The Tidelands | Life-Cycle Analysis

The Tidelands

Case Study

2021

Whole Building Life-Cycle Analysis

UC San Francisco The Tidelands INTRODUCTION TO LCA AT K I E R A N T I M B E R L A K E

To understand the full carbon impacts of building operations and construction, KieranTimberlake uses Life Cycle Assessment (LCA) to evaluate the embodied environmental impacts of building materials and assemblies. When paired with energy modeling, LCA is an important tool to help identify strategies to decarbonize our projects. LCA models measure impacts according to a range of categories, including global warming, acidification, eutrophication, smog formation, ozone depletion, and the depletion of non-renewable resources.

When applied to the scale of a full building, WholeBuilding Life Cycle Assessment (WBLCA) can evaluate the embodied environmental impacts associated with the manufacturing of materials, the construction and demolition of the building, and the disposal of the materials after their use. At KieranTimberlake, WBLCA serves to help a project team make decisions to reduce the embodied environmental impacts of the project.

WBLCA METHODOLOGY

LCA Scope: Modules A1-4, B2-5, C2-4, D.

INTRODUCTION TO PROJECT

The UC San Francisco Minnesota Street Housing at the Tidelands comprises two buildings providing 595 housing units for medical residents, commercial space on the ground floor, and below-grade parking. Construction of the 390,000 sq. ft. complex was completed in 2019. Both buildings use the same reinforced concrete structural system and envelope system. The lower stories are largeformat storefront glazing with tile, and the upper envelope is a self-shading, shaped glass fiber-reinforced concrete panel system.

The final embodied carbon intensity of the buildings is 238.3 kg CO2 /m2, a significant improvement over the Carbon Leadership Forum’s 2017 baseline for multifamily residential buildings of 453 kg CO2 /m2, based on 66 models.

PROJECT FINDINGS

In this project, KieranTimberlake used iterative LCA on smaller assemblies and design options throughout all design phases in order to reduce the embodied impacts of each scope of design, including the envelope, the structure, and interiors. The first WBLCA measured full-building impacts at the end of the 100% CD design phase.

Included Model Scope: Substructure (including deep drilled foundation), superstructure, enclosure, below-grade parking, interior partitions, and finishes for two residential buildings, as modeled in Revit Excluded Model Scope: Railings (<1% by mass), casework, furniture, MEP, landscape elements, and site work LCA Software and Version: Tally® version 2017.06.15.01 Reference Building Life: 60 years Biogenic Carbon: Included Module D Credits: Included

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Within the envelope, the design team tested two primary materials for the shaped facade panels: thin precast concrete and glass fiber reinforced concrete (GFRC). Isolating the two materials found GFRC had significantly lower impacts.

For example, GFRC had approximately 80% of the embodied carbon of the precast option. However, to ensure an even comparison across the entire envelope assembly, the backup steel framing structure of the GFRC was increased to account for differences in weight and shaping technique of the panel types. In addition, as the precast concrete panel provided some thermal resistance, additional insulation was added to the GFRC option in order to maintain a consistent U-value for both options. After these adjustments were made, the two options were significantly closer in performance, with the GFRC 95% of the embodied carbon of the precast concrete panels.

Using lessons learned from previous WBLCA projects, the KieranTimberlake team also looked at insulation type substitutions to reduce embodied environmental impacts. In this case, mineral wool insulation replaced polystyrene. Although the two insulation types have significantly different quantities of embodied environmental impact in isolation, when viewed in the context of the whole building, the reduction in embodied carbon attributed to the change in insulation type was only 1%. This is in part due to the small quantity of insulation required to meet the energy performance needs in the mild San Francisco climate.

The KieranTimberlake team also targeted embodied carbon reductions in the The high-performance envelope of each building consists of eye-catching, self-shading fins that manage sunlight.

interior finishes, using LCA as an input for selecting the final flooring assembly.

After conducting an LCA comparison of the resilient flooring options, the team considered a rubber flooring tile, a reduction of close to 50% from the common institutional housing standard, which requires vinyl composition tile. However, when viewed in the context of the WBLCA, the reductions in embodied environmental impacts due to the flooring change were negligible and a vinyl plank system was selected instead due to maintenance concerns.

The final change in building design was a collaboration between KieranTimberlake and Tipping, the structural engineering firm on the project. Leveraging Tipping’s experience with low-cement content concrete mixes, the team reduced the cement content of the superstructure to 50% of that in traditional concrete, an improvement over the already impressive regional baseline of a 30% reduction. When these reductions were added to the reduction of cement content in the foundations, the change in cement content was the most notable factor of the WBLCA results.

