EMBODIED CARBON IN GREEN RATING SYSTEMS

Energy + Carbon Reduction:

This core imperative requires that new or existing buildings demonstrate a 20% reduction in the embodied carbon of primary materials when compared to an equivalent baseline. Embodied carbon measurements for the baseline and project should be based on stages A1 (Raw material extraction) – A5 (construction installation) as defined by standard EN 15978. Measurements for embodied carbon should be completed using an approved Whole Building Life-Cycle Assessment (WBLCA) tool. Some WBLCA tools approved by ILFI include Tally, Athena Impact Estimator, and One-Click LCA. The project’s baseline should be identical to the initial design except for the claimed material reductions, similar in project scope, and use material and design parameters based on standard industry practices. Additional information on establishing a baseline can be found in the Energy Petal Handbook, version 4.0 from ILFI. Existing buildings may count as in-situ materials against the required 20%. As part of the WBLCA, structural engineers can run a Life Cycle Analysis (LCA) on their structural framing. An LCA and understanding of materials’ embodied carbon can highlight high carbon impact areas and allow the structural engineer to actively provide solutions to meet the 20% reduction from the baseline. Early in the design phase, the design team should agree on which consultant should include the WBLCA for the baseline in their scope. By measuring and utilizing reduction strategies, structural engineers can reduce the building’s embodied carbon footprint to the greatest extent possible.

Net Positive Carbon:

For buildings to meet this imperative, projects must account for the embodied carbon emissions by utilizing carbon-sequestering materials and/or a one-time carbon offset purchase through an ILFI approved carbon offset provider. Embodied carbon measurements that are offset should be based on stages A1 – A5. Measurements for embodied carbon should be completed using an approved WBLCA tool. Approved ILFI WBLCA tools include Tally, Athena Impact Estimator, and One-Click LCA. Through the WBLCA, engineers can reduce the structural system’s embodied carbon to the greatest extent possible and account for the carbon-sequestering materials, such as wood. The larger the reduction and more carbon-sequestering materials used architecturally and structurally, the fewer carbon offsets the owner has to purchase.

Responsible Materials and Imperative 14: Responsible Sourcing:

This imperative requires:

1) One Declare label per 2150 square feet (200 square meters), for up to 20 distinct products. All other product manufacturers must, at a minimum, receive a letter requesting the manufacturer disclose their ingredients and identify any Red List content.

3) 50% of timber used on the project to be Forest Stewardship Council (FSC) certified, salvaged, or harvested on-site either for the purpose of clearing the area for construction or to restore or maintain the continued ecological function of the site.

4) 20% or more of material’s construction budget originates within 310 miles (500 kilometers) of the project site. See the ILFI CORE Standard for the definition of the materials construction budget. 

5) The project must divert 80% of construction waste from landfills.

Therefore, structural engineers will need to update their specifications to convey these requirements to the contractor. Research has shown that timber harvested from responsibly managed forests, like FSC Certified wood, can contribute to a lower embodied carbon footprint than non-certified timber.

Net Positive Waste:

Net Positive Waste strives to have projects reduce or eliminate the production waste during design, construction, operation, and end of life. To achieve this petal, structural engineers will need to coordinate the potential to reuse or salvage materials on the project and design for deconstruction at the end of the building’s lifecycle to mitigate the amounts of materials that end up in the landfill. Reusing existing structural materials on a project can help reduce the demand for new materials and the structure’s embodied carbon from the process of 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 proposed design’s demands. It is paramount that structural engineers are engaged during schematic design when building and material reuse is a design option.

With select structural systems, the initial costs of designing for deconstruction and/or  construction of the systems may result in a final design more expensive than traditional construction methods. However, savings may be achieved through reduced assembly. Overall, a whole life costing approach is a fairer comparison between differing approaches. 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. 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.

ILFI. (2019). Living Building Challenge 4.0. Seattle, WA. Accessed June 30, 2021. https://living-future.org/wp-content/uploads/2019/08/LBC-4_0_v13.pdf