Why use CLT for a parking garage?

January 25, 2018

By Kent Duffy

Architects at SRG have been fascinated by Cross Laminated Timber (CLT) for some time. In 2014, we awarded four SRG Travelling Fellowships, and the group traveled to Austria and England to see CLT manufacturing facilities and examples of innovative CLT buildings. Our recent CLT projects include the Oregon Zoo, our new Portland office space, and the CLT Parking Garage for the City of Springfield.

Our proactive approach to understanding CLT opened the door for us to be invited to a review for a studio at the University of Oregon led by Judith Sheine and Mark Donofrio. The City of Springfield wanted to know if it was possible to build a mass timber parking structure. They had a revitalization effort underway for the Glenwood neighborhood and a parking structure was a pivotal part of the plan. They also had a history of timber jobs and expertise, and they wanted to use the project to help revive the industry.

The studio generated a lot of enthusiasm for the project and the city decided to explore next steps. We worked closely with Courtney Griesel, Economic Development Manager for the City of Springfield, to prepare an entry for the Oregon Best CLT Competition for research money to support the exploration of the technical challenges of a CLT parking garage. We formed a core team that included Susan Gust, Lisa Petterson, Robert Lochner, Jim Wilson, Emily Dawson and myself from SRG along with Eric McDonnell and Anne Monnier from KPFF to undertake the challenge. We were assisted by Monica Anderson and Geoff Larsen from BHE Group, Mike Hatten and Grant Bowers from Solarc, Jim Krumsick from Paradigm Engineering, Elizabeth Anderson and Karen Ryan from Anderson Krygier, Scott Creighton and Larry Johnson from Womer & Associates, and Graham Roy of Rider Levett Bucknall.

We reasoned through some key issues and developed a design concept that was very successful in that competition. Of the $200,000 available to be awarded to projects, the City of Springfield received $155,000. That money helped support research at the Energy Studies in Buildings Laboratory (ESBL) at the University of Oregon and at the TallWood Design Institute (a collaboration between College of Design at the University of Oregon and the College of Forestry and College of Engineering at Oregon State University.)

The structure typically spans 60 feet to avoid drivers having to maneuver around columns in the parking bays. To accomplish this span, we used a pair of 36 inch deep glulam beams on either side of the column with top and bottom layers of laminated veneer lumber (LVL). By making the top and bottom layers LVL and using steel cables to post tension the beams, we could achieve this 60 foot span without the beams being enormously deep.

In terms of earthquake resistance, we have gone the extra mile. I don’t think there’s anything better to use than our post tensioned rocking CLT shear wall system, which moves back and forth in a seismic event and comes back to its original position afterward essentially undamaged. The seven layer CLT panels are connected to the adjacent glulam columns with “U” shaped steel spring connections that flex to absorb the movement of the seismic event, and then the post tensioned cables return the walls to their original positions when the event is over. In July, the system underwent a shake table test at UCSD which subjected the system to the equivalent of two sequential Northridge seismic events and performed exceptionally well.

This will likely be one of the first CLT parking structures in the nation, so we were determined to address each obstacle to such a structure and to provide a compelling response. We worked with a team from the City of Springfield that included the Building Official, the Fire Marshall, the City Engineers designing the streets and utilities, and the City Attorney. It was very valuable to have each of those voices at the table as we worked through a series of issues that arose as part of doing something for the very first time. An example would be deciding upon how to protect the wood structure from fire. Both the Building Official and the Fire Marshall were concerned about a wood building full of cars, so the building is fully fire sprinkled. We worked with the fire protection engineer and the structural engineer to find a very discreet way to integrate the sprinklers within the structural system.

