Structural engineers can make significant contributions to projects with sustainable design goals. Thornton Tomasetti is the engineer of record for the Jacob K. Javits Convention Center renovation in New York City. The project, which includes a massive green roof, is expected to achieve a LEED Silver rating. Lorenzo Sanjuan/Thornton Tomasetti.
Structural engineers are important partners in the design of sustainable buildings because the decisions we make can impact a project’s waste generation and energy use, as well as its lifecycle impact on climate change. A project is better served by structural engineers who implement strategies for achieving sustainable goals.
As the first structural engineering firm to join the AIA 2030 Commitment, we have pledged to work toward a carbon-neutral built environment. This commitment is primarily about the projects we design.
The following top ten list suggests questions in three categories that we can ask clients as a means of initiating a conversation about sustainability as it relates to structural design.
1. Do you anticipate that this building may someday be used for a different purpose? Well-designed and maintained buildings often outlive their first occupants. Institutions, in particular, may recognize the advantage of an easily reconfigurable facility. To address future use, structural engineers could adjust design load criteria, opt for more consistency in framing or avoid upturning beams or concealing braces in removable partitions.
2. Have you considered the building’s end of life? Designing for deconstruction allows for easier reuse of components without downcycling, which is a recycling practice that involves breaking down an item into its component elements or materials. Once the constituent elements or materials are recovered, they are reused if possible, but usually as a lower-value product. For example, reusing existing steel beams is less energy intensive than transporting back to the mill, melting back down to molten steel, re-rolling and re-fabricating. Avoid welded connections and continuous cast slabs. Precast concrete elements and some proprietary systems may be good options for material reuse.
3. In the event of a natural disaster, does the building need to remain operational and do employees need to return to work immediately? Would the owner accept aesthetic but not structural damage? Beyond designing for code minimums, structural engineers can apply techniques like performance-based design to limit replacement costs following extreme events.
4. Do MEP calculations account for the building’s thermal mass? Exposed structural slab and walls collect and radiate heat, effectively offsetting the heating and cooling cycles from peak times. This analysis requires sophisticated modeling, which can be performed by our Sustainability practice, as well as intimate knowledge of the structure.
5. Have you considered a hydronic heating/cooling system integrated with the structure to meet occupant comfort requirements? Radiant heating is more comfortable at lower ambient air temperatures. Structural engineers can work with mechanical engineers to offer an integrated solution for both composite steel and concrete structures. Our Sustainability practice can model comparisons between hydronic and forced-air systems in the early design stage.
6. Does any structural element protrude through the enclosure insulation? Thermal bridging may result in heat loss/gain through the enclosure and condensation inside. Details that minimize the bridging area and use less conductive materials to break the thermal conduit are available for windows, lintels, shelf angles, canopies, dunnage and foundation walls, to name a few. Proprietary systems are available, but are not the only approach. Heat transfer analysis can also be performed to confirm whether a particular thermal bridge is truly problematic. Our Façade Engineering
7. Does the framing layout support your daylighting goals? Structural engineers are trained to design for member efficiency, but maximizing daylighting may require using a shallower yet heavier spandrel. Also, columns or structural walls can interrupt daylight entry at the first interior support. A longer first bay might clear this space. Our Sustainability practice is well-versed in daylight analysis and can work quickly with your design team using simple rules of thumb, quick parametric runs or detailed space-by-space daylight studies using a variety of computer simulations.
China’s Shanghai Tower is both super tall and super green. The 632-meter building achieved LEED Platinum and China Green Building Committee Three Star ratings, thanks to an integrated approach used by the project team of Gensler, Thornton Tomasetti and Cosentini that ensured all design decisions followed a sustainable intent. Photo courtesy Reinhold Moeller/ Wikimedia Commons.
8. Have you considered embodied carbon as a design criterion? Sustainability goals for the project may include the reduction of greenhouse gas emissions from operational energy and also from embodied energy. Embodied energy is the energy used for the extraction, refining, manufacturing and transportation of building materials. Structural materials account for more than 50 percent of all embodied energy in a building. Along with strength, serviceability, constructability and cost, embodied carbon can be quantified and measured against other design options. It may be worth seeking this comparison for atypical structural moments, like column transfers, Vierendeel trusses, long cantilevers, sloping columns, etc. Additionally, concrete and steel approaches can be compared from an embodied carbon perspective. It can be yet another factor when comparing cost, timeline, material availability and regional sub-contractor expertise.
9. When advising on demo or reuse, have you considered the embodied carbon value of the existing structure? A carbon assessment based on material quantity can be performed on an existing structure. Strategies like building overcladding can preserve the existing structure while encapsulating the old failing façade and creating an exterior interstitial space for new mechanical systems and conveyance.
10. Can we use less cement? The binder within concrete is a product of an energy intensive process. Cement volume can be reduced with the addition of supplementary cementitious materials like fly ash, slag and silica fume. Lower cement mixes are possible if concrete strength is reduced and cure times are extended.
Have these questions in mind during your next consultant coordination meeting. They will give you a reason to stay engaged and an opportunity to demonstrate how structural engineers think holistically about building systems. You might impress a client. Most importantly, a more sustainable building might eventually take its place in the built environment.
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