Grand America Hotel in Salt Lake City, Utah.

by M.W. Penn

Prefabricated panel systems are frequently used on buildings that require a flat veneer with little or no architectural detailing. However, some panel fabricators now have developed the capabilities to produce versatile, custom-engineered systems that allow even highly detailed stone facades to be panelized. With properly engineered panel systems, steps and setbacks can be incorporated, as well as heavy cubic elements such as pilasters and balustrades. The following article addresses many of the common concerns and questions about natural stone paneling.

What are the benefits of a panel system? BUDGET:
Because panel installations reduce not only the amount of scaffolding required but also the work schedule and size of the field crews, panel installations are often more cost effective than handset installations and field-framed substrates. Stone material costs could also be reduced as panel systems can allow for the incorporation of a thinner material. In addition to saving money, this can often reduce the overall building mass, achieving indirect savings on the structure. Additional efficiencies can often be identified when the stone contractor is involved in the design phase, allowing engineering enhancements to be thoroughly developed prior to the release of final construction documents.

SCHEDULE:
Because panel systems are constructed off site, often in a climate-controlled facility, weather conditions do not delay the fabrication schedule. Off site assembly also allows the panels to be fabricated simultaneous to the construction of the building structure. This allows the enclosure walls to be installed in less than half the time, enhancing the overall schedule and allowing interior finishing to begin at an earlier date.

Utah State Capitol Extension

QUALITY:
Plant assembly insures a rigid quality control program and allows the fabricator to follow a strict inspection schedule prior to on-site installation. Additionally, panel systems can be custom-engineered to meet a wide range of specifications, including seismic drift requirements, wind loads, and freeze tolerances. Weep systems can also be incorporated into the panel design.

Can the joint tolerances be tight? Will the panel joints visible?

	Nauvoo Temple detail.

A common misconception with panel systems is that there will be unsightly joints between panels. However, there are multiple options for blending panel joints with the field joints.

All large masonry walls, whether field set or panelized, require movement joints for thermal expansion and contraction. The size of these joints depends on several factors, including the lateral stiffness of the building, the joint material used, and the fabrication tolerance of the stone. On typical panel projects, joint sizes average 5/8" both within and between panels; however, based on the above factors, there are ways to reduce the joint size down to 1/2" or even 3/8" in some cases.

The difference in Joints within and between panels can be indistinguishable when a single joint material is used, and issues of movement and expansion joints are properly engineered. If all joints are sealant joints, rather than a mix of mortar and sealant, and the expansion and contraction characteristics allow expansion joints to match the typical joint size, then the panel system jointing blends.

Another critical condition to address when determining joint size is the amount of story drift from wind or seismic forces that will be allowed by the primary building structure. The stiffer the structure, the easier it is to achieve a smaller yet viable and less visible jointing pattern.

Panel assembly front and back.

It is also important to consider that panel joints do not necessarily have to be straight vertical joints. Stepped or toothed panels that zigzag according to ashlar running bond coursing can have field placed stones engineered to span separate panels so there are no interruptions in the pattern. Running bond joint patterns with no field placed stones, while more difficult, are also possible. If the entire building does not lend itself to panelization, there are ways to combine the panelized portions of any building with hand set portions, creating a seamless application.

How do panels address corner joints?

	Panel assembly in plant.

Corner joints can be treated in several different ways, depending on the building design. For many designs, a quirk-mitered joint works well and allows some movement at this critical location. If the corners are designed to express the veneer thickness, that is if the edge of the stone is visible on the adjacent wall face in a toothed corner, a movement joint can be provided following the toothed pattern. If the corners have large returns or quoins, the veneer can be fabricated to give the appearance of thicker stones and a joint may be worked around the toothed quoins.

Can panels be used for a radial design?
It is possible to fabricate radial, or curved, panels. This is accomplished by constructing a radial truss and attaching thicker stones that have been fabricated to the true radius to that truss. The feasibility of this method is dependent on the size and detailing of the stone and the chosen framing system of the panel.

Some Stunning Examples by KEPCO+
KEPCO+ has been in the cladding industry for twenty years and specializes in the design and installation of panelized natural stone, tile, and terra cotta cladding systems. The company has had great success utilizing panel systems on both new construction and renovation projects. On some projects KEPCO+ partners with Dee Brown Inc. via KEPCO+DBI.

Walt Disney Company Headquarters

Walt Disney Company Headquarters
When the Walt Disney Company initiated plans for their corporate headquarters in Burbank, California, they knew they wanted to portray the company's strength and firm foundation through the use of natural stone. The impressive two to seven story headquarters building was designed by architect Michael Graves in Indian Red Baruli Sandstone.

To keep the project on schedule, Kepco+ pre-assembled panels for a significant portion of the exterior cladding. The panelized elevations were designed to match the handset portion in both the 3/8 inch joint sizes and the nature of the cleft surface material. In this instance, the use of custom panels enhanced the completion schedule of the building.

The Nauvoo Temple

The Nauvoo Temple
A historically accurate re-creation of a temple destroyed over a century ago, the Nauvoo Temple in Nauvoo, Illinois, was completed by KEPCO+DBI in 2002. The limestone-clad temple incorporates 100 massive stone carvings as well as six different hand-tooled finishes, mimicking even to the smallest detail its 19th century predecessor.

The project was designed as a traditional gravity-stacked masonry project with concrete sheer walls, yet the construction schedule did not allow time for a complete handset application of the limestone. Additionally, the project owner specified that the project should exceed standard code requirements and all attachments should be stainless steel. To meet the strict schedule while also adhering to all quality requirements, KEPCO+ proposed that 80% of the project be panelized.

However, because most panel systems are designed with gravity load supported by the structure at each floor, a traditional steel framing method was not feasible. Instead, stainless steel strong-backs were designed to transfer the load down to the foundation, mimicking traditional, gravity stacked masonry and using only lateral connections to anchor the panels. The unique panel system was not only cost effective, but also provided better long term technical performance and enhanced the overall project schedule.

Utah State Capitol Extension

	Utah State Capitol Extension

One of Salt Lake City's most notable landmarks, the classically designed Utah State Capitol is clad with granite from Salt Lake's Little Cottonwood Canyon. When two buildings were needed to meet the growing needs of state government and to provide space for the Capitol building occupants during a seismic upgrade and restoration of the existing historic capitol building, several criteria had to be met. It was important to use a compatible stone to give the new buildings the richness and classic beauty of the older building. Intricate stone detailing similar to the dramatic classical façade of the existing structure had to be incorporated into the design of the new structures. Attachment of the stone to the building structure had to satisfy force and displacement required by code for high seismic risk zones. And it was important to meet the time demands necessitated by the already scheduled work on the older building.

Through a successful design-build effort, KEPCO+ DBI was able to overcome all these fabrication and installation challenges during the design period. The positive outcome is evident in the two new government structures and their contribution to the beauty of the overall complex.

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