We were also concerned about the structure being vulnerable to damage if it got wet. We asked the researchers at the TallWood Design Institute “what is at work when wood decays?” Their answer was “microbes, fungi and insects.” The key ingredient for these elements of decay is really moisture. While the site is near a river, and we are well outside the flood plain, we still raised all of the wood structure on a four-foot tall concrete base. Additionally, we were concerned about damage from wind-driven rain. We incorporated a perimeter pedestrian walkway that serves 70% of the parking spaces directly, so the pedestrians do not have to walk in the drive aisle. That perimeter walkway is framed in steel, and it also forms a protective sheltering layer for the wood structure within. What remained potentially exposed was the bottom half of the wood columns. ESBL researchers could tell us when it rains, which way the wind is blowing, and how hard, which allowed us to strategically position panels of stainless steel wire fabric to prevent the wind-driven rain from dampening the columns.

Photo Credit: Energy Studies in Buildings Laboratory

CLT is a renewable material that sequesters carbon unlike steel and concrete. The process to produce steel or concrete requires significant amounts of energy and also releases greenhouse gases. We also have the advantage of the first certified CLT plant in the nation, DR Johnson Lumber Company, being located in Oregon, so we can work directly with the manufacturer. Additionally, there is an expectation of the erection time for the 200,000 square foot parking structure being significantly shorter with the glulam and CLT structure than it would have been with steel or concrete. There is also an expectation of it requiring less shoring. Those are all convincing technical reasons in favor of mass timber, but there are also other reasons such as demonstrating the use of an innovative material to encourage exploration of it as a building material. Wood is a material that many people admire for its versatility, visual character, and the evident craft inherent to using it well. We are also delighted to have an opportunity to bring an artful dimension to what is often perceived as a utilitarian structure.

Wood has such a long history of being part of our culture here in the Northwest and that, along with the skilled jobs that this new industry is contributing to the economy, makes it an enticing material to use.

Katie Hunt, in our Seattle office, compared adoption of CLT to PV solar panels in that getting PV to be widely used required changes in construction policy and cooperation from engineers. CLT is more than just a new material, it’s a new way of construction. SRG is going to be at the forefront of how to make this new way of construction more common in our region. Since getting involved with CLT, we have spoken at numerous conferences to get this story out.

In a way, there may be a parallel with the Food Innovation Center project SRG did for the College of Agricultural Sciences at Oregon State University and the Department of Agriculture for the State of Oregon. The project was in recognition of Oregon ranking very high among the 50 states in terms of the percentage of its economy based in agriculture and very low in terms of value added to those products. We tended to ship raw products to others who added value to those products. For example, fruit would get made into jams and chutneys out of state, increasing the value of Oregon's produce. The food Innovation Center’s purpose was to assist Oregon based producers of agricultural products to add value to those products to strengthen their economic base and add skilled jobs to Oregon’s economy, in other words, making the jams and chutneys in Oregon. Similarly, Oregon has relied upon exporting logs to which value was added in other places. Now the emphasis is upon adding products, technologies, skills and expertise to the equation. With that in mind you should note that a new product, Mass Plywood Panels (MPP), is expected to be in production soon at Freres Lumber Company. Developing CLT and MPP technology here adds value to our wood resources and creates the types of wood technology that can have significant impact upon the wood products industry and the construction industry.

Last May, I joined a group organized by the TallWood Design Institute that toured Northern Italy, Austria, and Switzerland to visit more CLT manufacturing plants and buildings. The group included researchers, manufacturers, developers, and architects. We met with a number of European manufacturers, and we were exposed to the wide-ranging expertise that has developed along-side this technology as well as some outstanding projects that demonstrate its versatility. It was very interesting to see the diverse ways of approaching CLT technology and the range of applications that they chose to focus upon. Each one had a unique view and value, and the region was stronger for it. These technological advances have had a major impact upon the construction industry in Europe and have been exported around the world.

Note the incredible detailing on these CLT beams from Blumer-Lehman in Gossau, Switzerland
Curved and interlocking CLT members from Blumer-Lehman in Gossau, Switzerland


Zurich Zoo elephant habitat under a CLT dome

Really, that’s what's exciting about CLT - it's a new technology that will greatly benefit our built environment, our natural environment, and the place of wood in our culture.

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Kent Duffy

FAIA, LEED AP BD+C

Principal