Vermont slate meets historic and environmental requirements
Originally built as Fort Saint Anthony in the 1820s, Fort Snelling is spread across 300 acres in St. Paul, MN, and is strategically situated at the confluence of the Minnesota and Mississippi rivers. Today, the Minnesota Historical Society runs the fort, which is located atop a bluff along the Mississippi River. The Northern Star Council for the Boy Scouts of America, which serves communities across central Minnesota and western Wisconsin, believed it was fitting to expand its headquarters there.
The $17 million expansion included the addition of the Peter J. King Family Foundation Leadership Center. The new building features an atrium, welcome area, expanded retail shop, interactive technology room for kids, several meeting rooms, a climbing tower and a team-focused high ropeschallenge course. The Council also moved its two offices in St. Paul and Golden Valley into the center.
As the design and construction team, the concerted effort of Cuningham Group Architecture Inc., Mortenson Construction and the Vermont Slate Company, set out to make the Council’s vision a reality. For starters, they had to be sensitive to what materials were used in the process because the project sat within a historic district, thereby limiting what would be consistent with the building context. In addition, because Minnesota is known for its extreme climate, they needed a wall system and cladding that was able to withstand the large temperature swings. “They wanted the environmental benefits and efficiency of a ventilated rain screen, the look of a natural product, the 100-plus-year durability of natural slate with virtually no maintenance and a price that was competitive with other rain screen systems,” said Ken Rule, owner of Vermont slate.
Natural slate also has historical value as a cladding material. For thousands of years, slate roofing has been used on castles, cathedrals and homes for both roofing and cladding. Revered for being a durable and long-lasting material, the material is capable of withstanding shock from hail, acid rain and even hurricane-force winds without breaking. On average, a quality slate roof has an expected lifespan of more than 100 years but have survived as long as 500 years on some European Castles. Installed as cladding, the life expectany can be even more. As an added bonus, the minimal processing of natural slate makes it one of the most environmentally friendly building materials on the market. “The slate contributed to the overall aesthetic with its modern metallic luster, and yet was a modest complement to the historic 1913 Calvary building that sits adjacent to the BSA leadership center,” said Chad Clow, AIA, NCARB, principal at Cuningham Group Architecture. “The wall system concept and slate exterior detailing provided the performance that we required.”
The decision was made to use Spanish Slate with high-quality control and the ability to remain colorfast for more than a century. The material is highly reflective, adding to its aesthetic value. The job required 15,000 square feet of 16- x 8-inch slate pieces, totaling about 23,000 pieces, with every piece hand split in the factory.
Attaching the slate
While the project team decided on having a natural slate facade, one of the difficulties they ran into was finding a way to install it in a ventilated rain screen system. What was decided on is CupaClad, which is privately marketed and distributed by the Vermont Slate Co. in the U.S. CupaClad is a complete ventilated facade natural slate system combining highly durable structural natural slates with the efficiency of ventilated cladding systems. “There were several challenges [faced during the designing and building process],” said Rule. “First, since no one in Minneapolis had ever installed CupaClad; finding a sub-contractor to install it was difficult. In fact, after a training session at Mortenson to show them how it installs, Mortenson ran the numbers and decided to use their own union carpenters to put it on. In the end, David Wood, the project manager for Mortenson, said they were extremely happy with the results and felt like they had not only saved the project owners money by doing so, but also created extra in-house revenue and profit on the job. The second challenge was in the engineering. The CupaClad system had to meet some very high wind loads for this class of construction. The installation system was designed and quoted to attach to every other metal stud. This was a great idea on saving cost, but not such a great idea when the wind loads were applied. The result was a change to cut the vertical profiles down from 18 feet to about 6 feet and create a skip pattern for the back-up wall attachments in the high-wind load areas.
“It added some brackets to the system and some time for Mortenson, but it was not significant in the end since the overall cost was still less than expected,” Rule went onto say. “The nice thing was that Mortenson’s people did not get excited over a last minute change up and dealt with it very effectively and efficiently.”
The Center, named in honor of the King foundation’s $4 million gift in Northern Star’s capital campaign, opened in the summer of 2018, helping usher in a renewed commitment to the positive influence the Council makes in the lives of the 25-plus communities it serves. “Everyone is very pleased with the installation,” said Rule. “The material works well with other surfacing materials like wood and brick. Clients will definitely be specifying it again in the future.”