Developing Cost-Feasible Decarbonization Strategies for the Presidio Springs Affordable Housing Redevelopment

We conducted lifecycle carbon modeling for the Presidio Springs Redevelopment using three scenarios: a Baseline model representing the current design, a Moderate model consisting of low-carbon strategies that remain within a 10% cost increase threshold, and a Reach model exploring deeper decarbonization strategies that require additional design changes or capital investment. Within these models, both lifecycle embodied carbon from material substitutions and operational carbon from building energy use were modeled over a 100-year building lifespan. Results show that embodied carbon is the dominant driver of long-term emissions, particularly from material production (A1-A3), making early material procurement decisions critical.

The largest reductions in the Moderate scenario come from two major design changes: replacing conventional concrete with fly-ash concrete mixes and reducing finish flooring by refinishing exposed concrete slabs to resemble tile, which together account for the majority of emissions savings. Additional low-cost substitutions include switching from standard to recycled-content gypsum wallboard, recycled insulation, and recycled clay tile roofing, further lowering embodied carbon with minimal cost impact. These strategies achieve a 16.7% reduction in embodied carbon, avoiding 2,527,620 kg CO₂e relative to the baseline design. The moderate scenario also incorporates a high-efficiency HVAC system, which reduces modeled operational emissions by approximately 12%.

The Moderate scenario also considers additional strategies such as smart thermostats, which could reduce HVAC energy use by approximately 10-15%, and sustainable deconstruction practices to increase construction and demolition waste diversion beyond the 65% CALGreen requirement. However, these strategies were not directly modeled in the lifecycle carbon assessment and are presented as complementary measures that could further improve environmental performance.

The Reach scenario demonstrates that deeper emissions reductions are possible through additional strategies, such as replacing conventional concrete masonry units with lightweight, high-strength units. Additional operational reductions are achieved through strategies such as tightening the building envelope and improving overall building efficiency, which lower heating and cooling energy demand. Together, these strategies achieve approximately 18% embodied carbon reduction and 14% operational carbon reduction relative to the Baseline design. Greywater reuse systems, which could further reduce potable water demand and the energy associated with water treatment and pumping, were not modeled in this assessment but represent an additional opportunity for future reductions.

In summary, the moderate scenario provides the strongest carbon reduction per dollar invested, while Reach strategies represent a pathway for deeper decarbonization when additional funding, incentives, or policy requirements are available.

Acknowledgements 

Housing Authority of Santa Barbara: Dale Aazam, Deputy Executive Director / Real Estate and Technology; Christine Peirron, AIA LEED AP; Rob Fredericks, Executive Director / Chief Executive Officer; Hector Torres, Building & Facilities Construction Coordinator; Jacqueline Pollino, Property and Development Analyst

UC Santa Barbara Bren School: Dr. Mark Buntaine, Professor (faculty advisor), Dr. Eric Massanet, Professor and Mellichamp Chair in Sustainability Science for Emerging Technologies; Dr. Roland Geyer, Professor

Dennis Allen, Dean's Council (external advisor)