Building Materials

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Success with Granite and Rainscreens

While open joint, or rainscreen, cladding systems have become an industry standard, many design teams overlook the opportunity of incorporating natural stone into the plan. These open joint systems gained popularity in recent years for their benefits to a building’s lifetime performance, with terracotta and metal comprising the most common selections for the cladding material. However, when an upscale finish or greater design freedom is desired, granite offers an ideal solution.

Stone can provide great performance with a rainscreen design, yet design teams often have many questions about how to incorporate them. Is granite too heavy for a rainscreen system? What kind of anchoring details are required? Will the stone panels remain secure? Can I be confident that a rainscreen with granite will remain low maintenance for years to come?

With today’s rainscreen cladding systems designed specifically to incorporate natural stone, granite can provide a long-lasting, beautiful option for building designs. By understanding the details of the systems, a team can confidently specify granite for a rainscreen.

Understanding Anchoring

When specifying stone for a rainscreen system, it’s important to understand the anchoring systems that work best with the building’s design. In a traditional cladding system for stone, anchors connect each cladding piece, and a 1- to 2-inch (2.54- to 5.08-cm) air gap lies between the cladding and the building.

When moisture builds up in the air gap, gravity pulls it down to the base course of the building, where channels weep the moisture toward the outside.

Rainscreen systems keep buildings moisture-free with their open joints that create a breathing, exterior skin for the building. Air transfers back and forth, eliminating the buildup of moisture or condensation between the cladding and the building.

One of the design team’s primary concerns with anchors for a rainscreen system is keeping them unexposed. To provide the seamless appearance of unexposed anchors with the strength required to securely hold granite in place in a rainscreen, the two most common hanging methods include a track-type system and a rebated kerf design.

The track-type system is perhaps the most widely used way of securing stone to a rainscreen system. A track system combines wall anchors to support kerf-cut thin stone and works essentially as a clip configuration that allows stone to be attached to an aluminum or stainless-steel rail with a Type 31 anchor.

Functioning like a tension anchor, the anchor in a track system remains hidden behind the stone and doesn’t sit in the kerf at the edge of the piece. The stone fabricator creates slots in the back of the stone pieces for the anchors to fit into. This allows joints to remain open and air to be transferred without visible anchors.

The second most common method of rainscreen anchoring is a rebated kerf design. In this design, an L-shaped cut is made in the edge of each stone piece to conceal the anchor.

In the following case studies, different types of rainscreen systems incorporate stone for a beautiful result various applications.

Wayne State Biosciences Center

In the world of higher education, buildings with inspiring designs play a key role in recruitment. When recruiting researchers, the stakes are even higher. The best and brightest in the field of research want a standout facility where they can collaborate, test and develop new technologies for the future. Creating such an environment was Wayne State University’s mission with its new biomedical research facility project.

The project architect desired a rainscreen cladding system for the large granite panels, which averaged 9 by 4 feet (2.74 by 1.22 m). The rainscreen protects the building’s exterior wall from rainwater by preventing it from penetrating the interior of the facility and lowers the risk of wall rot by allowing for drainage and evaporation. The rainscreen will also provide additional benefits such as ease of maintenance, thermal insulation and enhanced interior acoustic performance.

The $93-million Integrative Biosciences Center (IBio), was the culmination of years of planning and construction. Designed by Harley Ellis Devereaux of Southfield, Mich., the building encompasses 207,000 square feet (19,230 square meters) and is the largest construction project in Wayne State University’s history. The facility was designed to accommodate research activities for approximately 400 researchers and staff and more than 50 principal investigators and visiting scientists and scholars.

Multiple exterior finishes help create an eye-catching design for IBio. Approximately 9,000 square feet (836 square meters) of Mesabi Black® granite in a Diamond®100 finish from Coldspring was selected to clad the building’s southern face. Other materials such as glass and brick were used as well, representing a fusion of modern and traditional design.

“One of the important goals was to make sure the building stood out,” says Anne-Lee Vandenbussche, Director of Planning and Management, Wayne State University. “It’s the first WSU building you see driving down Woodward towards downtown Detroit.”

Both modern and traditional design elements were important for IBio’s design, as the building itself is a juxtaposition of existing and new construction. Covering one square block, the facility includes the repurposed space from a former historic 1927 auto dealership designed by renowned industrial architect Albert Kahn. The historic building was expanded with 78,000 square feet (7,246 square meters) of new construction.

“Granite as a material selection provides a nice connection between the existing and the new,” says Vandenbussche. “It’s considered a timeless product. Granite gives the appearance of a building with 50 to 80 years behind it, but it looks modern, too.”

Granite’s inherent durability is a good choice for universities, where ease of maintenance and the ability to stand the test of time are two important considerations. In addition, granite’s durability was enhanced by its incorporation into a rainscreen cladding system.

building exterior

Achieving success with the rainscreen required close coordination between the stone fabricator and supplier, Coldspring, and Gridworx, which designed the track-type hanging system needed to support the granite panels. Ultimately, Coldspring and Gridworx met the project’s requirements and schedule and satisfied the look the university and architect wanted. A team of Barton Malow /L. S. Brinker, Southfield, Mich., and Schiffer Mason Contractors of Holt, Mich., implemented the plan for a successful installation and completion of the rainscreen. Every team member involved from design to installation had to be engaged and precise to ensure the rainscreen was properly completed.

The LEED silver building is an important project for Wayne State University, as it enables the university to participate in the National Institutes of Health funding and initiatives. What’s more, Wayne State University played a key role in the economic revitalization of Mid-town Detroit by redeveloping 2.75 acres (1.11 hectares) of vacant real estate.

