Curvilinear design challenges are addressed by window-wall technology.
The latest addition to Nashville’s downtown skyline, the 33-story, 386-ft.-tall JW Marriott Nashville hotel, greets guests with an elegant, undulating front entrance. Intricate fountains, sculptures, and artwork contribute to the aesthetic.
Owned by Turnberry & Associates, Aventura, FL, and conceptualized by design architect Arquitectonica, Miami, and architect of record, Smallwood, Reynolds, Stewart, Stewart (SRSS), Atlanta, the curvilinear design draws inspiration from the nearby Cumberland River, which weaves around the city, and by the rooftop curves of the adjacent Music City Center.
Other amenities include a full-service spa, heated rooftop pool and bar, state-of-the-art fitness center, two more restaurants and bars, and 77,000 sq. ft. of event facilities. The interior of the hotel was designed by Stonehill Taylor, New York, aligning with the inspiration and feel of the exterior façade design. By design, guests are treated to panoramic views of the city throughout the hotel.
Because of its unique shape and complex configuration, the size and scope of the project posed significant facade design challenges. The team worked with Custom Enclosure Solutions (CES), Cartersville, GA, and YKK AP America, Austell, GA, to design and install a custom façade system.
What looked like a simple, straightforward design was actually quite complex. While curtainwall was used on the podium level of the hotel, the architects chose window wall to achieve the desired curved look of the tower— rather than the more conventional choice of curtainwall.
While curtainwall is typically first thought of for high-rise applications, window wall offers advantages. Window wall is often able to meet the requirements of aesthetics, energy, and acoustical performance, flexibility, cost, and speed. Whereas curtain- wall is installed in front of the slab, window wall is a slab-to-slab application. This provides more control over thermal and acoustical performance, particularly in high-rise applications where energy performance and acoustics are valued. Additionally, a slab-edge cover can often provide a more modern, clean design, mimicking the look of curtainwall for a reasonable cost.
John McGill, manager of the project center at YKK AP America, recalled the initial stages of the project, “The overall shape and configuration of the building and the size and scope of it truly set it apart,” he said.
While examining the design for the hotel, YKK AP engineers identified a total of 25 different angles to create the desired elliptical shape with a continuously changing radius. The engineers customized one of its window-wall products, the YWW 50 TU thermally broken window-wall system, to fit the job. While the glass itself isn’t curved, the window wall was segmented to create the curve, and a slab-edge cover achieved the same look and feel as curtainwall.
The YKK AP team achieved the curvilinear design by using three custom mullions that fit within each of the angles, rather than creating 25 individual mullions for each angle. The key to integrating a slab-edge cover that continually changed with the custom mullions was to ensure that they hinged among themselves, creating a fluid line around the building.
In addition to solving the design challenge of the continuously changing radius, the YWW 50 TU system also allowed a pre-glazed option, so that all window-wall panels could be fabricated, assembled, and glazed in the shop, rather than on site. This solution met a design specification that required as much of the installation to be done from the inside of the building as possible. Not only did the pre-glazed system speed up the installation process, it improved the safety of the installation team by not requiring as much work to be done from the outside of the building.
The pre-glazed window wall ranged from 9 ft. tall on the lower floors to 15 ft. tall on the upper floors, and took approximately five days to install for each floor. As with nearly all high-rise developments, an exterior crane helped load the floors.
Meeting Energy Codes
Another challenge was meeting energy codes with floor-to-floor and wall-to-wall glass. With the YWW TU 50 window-wall system, the glass pane is set to the front for thermal performance, which is enhanced by the company’s MegaTherm thermal break. MegaTherm’s polyamide material is said to be stronger and have a higher melting point than PVC or polyurethane. Since its coefficient of thermal expansion is close to aluminum, the bond between it and the extrusion maintains structural integrity through a wide range of temperature fluctuations. Additionally, it also provides dual-finish capability and is designed to accommodate 1-in. glazing infill, or 1⁄4-in. infill using adapters, the manufacturer states.
Spandrel glass and vision glass were used to hide a large portion of the structure’s concrete walls that otherwise would have been exposed.
Viracon, Owatonna, MN, 1-in. insulating glass units were constructed with VE 1-2M for use on the podium level of the building. On the tower, a 1-in. insulating glass unit with VRE 1-38 with 44% exterior reflectance was used, and 1/4 in. VRE 1-38 was used for the roof.
One of the notable elements of the JW Marriott Nashville is the fine-dining restaurant projecting out from the 33rd floor of the glass tower. With floor-to-ceiling windows lining the restaurant, guests can dine with sweeping views of the city.
“That projection, square foot per square foot, is probably the most complicated structure that I’ve ever worked on in my life,” said Michael G. Murphy, AIA, LEED AP BD+C, and principal at Smallwood, Reynolds, Stewart, Stewart, of the mezzanine level and restaurant.
The coordination of intricacies such as drainage, conditioning, wind loads, the movable nature of some of the window systems, and the interface between the structure, glass, and aluminum panels below make the restaurant an impressive addition to the overall facade. All of those elements combined work to create an outdoor dining area staking a claim as one of Nashville’s dramatic spaces.
“The end result is a positive addition to the city of Nashville, and it will be well-received for years to come,” said Murphy.