Engineered wood products provide a strong yet light alternative to concrete and steel.
Stepping inside 1 De Haro, San Francisco’s first mass-timber building, feels a bit like entering a spruce forest. Honey-colored wood stretches along the ceiling, down the timbered columns and across the floor. Its woody fragrance permeates the space, a reminder of the grove of trees that, until recently, grew in a Canadian forest.
San Francisco-based SKS Partners, in partnership with a local family who has owned the site for nearly 100 years, embarked on constructing the four-story, 130,000-square-foot building in December 2018 with completion slated for October 2020. Situated on a corner, its distinguishing pointed edge has been dubbed the “shark tooth,” a harbinger of differentiated construction materials. The building will house a mix of office and light-industrial uses. While sustainability and construction speed prompted the developers to use mass timber, they quickly realized its other benefits.
A Mass-Timber Primer
Mass timber buildings use solid or engineered wood, such as panels and cross-laminated timber, to bear the structure’s load. An engineered product in which several layers of wood are laminated and compressed, CLT (cross-laminated timber) is part of a wide — and growing — range of products under the broad category of mass timber. CLT uses boards set at right angles to one another, which are then laminated to create panels that can be used in floor, wall and roof assemblies. Proponents of mass timber tout its sustainable elements, reduced labor and construction times, and pleasing aesthetic.
Of course, consideration of sustainability involves a myriad of factors — product, manufacture, delivery and impact on occupants. In 1 De Haro’s case, Nordic Structures and its sister company, Chantiers Chibougamau, harvested the timber from a Canadian forest the size of Connecticut. The timber, black spruce, has a 50-day annual growth cycle in the cold northern climate. Innovative lamination processes allow wood providers to make the most of the entire tree, including the crown and small branches typically left behind on the forest floor.
The long-term environmental impact of these materials could be substantial. Using sustainably managed wood products instead of steel and concrete could help reduce global CO2 emissions somewhere in the 14% to 31% range, according to Yale and University of Washington researchers.
Further, sustainability advocates argue that the entire journey — from forest to installed wood panel — uses fewer resources and costs less than traditional steel or wood. For example, the wood product weighs about one-fifth as much as concrete or steel. As a result, when Nordic Structures placed the prefabricated panels for 1 De Haro on a train from Montreal, Canada, to Stockton, California, the transportation consumed far less energy than needed for heavier materials. The result, according to John Fisher of SKS Partners is, “a dramatically reduced construction carbon footprint vs. a concrete or steel building.”
Construction Cost Savings
While mass timber’s direct cost is higher, its indirect costs are lower, making the overall cost equation difficult to untangle. At 1 DeHaro, the premium timber material expenses were offset by reduced labor and a shortened schedule, resulting in construction costs equal to those of traditional steel or concrete. Industry estimates place premium materials at a 20% to 25% increase. A 2018 case study by the Central City Association of Los Angeles suggests that mass timber construction costs 5% less than the same project constructed from concrete.
The prefabricated nature of wood panels reduces labor costs and trash, and shortens construction times. Fisher notes that a crew of six workers installed 1 De Haro’s CLT panel system for the 30,000-square-foot floorplates rather than the 30 or more individuals typically required for a concrete pour of the same area. Research estimates that construction schedules are 20% shorter when using mass timber products. While the COVID-19 pandemic slowed 1 DeHaro’s progress, that time-savings estimate proved applicable. In turn, the rapid installation by fewer workers can translate to abbreviated construction schedules that allow for rent-paying tenants to occupy the space sooner.
Additionally, there’s little need for expansive on-site staging areas, a boon for urban or tight sites. Owners realize added savings by cranes they don't need to rent and the inefficiencies of storage and a second staging.
Despite environmental and scheduling advantages, mass timber construction faces some hurdles due to the relative scarcity of such projects. For instance, the market lacks an established supply chain. Developers can encounter a small field of experienced contractors, which becomes problematic when seeking competitive bids. And contractors and owners may contend with insurance policies that reflect traditional wood-frame construction as opposed to mass timber. A November 2018 case study by the DLR Group, “Tall with Timber,” states that “products such as cross-laminated timber have been proven through rigorous testing to externally char and maintain structural integrity in a fire situation.”
Regardless of construction speed, code compliance can be a complicated web. Currently, light or mass timber can be used to construct commercial buildings up to 85 feet tall, and can exceed these heights only with extensive testing and documentation. Newly adopted rules in the 2021 International Building Code, however, will allow for timber structures up to 18 stories tall. Additionally, California-based developers face an array of seismic codes. These encourage owners to consider the relatively lighter mass-timber because weight drives seismic force. And as Fisher observes, the lighter weight required 150 piles rather than 300 at the 1 De Haro project. That’s important, because Fisher says “pile driving is the riskiest thing we do” thanks to the unknown subterrain.
In 1 De Haro’s case, the four-story commercial building contains a first floor constructed of concrete, with the upper three floors made of mass timber. The overhead beams fit cleanly into place, in a sophisticated Lincoln-log style. And while sprinklers and lighting are surface-mounted, there are intermittent holes cut into panels, minimizing the ceiling clutter. The exposed wood lends a warmth and texture to the space that create a unique yet welcoming office environment.
1 De Haro’s owners, in the space grab that so often defines the current San Francisco market, leased the entire building to one tenant before the last wood beam placement.
1 De Haro’s owners proved willing to exchange traditional building for a sustainable approach with little change to construction costs. In fact, some may argue that the beauty and health inherent in a wood building allowed this owner the potential for higher rents and quicker occupancy, leading to greater economic benefit. San Francisco’s first mass-timber commercial building created a built environment that might make working at the office seem like a stroll in the park.