Last fall, Kwan Henmi collaborated with DCI Engineers to participate in an international wood building design competition. “Plan B: The City Above the City” prompted our team to envision how mass timber construction could be used as a tool in the quest for socially responsible urban densification.
URGENCY
San Francisco is currently experiencing a housing crisis that threatens its residents. By 2030, the city’s population is estimated to increase by 150,000 people while adding only 9,000 new dwelling units. The gap between the amount of housing needed and housing provided for residents has widened for decades due to both limited developable land and hesitance to densify the city. This has led directly to ballooning housing costs and has irreparably damaged two of the city’s most valuable resources: community culture and historic architecture.
A history of displacement: Mapping building fires and no-fault evictions in the Mission District.
Data credit: http://www.antievictionmappingproject.net/fires.html
Historic neighborhoods like the Mission District have become battlegrounds of cultural identity and gentrification. Low-income residents are vulnerable targets for displacement, while consequential existing buildings are under constant threat of demolition due to both deterioration and new construction. This critical situation has inspired the Kwan Henmi & DCI Team to challenge the current battle and propose an alternative path forward.
PROPOSAL
‘Mission: Housing’ showcases mass timber products as a tool for alternative development, providing additional housing in the heart of the city without demolition of existing structures or displacement of existing residents. El Capitan Theater & Hotel, built in Mexican Baroque “Churrigueresque” style, is one of many exquisite historic resources falling into neglect whose ongoing viability is at risk. The original theater was demolished and used as a parking lot, while the hotel was converted into a Single Resident Occupancy (SRO). The opportunity and goal of this proposal is to build atop the existing structure with minimal intrusions to the existing structure and embrace the affordability aspect of its current use while reconnecting the site to the surrounding community.
CONCEPT
The building’s form is sculpted in reaction to its context through tapering and shearing actions. The resulting form is sensitive to the existing life of the street while increasing density. The skin system references Churrigueresque patterning, yet expands and shifts across its height to reveal lush gardens and an expanding array of delicate canopies.
The building’s original light well is extruded through the full height of the building, providing passive ventilation and natural lighting throughout the core. Communal spaces are provided for urban agriculture, irrigated via in-house greywater purification. This embedded horticulture purifies the air inside the building, provides nourishment for inhabitants and strengthens San Francisco’s tradition of civic parks.
PHASES
The building’s construction is proposed in phases, dependent on need. As the project grows over time, the building envelope will reach its final form. In 15 years, the project is projected to reach completion.
SYSTEMS
The adaptability of urban development could be revolutionized through the inherent strength of mass timber construction. Conventional concrete and steel construction is often impractical and expensive for multi-story units. High-rise construction using traditional wood balloon framing is not possible due to the risk of rapid spread of fire in lightweight lumber, which could quickly cause collapse. This issue is not a vulnerability in heavy timber construction, since fire creates a layer of charred wood on the exterior, which extinguishes the fire before the structural integrity of the system is compromised. The designed proposal creates an innovative new composite floor system from products, which are already available. It uses a concrete topping with steel shear plates embedded into laminated veneer lumber floor panels, allowing for longer spans. The sandwiched joists in this unique floor design allow the bottom panel to be removed and replaced in the event of fire damage, enabling the building to be reoccupied quickly after a fire. The heavy timber columns employ a steel plate connections, minimizing shrinkage between floors (see system assemblage images for more detail). This design’s final 26-level height is determined by the 260-foot allowable height limitation set by the building system. Since the construction process uses a modular set of components, this solution is highly efficient and flexible for design growth.
The building’s flexibility is enhanced by the lateral force resistance of post-tensioned laminated veneer lumber rocking shear walls, which can be recalibrated as necessary to maintain optimal strength or resolve shifts in structure after an earthquake. The high compressive capacity of these wall panels makes them incredibly resilient, handling large seismic forces while exhibiting minimal damage. For more information on the structural components, see DCI’s project summary.
MULTI-GENERATIONAL LIVING
The unit’s modular design allows for dwellings of any size to be easily adapted, allowing families and homes to grow in tandem. Creating narrower multi-level units densifies the building and provides a variety of dwelling typologies. The modules can be changed over time depending on resident’s needs, or adding on stories as families grow. This aggregational method works in conjunction with the building’s phasing.
CONCLUSION
Historically, urban growth has been obstructed by the false dichotomy between preservation and progress, but this can be changed. The innovative variety of mass timber technologies facilitates our strong and diversified strategy for sustainable evolution, which can strengthen and mature the fabric of the city.
