Material Selection Has Significant Environmental Impact - and the Metrics for Evaluating It Have Become More Rigorous
The materials incorporated into a building account for a significant portion of its lifetime environmental impact - both the embodied carbon of production and transportation (the carbon released to manufacture and deliver the material before the building is even occupied) and the operational impact (how the material's performance affects building energy use, indoor air quality, and maintenance). Sustainable material selection requires evaluating materials across multiple environmental dimensions, using published data and third-party certification systems rather than marketing claims. The LEED Materials and Resources (MR) credit category provides a framework for material evaluation that aligns with the ARE PPD's sustainable design content, and that framework reflects the state of practice for environmentally responsible material specification.
Environmental Product Declarations (EPDs)
An Environmental Product Declaration (EPD) is a standardized, third-party verified document that discloses the environmental impacts of a building product across its life cycle. EPDs are based on a Life Cycle Assessment (LCA) that quantifies impacts including: global warming potential (carbon footprint); acidification potential; eutrophication potential; ozone depletion potential; smog formation potential; and primary energy use. EPDs are developed according to product category rules (PCRs) specific to each material type, and are verified by third parties. LEED MR credits for "Building Product Disclosure and Optimization - Environmental Product Declarations" award points when 20 or more permanently installed products from at least five different manufacturers have EPDs.
Recycled Content
Recycled content refers to the proportion of a material that consists of previously used material, either post-consumer recycled content (material that has been through consumer use and been diverted from the waste stream) or pre-consumer recycled content (manufacturing waste diverted from landfill, which is generally less valuable environmentally because the consumer use cycle was not completed). Higher recycled content reduces the demand for virgin raw material extraction and often reduces energy demand for material production. Common high-recycled-content materials: steel (from electric arc furnace production, up to 90%+ recycled content), fly ash concrete (fly ash replaces a portion of Portland cement), recycled content carpet tiles, and glass tile from recycled glass.
Regional Materials
Specifying materials extracted and manufactured within a defined radius of the project site reduces transportation emissions (embodied energy of transportation) and supports regional economies. LEED previously awarded credits for materials sourced within 500 miles of the project; LEED v4's approach uses supply chain disclosure rather than a mileage radius, but the underlying principle remains: materials produced near the project site have lower transportation impact.
Low-Emitting Materials
Building materials and finishes that contain volatile organic compounds (VOCs) - adhesives, sealants, paints, coatings, flooring, composite wood products - release VOCs into the indoor air after installation. VOC exposure is associated with a range of health effects. Low-emitting material requirements specify maximum VOC content levels for these products, typically referencing California Air Resources Board (CARB) ATCM standards for composite wood or South Coast Air Quality Management District (SCAQMD) Rule 1168 for adhesives and sealants. LEED EQ credits for low-emitting materials reward specification of products that meet these standards.
Key Exam Points
- EPD: third-party verified life cycle assessment data; required for LEED MR disclosure credits (20+ products with EPDs).
- Post-consumer recycled content: more valuable than pre-consumer; measures diversion from consumer waste stream.
- Low-emitting materials: limit VOC content in adhesives, sealants, paints, flooring, composite wood.
- Embodied carbon: carbon released in manufacturing and transporting materials; separate from operational carbon.
- LEED MR: disclosure and optimization credits for EPDs, recycled content, responsible sourcing.
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