2024 Award Winners and Nominees
Project Name
681 Florida Street Affordable Family Housing
Description
681 Florida Street Affordable Family Housing was a collaboration between Central Concrete (ready-mix supplier and subsidiary of Vulcan Materials Company, NRMCA member), Mithun (architect of record), Largo Concrete (concrete subcontractor), Cahill Contractors and Guzman Construction (general contractor joint venture) and affordable housing developer team Tenderloin Neighborhood Development Corporation and Mission Economic Development Agency. This project was a pilot project for the Bay Area Low-Carbon Concrete Model Code, funded by BAAQMD’s 2018 Climate Protection Grant Program as a first-of-its-kind effort to address embodied emissions in an area of local government control led by the County of Marin, StopWaste, Arup, the Carbon Leadership Forum, and the Ecological Building Network. As part of a small cohort of pilot projects, the 681 Florida Street design team received guidance in altering concrete specifications and engaging in early collaboration with concrete builders and suppliers. The result was a rich collaboration that achieved concrete across the project with significantly lower carbon content (discussed further below) as well as a beautiful building with various areas expressing the craft of concrete. As a project, this mixed-use development provides amenity-rich, family-friendly urban living. Rooftop gardens, generous ground-floor community space, and healthy materials contribute to a building for all ages. Highly coordinated systems design and careful cost analysis help achieve a fossil-fuel-free building with an EUI that meets the 2030 Challenge, ensuring high sustainable performance with low maintenance. The development supports displaced and low-income families with 30% of units reserved for formerly homeless residents with incomes 15-30% AMI; the remainder of units are available to residents with incomes 40-60% AMI. The project also provides spaces for a variety of programs and services, from job placement and tax preparation, to urban rooftop farming and healthy cooking classes. In support of cultural place-keeping in the Mission, a double-height performance and practice space for local arts institution Carnaval anchors the ground floor. A forecourt with a large art gate at the main entrance welcomes events as well as curious passers-by, activating the street and engaging the community in the arts.
Evidence
681 Florida Street stands as an example of the importance of early and consistent collaboration between builders and designers. Post-tensioned concrete construction was chosen early in the design process for its thin 8” floor slabs, which allows 9 stories of residential housing within 75 feet, avoiding costly high-rise designation while maximizing unit count. This is important on urban affordable housing projects, where cost-per-unit must be minimized to compete in the affordable housing finance market. No other structural system captured the low cost-per-unit. Concrete is also a durable material that property owners can trust, and therefore the concrete construction is exposed throughout the building – on the façade, exposed shear walls, polished concrete floors, and exposed ceilings within units. Most importantly, successful collaboration allowed the project to achieve a 36% reduction in embodied carbon of the concrete alone, which yielded a 23% reduction in embodied carbon across the entire project. This is compared to the base building specifications had they received no specification feedback and coordination from Central Concrete. These embodied carbon reductions were entirely cost-neutral, and allowed the ready-mix supplier greater flexibility in supplying supplementary cementitious materials. The methodology involves removing unnecessary requirements from the structural concrete specifications, such as water content and cement ratio, instead focusing the requirements of the concrete specifications on strength requirements. Because the subcontractor was also part of the collaboration, adjustments were made to ensure tight construction schedule restraints were met. The project also tested the process by which a project would be approved under new low-carbon concrete building code, which is now codified in the Marin County Building Code. The process is meant to be minimally bureaucratic, involving first, a simple worksheet that gets added to the project plans upon permit submission, and second, a verification worksheet submitted by the contractor. This and other successful stories of pilot projects has spread over the last few years, and is thus being considered in numerous other municipalities across California. While the model code is a technical step forward for more sustainable concrete, an even larger impact is the collaborative lessons that are spreading amongst designers, engineers, suppliers, builders, and owners.
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