“Everyone loves this building and we get a lot of compliments on it,” says Vandenbussche. “We’re proud to be the gateway to the university from Detroit.”

Clad with a rainscreen system to prevent moisture and freeze-thaw damage, IBio will provide a beautiful, long-lasting solution for the students at Wayne State as well as the people of Detroit.

50 FIFTY

50 FIFTY

The 50 FIFTY building in Denver, Colo., provides a good example of a rainscreen cladding to create a modern aesthetic. 50 FIFTY is a 12-story tower of Class AAA office space — a designation it earns, in part, by its superior materials and finishes.

The 185,000 square-foot (17,187 square-meter) building consists of five full floors of parking, six floors of open office and one double-height lobby. The building’s elevated office floors have excellent views of the surrounding mountains, and it provides a visible landmark for travelers on the adjacent I-25 corridor. Building amenities include co-working spaces, a fitness facility, a roof deck, and a lobby with accommodation for both a financial institution and a café.

50 FIFTYBefitting the building’s prominent location, design excellence was a priority, and handpicked granite was one of the metrics for meeting quality and performance standards. In total, about 37,000 square feet (3,437 square meters) of granite was selected for the project. Sierra White® stone was selected for the building’s rainscreen cladding. The stone features a consistent appearance, and its light color fits well with the project inspiration of nautical themes. The Thermal finish delivered the slightly smooth texture the team desired.

Design elements were based on the owner’s passion for sailing. “Sierra White is representative of the whitewater break a sailing vessel makes as it cuts through the ocean,” explains Robin Ault, Director of Design and Principal, Clutch Design Studio.

Coldspring assisted with detailing and sampling various finishes of granite colors during the selection process. Members of the teams visited Coldspring’s California quarry, where they learned about plant processes and viewed the exact stone that would be used on the building.

“At the plant, we met with staff who provided a thorough education on the entire process, which was very well-received,” says Ault. The architects worked with curtain-wall subcontractor Harmon to develop a clip system for the rainscreen that integrated with their standard curtainwall system. Coldspring’s Mesabi Black® stone was also installed in the tower as a wall base to accentuate the building’s lightwells.

“For the landscape design, we thought about the importance of craftsmanship, such as you might find on a yacht, and we paid close attention to material fabrication and the interface between materials,” says Craig Vickers, Principal, Civitas Inc. Mesabi Black stone with Diamond® 10 finish was used for wall cladding, copings and stair treads.

50 FIFTYWhen polished, “Mesabi Black® has reflective qualities, resembling water, and where it is left unpolished, it has the stable look of earth,” says Vickers. “We didn’t want a monolithic feel for the site detailing that you might find at a courthouse or monument. Rather, we opted to detail the walls and steps in a way that would bring together multiple materials such as stainless-steel risers with granite treads and granite wall veneers combined with stainless steel and IPE wood seat decking. All were intended to capture that yacht level of craftsmanship.” The result was a finely crafted office building that will provide a stunning home for businesses in downtown Denver for generations to come. Success was made possible through superior collaboration among all members of the team.

Temple University Library

Located in Philadelphia at Temple University, Charles Library is one of the country’s most modern and significant new library constructions in recent history. Its design demonstrates the creative possibilities with granite and rainscreen systems and fulfills the architect’s intent to spur imagination and inspire excellence.

Key to the building’s striking design is more than 37,000 square feet (3,437 square meters) of Mesabi black granite from Coldspring, specified for exterior cladding, windowsills, soffits, coping, and a green roof wall façade.

Coldspring worked hand-in-hand with the architecture firm Snohetta of New York to meet the design intent. The architect visited Coldspring’s Mesabi Black® quarry in Babbitt, Minn., before the project’s start to view numerous mockups of the material and finish options. Throughout the process, close collaboration between Coldspring and the design team ensured the material’s natural characteristics and the color range associated with its various finish options were understood.

Vertical sections of the granite in a split-face finish clad the library’s solid base and coordinate with the existing campus landscape. A total of more than 30,000 square feet (2,787 square meters) of granite pieces – each featuring rustications or reveals – were successfully produced with manufacturing skill and quality.

“To keep the costs of the rusticated pieces within the owner’s budget, we evaluated our processes from the outset to develop production efficiencies,” says Duane Krueger, Regional Sales Manager for Coldspring.

The stone’s installation on a sealant-less, caulk-less rainscreen system allows for water drainage and evaporation, preventing water from penetrating the facility’s interior while lowering the risk of wall rot.

Each long, slender granite piece for the building’s cladding measures approximately 6 inches (15 cm) wide, 4 feet (1.22 meters) long and 2.25 inches (5.72 cm) deep, presenting a challenging installation for the contractor, Dan LePore & Sons Co. of Conshohocken, Pa. Because of the stones’ small size, they rely on two points of attachment rather than the typical four.

The team at Dan LePore & Sons laid out the rainscreen’s extruded, anodized aluminum grid system at their shop before delivering it to the site. Each aluminum rail measures 30 feet long.

“Plates mounted on the back of the stone engaged with the horizontal rails of grid system to form the mounting system,” says Greg LePore of Dan LePore & Sons. “Our skilled installation team then hung each piece along the building’s complex arcs and curves.”

Mesabi Black granite also provides a key design element for the building’s green roof, where it adorns the façade and coping. The dimensional, 2- by 2-foot (.61- by .61-meter) granite blocks provided challenging rigging, logistics and installation at the building’s parapet.

A beautiful outcome for a challenging design was accomplished at every stage of the project by the skilled, well-coordinated team. Today, Charles Library is a centerpiece of Temple University and the city of Philadelphia where its inspiring design promotes learning, innovation and community.

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