San Mateo County Office Building 3

COB3
COB3
COB3

Located in Silicon Valley, the new San Mateo County headquarters will be the first net-zero-energy civic building constructed with mass timber in the U.S. Achieving an 85 percent reduction in structural embodied carbon, this flexible workplace sets a benchmark for civic architecture.

Project Facts
  • Status Construction In Progress
  • Completion Year 2023
  • Size Site Area: 0.75 acres Building Height: 72 feet Number of Stories: 5 Building Gross Area: 207,000 square feet
  • Energy Savings 609876 kwh
  • Water Savings 523395 gallons
  • Sustainability Certifications LEED BD+C NC (New Construction) Platinum, BD+C, Platinum
Project Facts
  • Status Construction In Progress
  • Completion Year 2023
  • Size Site Area: 0.75 acres Building Height: 72 feet Number of Stories: 5 Building Gross Area: 207,000 square feet
  • Energy Savings 609876 kwh
  • Water Savings 523395 gallons
  • Sustainability Certifications LEED BD+C NC (New Construction) Platinum, BD+C, Platinum

Civic leadership

When San Mateo County leaders approached SOM to design a new county headquarters, they had ambitious sustainability goals. Climate leadership is needed now more than ever, and this county on the San Francisco Peninsula is particularly vulnerable to the perils of climate change, including wildfire, drought, and sea-level rise. County leaders were also cognizant of the symbolic weight and long-term impact that this building will have. Civic buildings are built to endure for generations, and when purposefully designed, these structures become essential to the municipality’s identity. With its structural design that uses cross-laminated timber to reduce embodied carbon, County Office Building 3 (COB3) will stand as a testament to San Mateo County’s environmental stewardship.

COB3
© SOM

Designed for healthy city life

The design invites foot traffic from the neighboring downtown district along tree-lined walkways and into the building’s plazas and cafe. COB3 is configured in an H-shape that allows for two generous plazas which face, respectively, toward the city’s commercial center and toward the heart of the County Campus. Timber wraps the lobby interior, and wood slatting continues as a motif throughout the building, echoing the exposed wood structural frame. The abundance of natural wood creates a soothing, visibly low-carbon environment. All occupants will benefit from biophilic design strategies—the use of natural materials, natural ventilation, and views of the surrounding landscape. While the floorplate maximizes daylight throughout the interiors, the bridging floors, between the two wings of the building, create social collaboration hubs.

COB3
© SOM

COB3 was planned during the height of the COVID-19 pandemic, as emerging realities redefined public spatial needs. The building’s layout integrates the public safety measures with which we are all now familiar, and readies the building for future emergencies. The site plan includes space for a socially-distanced queue before entering the building. Four staircases offer multiple circulation paths, so that occupants will be able to avoid sharing elevators. Ample outdoor areas, like the promenade grove and two plazas, can be easily repurposed for outdoor meeting and working.

COB3
© SOM

Mass timber minimizes embodied carbon

Every decision in construction detailing and structural design was motivated by the goal of diminishing the building’s carbon footprint. Leveraging craftsmanship, engineering knowledge, and insight from the firm’s research on mass timber construction, SOM lowered the volume of timber in the building, reduced the piece count, and pared down the number of steel components. While a typical mass timber structure has 65 to 75 percent less embodied carbon than a conventional steel structure, COB3’s structural timber design lowered its structural embodied carbon by 85 percent.

COB3
© Cesar Rubio
COB3
© Cesar Rubio
COB3
© Cesar Rubio

Further embodied carbon reduction was possible through the elimination of materials–such as conventional hung acoustical ceilings, which were replaced by alternative acoustical solutions–and the specification of low carbon materials. Carbon associated with construction activity was also reduced by simplifying field connections. The prefabricated timber components make the construction process faster and more precise than conventional building processes.


Strategies for net-zero energy

Targeting LEED Platinum certification, COB3 will be the one of the first net-zero energy, ultra-low-carbon civic buildings in the United States. Solar arrays on site will produce the energy needed for the building’s operations. Passive design strategies reduce the building’s energy use. The glass enclosures on the building’s north and south facades are recessed and shaded, while, on the east and west sides, a series of fins protect the windows. These measures minimize heat gain, reduce the need for artificial cooling, and optimize daylighting. Rather than diverting stormwater runoff to municipal treatment facilities, onsite bioretention planters will absorb and treat 100 percent of the site’s runoff. These solutions reduce environmental impact throughout the building’s life.

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