This section will dive into a high level overview of design strategies that can be implemented to reduce the embodied carbon of structural systems. A reminder of the [fundamental embodied carbon calculation]([[Example Embodied Carbon Calculation#Fundamental Calculation]]): $Embodied \: Carbon= \: physical \:quantity * carbon \: factor$ We can consider two classes of reduction strategies: 1. Material Efficiency – reduce the quantity of materials 2. Procurement – use less carbon-intensive materials # When can embodied carbon be reduced? The most influential time to reduce embodied carbon is at the outset. The window of opportunity significantly changes as the design gets more developed. ![[Reduction Strategy Curve.png]] # Hierarchy of Decision Making There is a hierarchy that can be followed when thinking about reductions. First, building less, and reusing more is a first guiding principle. Next, use low carbon systems. Third, design efficiently. And lastly, use low carbon materials. ![[Reduction Strategy Hierarchy.png]] ## Build Less, Reuse More This design strategy can go without saying. Reuse rather than new construction can save up to 80% of embodied carbon emissions. Identify opportunities to avoid new construction. The [CARE Tool](https://www.caretool.org) can be used to justify the use of retrofitting existing buildings. ## Low Carbon Systems By not choosing a structural system that inherently has high embodied carbon, there is much greater potential to realize reduction. By clearly defining the project goals to include embodied carbon (see [[Engaging the Design Team]]), it can be justified to select lower carbon structural systems. One effective strategy is to set embodied carbon targets either at the material, component, or whole-system level. These carbon targets can be either an absolute limit (e.g., lt;400 kgCO_2 e/m^2$ for the structural system), or a reduction from a baseline (e.g., < 20% less than a typical structural system for this building typology). One way to evaluate different structural systems is to design a typical bay and perform a simple embodied carbon assessment. More advanced workflows can include developing parametric analyses that can optimize system selection for a given site and set of design constraints. ## Design Efficiently Once the structural system is chosen, the next best design strategy is to design efficiently. Typically, the simplest and lightest structure has the lowest embodied carbon. Try to avoid "structural gymnastics" and convey the importance of simple load paths to the rest of the design team. Lower cost configurations (i.e., material efficient spans) are typically low embodied carbon too. Designing efficiently is synonymous with good structural engineering. Consider maximizing structural depths of members to take advantage of what we know of structural mechanics. But be aware of the other impacts that might be associated with increasing floor depth. For example, increasing member depth may reduce the embodied carbon of the beams, but will increase the embodied carbon of the columns as well as the building envelope. Considering the unintended consequences is important when evaluating any design strategy. Ensure that all structural components are fully utilized by optimizing the structural design. This optimization needs to be balanced with standardization to reduce construction waste. Consider using the right material for the given context. If lower grade materials can be used (i.e., concrete), then use those lower grade materials. Don't over-design. Basements and sub-grade construction requires more structural material, in addition to excavation (Module A5) emissions. Work to minimize the amount of sub-grade construction and other carbon intensive structures. As a summary, consider the following strategy for both gravity and lateral systems: ### Gravity System - Use shorter spans. - Use regular spacing of vertical elements. - Avoid transfer elements. Specifically, transfer floors in a building lead to much larger embodied carbon impacts. - Use structurally efficient (low-weight) floor systems: Post-tensioned, ribbed, or void concrete slabs. Deeper metal deck and/or castellated steel beam. Point supported CLT slabs or mass timber panels on purlins and girder beams. - Consider the impacts of fire proofing that is dictated by the choice of structural system. - Work with the geotechnical engineer to identify the lowest carbon solution. Lighten the structural system as much as possible to minimize foundation loads. ### Lateral Systems - Embrace symmetry. More symmetric buildings reduces the need for collectors and reinforcement needed to resist torsion. - Avoid short and slender vertical elements that are not efficient in resisting overturning. - Use higher ductility systems or energy dissipation systems. ### Reduce Building Height Consider the height of your building. Taller buildings pay a premium for embodied carbon due to the additional loading both for the gravity and lateral systems. The relationship is non-linear between increasing building height and normalized structural system embodied carbon. Check out the work of [James Helal](https://doi.org/10.1016/j.istruc.2020.01.026) and [Vincent Gan](https://doi.org/10.1016/j.jclepro.2017.05.156). ## Low Carbon Materials Once a structural system has been designed as efficiently as possible, additional reductions can be made as part of the selection of low-carbon materials. For example, using supplementary cementitious materials (SCMs) in place of ordinary portland cement can reduce the concrete embodied carbon. There are many material-specific procurement strategies, which are outlined will in the [SE 2050 Specification Guidance](https://se2050.org/resources-overview/structural-materials/specification-guidance/). # Additional Resources The SE 2050 web page goes into more depth than this page on design strategies and guidance for reducing embodied carbon: [Design Guidance for Reducing Embodied Carbon in Structural Systems](https://se2050.org/resources-overview/structural-materials/lean-design-guidance/). The [IStructE has resources](https://www.istructe.org/resources/climate-emergency/) on (2) Low Carbon, (3) Lean Design, and (4) Zero Waste which are another good starting point for getting inspired to develop your own low-carbon designs. # Navigation Return: [[Home]] Suggested Next: [[Prestandard for Assessing the Embodied Carbon of Structural Systems for Buildings]]