EMBODIED CARBON IN GREEN RATING SYSTEMS

Background

In 2004, GBI began adopting a Canadian web-based tool developed from the Building Research Establishment Environmental Assessment Method (BREEAM) for US commercial buildings. By the end of 2004, GBI released the Green Globes environmental assessment and rating tool into the US market. Green Globes NC 2019 is based on ANSI/GBI 01-2019 Green Globes Assessment Protocol for Commercial Buildings which is under continuous maintenance and contains six environmental assessment areas under its certification program. These areas are Project Management, Site, Energy, Water Efficiency, Materials, and Indoor Environment. One thousand points are available, of which 150 are in the Materials category. The lowest rating threshold is 35% of all applicable points, which must include at least 20% of the points in each category.

There are multiple sections within the Material environmental assessment area that structural engineers can contribute towards to help achieve program points and address embodied carbon. Table 1 summarizes the sections in Green Globes NC 2019 structural engineers can engage in to help their client reach the target project certification level while reducing the structural system’s embodied carbon.

Credits Related to Embodied Carbon 

Section 5.1.1.1 Whole Building Life Cycle Assessment: To achieve points in Green Globes Section 5.1.1.1, the team conducts a Whole Building Life Cycle Assessment (WBLCA). As part of the WBLCA, structural engineers can run a Life Cycle Analysis (LCA) on their structural framing to measure and reduce the global warming potential (GWP) (See Note 2 under References). A registered design professional must verify the structural material quantities for the design options, with the exception of existing buildings. The final building design shall achieve a minimum 5% reduction for GWP and at least two other impact indicators, with no impact indicator exceeding the baseline building by more than 5%. Early in the design phase, the project team should agree on which consultant should include the WBLCA for the baseline building in their scope. For additional information on developing a baseline building for a WBLCA, see “Whole Building Life Cycle Assessment: Reference Building Structure and Strategies” published by the ASCE SEI Sustainability Committee. Up to 30 points can be awarded to the design team depending on the percentage reduction of adding at least three impact indicators. Table 2 lists the points that would be awarded to the team based on the percentage reduction.

Section 5.2.1.1 Product Life Cycle: This section of Green Globes requires the design team to provide at least 20 Environmental Product Declarations (EPDs) for the project. Depending on the amount and type of EPDs submitted for the project, up to 29 points can be achieved. A majority of structural materials have either a product-specific Type III EPD or industry-wide Type III EPD obtained from the material supplier. By asking structural material manufacturers for product-specific EPDs, structural engineers can drive the market towards transparency regarding the environmental impacts of the materials engineers specify on their projects.

Section 5.2.1.2 Product Life Cycle: This section of Green Globes requires the design team to provide at least 5 cradle-to-grave product-specific Environmental Product Declarations (EPDs) for the project. Depending on the number submitted for the project, up to 10 points can be achieved. It is a benefit not only for the project, but also for the industry since cradle-to-grave product-specific, third-party verified Type III EPDs produce an accurate picture of the environmental effects of a manufacturer’s product. By asking structural material manufacturers for cradle-to-grave product-specific EPDs, structural engineers can drive the market towards transparency regarding the environmental impacts of the materials engineers specify on their projects.

Section 5.4.1.1 Product Sustainability Attributes: In this section, structural engineers can help the project team achieve ten points and reduce the structural system’s embodied carbon by using materials with pre- and post-consumer recycled content, biobased content, or third-party sustainable forestry certification. Some structural materials have optimized the amount of recycled content due to resource availability, manufacturing process, embodied carbon reduction, and consumer demands. For projects utilizing structural timber, engineers can specify a third-party sustainable forestry certification. Green Globes recognizes and accepts the Forest Stewardship Council (FSC), Sustainable Forestry Initiative (SFI), and American Tree Farm System (ATFS) sustainable forestry certifications. Research (see Note 3 under References) has shown timber harvested from responsibly managed forests can contribute to a lower embodied carbon footprint when compared to non-certified wood. Using building products with sustainable attributes can achieve up to ten points for the project.

Sections 5.5.1.1 and 5.5.2.1 Reuse of Existing Structures and Materials: Reuse of existing structural materials on a project both on and off site can help reduce the demand for new materials and the structure’s carbon emissions from extraction and manufacturing. Structural engineers will need to assess and determine the condition and strength of existing structural elements to ensure they will be adequate for the demands of the proposed design. It is paramount that structural engineers are engaged during schematic design when building and material reuse is a design option. Depending on the percentage of the existing structural system that is reused (relative to total square footage of the entire structural system on the project), up to 12 points can be obtained in Section 5.5.1.1. Potentially four points can be achieved for materials on the project that are reused, refurbished, or off-site salvaged. The points for off-site reused materials are based on their value per Section 5.5.2.1.

Section 5.7.1.1 Off-Site Fabrication for Construction Optimization: This section provides the option for project teams to utilize off-site fabricated building elements through modular or prefabricated construction. Structures applying modular or prefabricated construction benefit from shorter site phase programmes, increased worker safety, and reduced material waste and transportational embodied carbon. The quantity of points (up to four) awarded for utilizing modular or prefabricated construction is dependent on the percentage of square footage employing off-site fabrication.

Section 5.7.2.1 Design for Deconstruction (DfD): For a project utilizing design for deconstruction, this section will award the project six points. With select structural systems the upfront costs for designing for deconstruction may be more expensive than traditional construction methods. However, savings can be achieved through reduced assembly construction. A few strategies structural engineers can investigate and employ when designing for deconstruction include using mechanical fasteners over welding, simplifying connections, utilizing standard details to the maximum extent possible, and avoiding cast-in-place concrete composite systems. A structural system designed for deconstruction can provide a renewable construction material resource that can reduce the demand for new materials and promote a circular economy. However, the embodied carbon benefit related to this strategy will not be realized until the materials are reused. For additional guidance and strategies on designing for deconstruction see “Whole Building Life Cycle Assessment: Reference Building Structure and Strategies” published by the ASCE SEI Sustainability Committee.

References
1) Green Building Initiative (GBI). (2019). Green Globes for New Construction (NC) Technical Reference Manual. Accessed June 30, 2021.
https://thegbi.org/files/training_resources/Green_Globes_NC_2019_Technical_Reference_Manual.pdf

2) Carbon dioxide equivalent (CO2-e) is a unit of measurement based on the relative impact of a given greenhouse gas on global warming or its Global Warming Potential (GWP). Therefore, embodied carbon and GWP are often used interchangeably. CO2-e emissions are associated with the extraction and manufacturing of materials and products; in-use maintenance and replacement; and end of life demolition, disassembly and disposal; including transportation relating to all three.

3) See Carbon Leadership Forum. (2020). “Learning about Forests, Carbon, and Wood.” Seattle, WA. Accessed July 10, 2021. https://carbonleadershipforum.org/learning-about-forest-carbon/