Building A Rammed Earth Lobby Wall For American AgCredit - The First Of A New Journey / by Alex Wright

The first thing you see walking into the new headquarters for American AgCredit is the rammed earth wall, built with different strata representing the diversity of soils in the regions served by this bank for farmers. The wall itself is forty feet long, twelve feet tall, sixteen inches thick and weighs roughly 84,000 pounds. The entire project, designed by TLCD Architects and built by Jim Murphy Associates, comprises 120,000 square feet of sustainability and energy efficiency driven features.

It all started with a request from American AgCredit for a monumental rammed earth lobby wall that would express the relationship between agriculture and art. In October of 2013, this letter came into our office from Don Tomasi, Principle at TLCD Architecture in Santa Rosa, California:

I am the Principal-in-Charge for my firm for a new headquarters office building for American AgCredit, to be located in the Airport Business Park north of Santa Rosa. I am considering proposing a rammed earth wall at the main building entry, behind the reception desk. There is a potentially intriguing link between between my client's agricultural mission and an earthen wall, and I'd like to explore the possibilities with your firm if you are interested. 

My answer to Don, “Am I ever interested!”, but little did I know in October of 2013 where saying yes to TLCD, AgCredit, and an art wall adorning the reception area of an office tower was going to lead us.

Building a forty-foot long, twelve foot tall, 16” thick stabilized rammed earth wall comprised of multiple soil types is relatively straightforward for our team. After all, we have been building much bigger and more complicated wall systems for years. Our site-assembled and crane-set forming protocols are well established, as are volumetric mixing, conveyor delivery, and pneumatic compaction. In fact, we’re quite proud of all the cool things we’ve invented and built over the years that allow us to control consistency and wall quality on projects even larger than this one. 

I especially liked the idea of building a wall for American AgCredit, a bank whose sole mission is lending money to farmers. All of us at Rammed Earth Works appreciated the link between growing crops in earth and building a wall of earth in the lobby. The owners wanted us to incorporate soil from all of the regions served by the bank into the wall - Kansas, Oklahoma, Colorado, and across California. This wasn’t exactly practical, given the long hauls and budget constraints, but I did see how it was symbolic of the diversity of soil and agriculture. 

OK, so they wanted a rammed earth wall made up of multiple soil types, each yielding a different color and a slightly different texture. The wall was going to represent the reach of AgCredit, but we needed to create the pallet using soils that were close to the project site. Our color lab has gotten really good at developing mix designs from site soil and quarry crushings that conform to an architect’s color preferences, and by altering particle size gradations we can change the surface texture. I felt pretty safe saying we could meet their expectations on color and strata. 

The challenge for us in building the forty-ton rammed earth wall for American AgCredit was the fact that it was supposed to end up in the lobby. Because installing a traditional rammed earth wall requires a lot of space and equipment, we had to negotiate with the contractor to let us be one of the first subs on the site. The big footings that would be supporting the 2.8 million pounds of structural steel and 51,000 square feet of glass were the only part of the construction in our way when we set up.

It took us quite a few variations of samples and mockups to satisfy their aesthetic and symbolic criteria. We pulled materials from five different quarries - Calistoga, Santa Cruz, Glen Ellen, Byron, Napa, and a little red clay from Calaveras County - and three types of cement.

Estimating the materials and labor to actually build the wall? No problem. 600 square feet of double-sided formwork; 40 cubic yards of blended aggregate; 8.5% binder; two weeks to set forms, five days to ram, three days to strip and clean up; single mobilization, one or two call backs. 

But here’s the catch. Our wall was going to be in the center of a 120,000 square foot structure, surrounded by steel columns and concrete beams. In order for this to work we had to negotiate with the General Contractor to let us build our wall before any other structure was erected on the site. The GC agreed, so long as we would protect the wall from damage over the following two years of construction schedule. He squeezed us into the Gantt chart between footings and superstructure, which turned out to be not just a narrow window in time, but a window in space as well. They agreed to hold off on the steel frame until we were done, but they couldn’t hold off on digging footings. You may not realize how big a footing is for an office tower, but let me just say that it’s too big to step over, or to drive a bobcat or a high reach forklift over. Yes we had our little island in the center of the site to set our forms and build our wall, but getting to this island was a logistical nightmare. Everything took extra time, bridging, and required
equipment with a longer reach.

Long story short, we built the wall, they finished the building, it opened in March 2016 and went on to receive the 2016 AIA Redwood Empire Citation Award and the North Bay’s Top Projects Award. The building exceeds U.S. Green Building Council LEED requirements for Gold-level certification. Our rammed earth wall is the first thing you see stepping in the lobby.

What we learned:

  1. Building really cool rammed earth walls for display in high traffic commercial and retail spaces is a great way to showcase our work.
  2. Building really heavy rammed earth walls inside of another structure is complicated. Based on the success of the American AgCredit building, we knew that one day soon we were going to be asked to do another wall in a lobby, and when it happened, we needed to find a better way.

That day came sooner than we thought. In November of 2015, I received this letter from Justin Hughes of the SmithGroup:

Setting forms, and then filling them with all of the different soil layers, took only a few weeks. After our forms came down, however, we had to build a protective wall that remained in place for over two years while the building was finished, which meant we had to wait two years for everyone to see what it was we had accomplished. 

My name is Justin Hughes, and I’m an architect with SmithGroupJJR in San Francisco. We have just won a project to design a lobby for an office building in Santa Clara. We would like to use rammed earth as a 2-story feature wall as well as a floor material. We would like to discuss this with you, hear about your experience, understand some of the detailing as well as the possibilities and limitations of the material. The sooner we can meet, the better. If possible, we would love to have a meeting with your representatives and our project team in our office early next week, preferably Monday or Tuesday.

So here it was. The chance to innovate a whole new system - precast rammed earth. How could we manufacture big pieces of rammed earth thin and light enough to transport, yet strong and stiff enough to survive the bumps along the road? Could we engineer an assembly to mount these wall panels two stories high onto a structural back wall and would they stay there in a big California earthquake?

I said yes to Justin Hughes. I had to tell him we hadn’t done it before, but I knew figuring it out was going to be fun. I’ll tell you about it in the next few weeks.