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633 Folsom office building, as seen from the street

633 Folsom Offices

Reimagining and expanding an existing 100,000-square-foot structure with a vertical addition clad in a new skin.

  • Advanced Analytics

    Nonlinear response history analyses led to a lean, cost-effective approach to harness the strength of the existing structure with targeted strengthening for the expansion.

  • Sustainable Integration

    Repurposing the 60-year-old structure with targeted measures results in a far lower carbon footprint than building new. (Certified LEED Gold, anticipates WELL building certification)

  • Seismic Resilience

    Advanced seismic-shaking simulations informed a resilient design that protects the building's users and limits the downtime and damage after an earthquake.

  • Integrated Value

    Partnering with the developer and architect and contractor from the onset, the team devised an integrated approach to reimagine the aging property into a “Class A” office tower.

We harness our advanced analytics’ capabilities to predict structural behavior and gain key insights to develop optimized, data-driven design solutions—creating real value for clients and building owners.

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We’re hyper-focused on providing useful insights early in the design process to better inform key decisions, control cost, and minimize disruptive surprises. By internalizing project-level goals, we’re better able to help achieve them.

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As industry leaders, we collaborate and innovate to create low-embodied energy, sustainable design solutions that are efficient, cost-effective, and seek to reduce carbon output to minimize construction’s environmental impact.

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We combine innovative design and a collaborative and responsive workflow to deliver tailored, effective, and unexpected seismic design solutions that help protect our clients’ high value investments and facilitate post-earthquake operations.

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Instead of textbook solutions and conventional approaches, we ask deeper questions to unlock possibilities. Through ingenuity and a thoughtful application of engineering first-principles, we develop more responsive and efficient structural designs.

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Originally developed by The Swig Company in 1966, the aging midrise structure at 633 Folsom no longer attracted modern tenants looking for a corporate home in downtown San Francisco—the brick facade was dated and the 20-foot column grid didn’t meet the space planning needs of contemporary workspaces. Tipping and the rest of the design team were brought in to help the Swig Company realize their vision of transforming the building into a “Class A” office tower.

Project Challenges

The 1960s building was seismically outdated, and the vertical addition posed another level of complication to both the gravity and seismic retrofit design. To compete with newer buildings, the structure would need to offer long-span flexible workspaces—much wider than the 20-foot column grid that existed in the 60-year-old structure. 

A Modern Transformation

Tipping and team’s unconventional and ambitious approach created a five-story vertical efficient steel framed addition with a 40-by-40 column layout and a new iconic glass facade, doubling the leasable space and transforming a dated building into a modern “Class A” office tower with a small core footprint. Through performance-based engineering, innovative design, and a collaborative process among the design team, the existing building was reinvented, once again inspiring its users and contributing to a vibrant community. 

  • Location

    San Francisco, CA

  • Square Footage

    278,000 sf

  • Cost

    $75 million

  • Completion Date



    2021 SEAONC Excellence in Structural Engineering, Award of Excellence, Retrofit/Alteration

    LEED Gold Certified

    2022 AIASF Architecture Merit Award

  • Owner

    The Swig Company

  • Architect


  • Contractor

    Plant Construction Company

  • Developer

    The Swig Company

  • Photography

    Jason O’Rear

Tipping brought a thoughtful strategy to seismic resilience of a midcentury building carrying the load of a major addition. They added significant value through targeting performance-based improvements based on modeled analysis which gave us great confidence in the relevance of the investment. It has been a very collaborative experience to work with the Tipping team: supportive in achieving design goals and reconciling the inherent discovery process of renovation work, from design through construction.

- Brent Van Gunten AIA, Principal, Gensler

Sustainability through repurposing

While demolishing the existing structure and erecting a new building may have been an easier approach, there were many reasons that adapting and expanding the existing reinforced-concrete structure was a wiser decision:

  • Repurposing the structure brought inherent sustainable advantages and avoided the excessive waste of demolishing the seven-story structure
  • In 1994, Tipping had performed a voluntary seismic upgrade on the building, which provided added strength
  • Vertically expanding the property by five floors offered an opportunity to nearly double its leasable square footage and increase desirability among tenants
  • The project also had the advantage of avoiding a lengthy entitlement and permitting process by gaining approval under San Francisco’s Proposition M and the Office Development Annual Limit Program

An innovative structural approach

Tipping took a performance-based design approach, relying on nonlinear response-history analyses, which took into account the response of the original structure, the retrofit measures of 1994, and the new design. Through advanced seismic-shaking simulations, an optimal design scheme was honed to maximize the reuse of the existing structure and limit required strengthening.

The five-story addition on top of the existing concrete structure consists of a new steel frame with a 40-foot-by-40-foot column layout, strategically configured to minimize added weight and reduce the need to strengthen existing columns and foundations.

The new facade with glazing and integral GFRP sunshades are seamlessly integrated with the new and existing floors. To accommodate the cladding panels, the slabs at the existing floors were extended 24 inches and provided with custom embedded anchorage.

Greater seismic resilience through precision retrofitting

The retrofit and expansion strategy extended the existing core vertically to support the new steel-framed levels, and expanded the structural core at the lower eight stories. New foundations with micropiles were added to resist overturning forces under the new expanded core, while carbon-fiber reinforced polymer CFRP collectors strengthened the existing floors and connected to the new core walls. The thin profile carbon-fiber strengthening was chosen to reduce the impact to ceilings and minimize costs.

The existing core was extended to the new steel-framed levels, and a new core was added within the existing structure.

Surgical demolition and reconstruction of the core at the eighth floor was required to extend the core into the upper floors.