste to be separated and taken to a local recovery center are all ways to reduce, reuse, and recycle.
Wood from buildings can be recovered for use in other buildings or be employed to create furniture or other products. Even at the end of their second or third ‘life,’ wood products can be burned to generate energy or decompose naturally in the earth.
*See USDA Forest Service’s “Science Supporting the Economic and Environmental Benefits of Using Wood and Wood products in Green Building Construction.”
** For more, see the International Journal of Life Cycle Assessment article, “Wooden Building Products in Comparative LCA: A Literature Review,” by Frank Werner and Klaus Richter. Visit www.vhn.org/pdf/LCA-Wood-algemeen.pdf.
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