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VCT FLOORING

30% SUPERSTRUCTURE FLY ASH

RAINSCREEN POLYSTYRENE INS

PRECAST FAÇADE

100% CD

100% 90%

PERCENT REDUCTION (%)

80% 70% 60% 50% 40% 30% 20% 10% 0%

Acidification Potential (kgSO2eq)

Eutrophication Potential (kgNeq)

Global Warming Potential (kgCO2eq)

Ozone Depletion Potential (CFC-11eq)

Smog Potential (kgO3eq)

Primary Energy Demand (MJ)

Non-renewable Energy Demand (MJ)

Renewable Energy Demand (MJ)

Total Mass (kg)

ENVIRONMENTAL IMPACT CATEGORIES

L C A R E S U LT S

OPPORTUNITIES FOR IMPROVEMENT

Figure 1 Graphs showing WBLCA results at 100% CD and the individual changes associated with each of the original design options in isolation.

Life Cycle Assessment is an emerging practice. We view every WBLCA as an opportunity to reduce embodied carbon and evolve our practice, and we hold ourselves to the highest standard while conducing WBLCA. In the interest of ongoing improvement of our efforts and promoting LCA across the profession, this project helped us mature our practice in the following ways: •

Establish a benchmark model early to calculate total carbon reductions more easily

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Staying abreast of developments in low-concrete mixes in the industry and communicating closely with structural engineers and construction management throughout a project can help design teams respond to changes made during construction without sacrificing carbon goals and targets

On this project, the team used iterative LCA to test design options throughout the project, leading to rapid feedback alongside other design drivers. This modeling practice is similar to that of creating early phase generic models to test specific energy conservation strategies at the beginning of net zero energy building design. However, since a whole-building model only occurred late in the project, it is challenging to communicate “total reductions” because there is not a single option to compare as a baseline. We find with many projects, the more integrated LCA is into the process the more challenging it seems to create a theoretical benchmark or baseline building. Ideally, the team would run a benchmark model during DD, or at an appropriate point to better capture and evaluate the effect of early design decisions.

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The Tidelands was a technically challenging project with a rapid design and construction schedule. Our project experience continues to show that wellcoordinated, early engagement with structural engineers on the project team can have a large benefit to reducing the embodied carbon of concrete and creating a broad array of carbon reduction strategies in addition to cement replacement. By working more closely with structural engineers and construction management (CMs) on the project, teams have a better chance of finding cost-effective, project-specific decarbonization strategies that endure through project completion and meet all the technical requirements of design and construction. The abundance of experimentation in low-concrete design means design teams will need to work hard to stay up to date with changing technical guidance, local material availability, and climate-specific concerns that may arise during construction. Through better team communication, shared goal setting, and improved real-time carbon accounting to track the numerous concrete mixes on any one project, teams may be better able to respond to changes made during construction without sacrificing whole-building carbon goals and targets.

LESSONS LEARNED

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Early phase WBLCA is important to identify target areas for embodied environmental impact reductions effectively.

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(foundations and superstructure) often dominates a building’s embodied

L C A R E S U LT S

The combined embodied carbon contributions of the three (ed. note: I thought it was just two buildings?) buildings at 50% Design Development. Concrete accounted for the greatest carbon impact, at 64%.

REFERENCES

Simonen, K., Rodriguez, B., Barrera, S., Huang, M., (2017) CLF Embodied Carbon Benchmark Database, database. Available at http://hdl.handle. net/1773/38017.

In multi-story buildings located in seismic zones, concrete structure environmental impacts.

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Early and ongoing coordination with a structural engineering team that has experience in low carbon concrete mix design can yield significant reductions in embodied carbon of concrete buildings.

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Design teams should engage structural engineers on the project team to work together to set performance targets that include embodied carbon for

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all concrete mixes on the project.

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Additional, site-specific research may be needed to determine if concrete mix design strikes the right balance of being achievable, cost-effective, and

PHOTO CREDIT

ambitious in its carbon footprint. Teams should engage contractor early in

Bruce Damonte

the process, if possible.

C O N TA C T

Efrie Escott KieranTimberlake 841 North American Street Philadelphia, PA 19123 (215) 922-6600 efriedlander@kierantimberlake.com C A S E S T U D Y UC SanFrancisco The Tidelands

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Architects, engineers, and contractors should work together to establish a process for tracking carbon performance of all concrete mixes delivered to site during construction. A portfolio approach which allows for trade-offs in increased carbon in one part of the project to be balanced by further reductions in another may give teams the greatest flexibility to respond to necessary changes during construction while maintaining project goals.

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