“If it can’t be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled, or composted, then it should be restricted, redesigned, or removed from production.”
The Circular Economy
Reduce, reuse, and recycle are still great tips for materials efficiency. The majority of construction products are landfilled (or worse) long before they live out their useful lives, and the carbon emitted to create these materials will continue to exist in the atmosphere for 100 years or longer. Since most embodied carbon comes from raw materials extraction through manufacturing (Life Cycle Analysis stages A1-A3), salvaging materials for reuse is a key way to reduce the embodied carbon of buildings (Post 07).
The circular economy is an economic model where materials and products retain their value through their useful service life, being refurbished or remade into equal or higher quality products after their service life. This is an emerging field; few design teams actively seek reused and refurbished products and few of these products are (currently) available for purchase. However, new systems are being developed to bridge the gap for designers seeking re-use materials. The All for Reuse map includes many of these current efforts; the AIA also developed a guide for Adaptability, Deconstruction, and Reuse.
Just as building-scale embodied carbon analysis begins at the product level with Environmental Product Declarations, building reuse begins at the material and product scales, this post focuses on the circular economy of materials and products while the next one (Post 10) focuses on whole building reuse with an eye toward decarbonization.
Designing for the Dump?
Tenants generally renovate their commercial office spaces about once every 10 years. Trends toward 3 to 5 year commercial office space leases in recent years mean that tenants are leaving behind nearly new materials that often end up in the landfill at the end of their lease so the new tenant starts with an empty shell: walls, floors, ceilings, furniture, fixtures, and equipment. In the hospitality and retail sectors, the churn is happening at an even higher frequency to keep up with market and consumer trends (“finishes ugly out before they wear out”), with retail lease terms as short as 2 years. This churn results in an exponential growth in the waste output from the building industry. An LMN research study estimated that the cumulative embodied carbon from 60 years of cyclical renovations were likely greater than the embodied carbon from the building’s structure and envelope. While some innovative materials are now available (carbon sequestering, reduced manufacturing energy use, or produced using recycled content), focusing only on new products destined for the landfill will not get to net zero carbon.
Most products in the current economic model follow a linear process: raw resources are extracted, manufactured, distributed, used (often briefly), and then sent to a landfill. Even many products advertised or labeled as recyclable like plastics end up disposed in landfills or in the oceans. The next time the same material is needed, more raw resources are extracted, resulting in an accumulation of wasted materials and carbon associated with the materials each cycle.
The industry standard metric for end-of-life material success is waste diversion, referring to the percent (usually by weight) that is kept out of the landfill. Waste diversion, however, includes many things that are not circular:
- 14% of US Municipal solid waste is incinerated, sometimes considered diversion even though it emits carbon stored in the material and pollutes air
- Selling waste to a third party to recycle can be considered diversion even if this material ultimately ends up in a landfill
- Material is sometimes ground up and used as alternative daily cover at landfills or crushed and used as roadways.
Many forms of waste diversion and so-called recycling provide a beneficial second use by downcycling the material. However, the circular economy for materials is based on recycling (resulting in a near-equal quality material as the original) or upcycling materials.
In absolute terms, LEED v4.1 suggests good C+D waste practices are generally less than 10-15 lbs of total waste (including diverted material) per ft2 of building area, which reinforces front-end source reduction.
Organic materials will biodegrade in landfills (included in EPD module C), releasing around 15% of US methane emissions, which are sometimes captured or burned off. Aerobic composting of organics offers a better alternative, producing lower emissions than landfilling. Some ideas around storing biogenic materials long-term are being studied.
In a reuse model, carbon reductions are realized by keeping products and materials in the economy. This requires that products be designed with long-lasting parts, finishes that can be maintained or refurbished, and are easy to be disassembled and repaired. The circular economy goes one step further and includes that each component of a product has an end of life that becomes the raw material for another product.More info