Spanning 208,000 sq ft, the $195-million County Office Building 3 (COB3) is the first net-zero energy, LEED Platinum, mass timber civic building in the U.S. Completed in April 2024, this H-shaped, five-story structure features a mass timber and glulam frame along with a cross-laminated timber (CLT) deck structure. Carbon reduction was top of mind with regard to materials and construction activities.

The all-electric building’s timber frame was selected for structural and environmental benefits, while the narrow structure facilitates natural ventilation and lighting, reducing the energy load. Structurally, the lightweight nature of wood allowed for smaller foundation sizes as well as high performance when subjected to lateral seismic loads. By using a CLT structure, the facility also achieved an 85% reduction in embodied carbon.

Photo courtesy Rowan Jack

COB3 features a high-performance envelope, mixed-mode ventilation and onsite renewable energy. Compared with other buildings its size, the facility will save around 610 megawatts of power and more than half a million gallons of water per year. Solar arrays will produce energy for building operations, while passive design strategies reduce energy usage. To minimize heat gain and optimize daylighting, glass enclosures on the building’s north and south facades are recessed and shaded, while a series of fins protect the windows on the east and west sides.

When the project began, the team established a project charter to set measurable outcomes, identify key decision makers and define how the team would work together. This proved a vital tool when mitigating the impacts of the unprecedented amount of rainfall that Redwood City experienced throughout the project’s duration.

Photo courtesy Rowan Jack

The team collaborated on a single BIM model during the long lead time required for mass timber to understand any conflicts and resolve them early. Additionally, 4D scheduling helped with the complex CLT installation sequence that required extensive coordination.

Although the project team was set to purchase CLT during the height of the pandemic, Truebeck went through an extensive prequalification effort to identify companies with the experience and financial backing to furnish and install the mass timber package turnkey. The team locked in material pricing in three separate phases, anticipating that pricing would reduce over a six-month period. By procuring timber in three phases, the contractor saved the county more than $1 million in material costs.

While a typical mass timber structure has 65-75% less embodied carbon than a conventional steel structure, COB3’s structural timber design lowered its structural embodied carbon by 85%. When it came time to install the mass timber panels, SOM created a steel bucket connection specifically for the project that allowed the beams to fly in straight off the delivery trucks and sit on columns without needing screws or bolts. The timber components make the construction process faster and more precise than conventional building processes. This allowed workers to maximize efficiency through repetition. Beam sizes also cut down on the total number required, reducing crane picks. The beams were designed to sit side by side, requiring a five-layer CLT instead of a more costly seven-layer CLT.