A Dynamic Rooftop Renovation Lures a New Type of Workforce

Commercial office properties have always had to contend for tenants as a part of doing business and, increasingly, existing buildings are facing stiffer competition from new office properties offering integrated amenities packages that go way beyond the lobby coffee shop. As a new generation of employees enters the workforce, employers are challenged to secure leases that provide more than simple office space, instead offering an attractive combination of recreation, retail and relaxation options that feel more akin to a resort than a workplace. In the case of Prudential Plaza, a 41-story structure in Chicago built in 1955, the challenge for the building owners was to offer new value in a building originally designed to respond to a workforce that no longer exists.

The rooftop transformation is highlighted by a fully wired amphitheater, fire-pit lounge and a small lawn accompanied by a new 12,000-square-foot fitness center and a 7,000-square-foot clubhouse located inside.

The rooftop transformation is highlighted by a fully wired amphitheater, fire-pit lounge and a small lawn accompanied by a new 12,000-square-foot fitness center and a 7,000-square-foot clubhouse located inside.


Investing more than $85 million into building renovations, Prudential Plaza’s owners envisioned a top-to-bottom rehabilitation, crowned by a 13,000-square-foot amenities deck on the 11th floor. The rooftop transformation is highlighted by a fully wired amphitheater, fire-pit lounge and a small lawn accompanied by a new 12,000-square-foot fitness center and a 7,000-square-foot clubhouse located inside. These amenities are exclusively for building tenants and their employees. Kyle Kamin, a Los Angeles-based CBRE Inc. executive vice president and tenant broker who has clients in Prudential Plaza called the roof deck “a game-changer with an unbeatable view.”

Engineering

Certainly the idea of a gorgeous tenant recreation and lounge area would appeal to most; however, few outside of the design and construction industry would appreciate the immense challenge of adding this type of space on top of a 60-year-old roof. When Wolff Landscape Architecture, Chicago, was asked to partner with Chicago-based architecture firm Solomon Cordwell Buenz for landscape design, project manager Ishmael Joya quickly understood the complexities of the situation. Joya is a landscape architect with 15 years’ experience, specializing in green-roof construction.

“Prudential Plaza is a classic figure in Chicago’s skyline and the first time we walked the project it was clear that the 4 1/2-inch-thick roof deck was going to present some design and construction challenges,” Joya remarks. Although the Wolff Landscape Architecture team has completed many green-roof projects, including renovations, Joya realized that adding what is essentially a mini-park to a very thin structural surface was going to require out-of-the-box thinking. “In any roof-deck renovation, it’s critical to reduce the weight of the building materials because the building is only designed to support a maximum amount of weight and that can’t be compromised,” he says.

Joya worked closely with the design team’s structural engineer, Wiss, Janney, Elstner Associates Inc., Chicago, to make sure the appropriate products were specified to support the expected weight of each area of the renovation

Demolition and Interim Roof

Like many large-scale occupied renovation projects, Prudential Plaza’s overall renovation was executed in multiple phases, allowing construction activities to take place while tenants maintained their typical routines. Romeoville, Ill.-based Preservation Services Inc., a commercial roofing company, was responsible for rehabilitating the original 11th-floor roofing structure. The original roof was a modified bitumen membrane that had been applied directly to a layer of lightweight concrete and covered by 2- by 2-foot pavers. Preservation Services carefully removed the pavers, old membrane and thin layer of concrete.

Investing more than $85 million into building renovations, Prudential Plaza’s owners envisioned a top-to-bottom rehabilitation, crowned by a 13,000-square-foot amenities deck on the 11th floor.

Investing more than $85 million into building renovations, Prudential Plaza’s owners envisioned a top-to-bottom rehabilitation, crowned by a 13,000-square-foot amenities deck on the 11th floor.

Because the building is located adjacent to a series of vaulted streets, the construction team was unable to use a high-reach crane because the weight of the crane would have required special provisions and necessitated street closures. Consequently, crews carried all removed debris down through the freight elevators during the night while the building was largely empty. At the end of each night, a single-ply EPDM membrane was rolled out, seamed and secured to protect the under structure from possible water penetration the next day.

Once demolition was complete, the EPDM was opened in select areas so repairs to the concrete slab could be made by other trades. When repairs were complete, a single layer of torch-applied modified bitumen membrane was applied to the deck along with additional structural steel required to support the added weight of trees, planters, patios and people. Finally, a white, granular-surfaced modified bitumen roof over tapered isocyanurate foam insulation was installed making the undersurface ready for the plaza deck renovation work.

Weight Considerations

Joya recommended a lightweight expanded polystyrene (EPS) material with high compressive strength that is used to reduce axial loading on structures. He has found the product very easy to work with, which saves time and money, ultimately allowing designers to put more of the client’s investment into tangible value users will see and feel rather than subsurface building materials.

On the Prudential Plaza roof-deck renovation, two types of EPS were used. EPS 15 was used in areas that would largely be filled with plants and wouldn’t bear much foot traffic. EPS 46, chosen for its high compressive strength, was used as a structural fill across the design’s many grade changes and in areas that would bear more weight of roof-deck occupants. For Joya, another advantage of using the EPS is being able to see the shape of the assembled product and make any required changes before the concrete is poured and work becomes significantly more complicated.

PHOTOS: Wolff Landscape Architecture

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Today’s Roofs Provide Additional Square Footage for Developers and Owners

How much traffic can a roof system bear? The fact is, live loads on roofs are getting much bigger as building developers and owners seek to allow more indoor-outdoor uses and rooftop amenities, such as seating areas, gardens and even fire pits and pools, which draw people to the roof. Plus, the dead load may be increasing thanks to those living material installations, such as planters and vegetative roof gardens. These assemblies usually require or hold water—adding to the dead load—as well as frequent maintenance and inspections, which mean a few more people (and more live load).

Muzeiko, a 35,000-square-foot LEED Gold children’s science discovery center in Sofia, Bulgaria, includes a rooftop science play area with a lush green roof, climbing wall, rain garden, outdoor activity space and an amphitheater. PHOTO: ROLAND HALBE, COURTESY LEE H. SKOLNICK ARCHITECTURE + DESIGN PARTNERSHIP

Muzeiko, a 35,000-square-foot LEED Gold children’s science discovery center in Sofia, Bulgaria, includes a rooftop science play area with a lush green roof, climbing wall, rain garden, outdoor activity space and an amphitheater. PHOTO: ROLAND HALBE, COURTESY LEE H. SKOLNICK ARCHITECTURE + DESIGN PARTNERSHIP


“We’ve known the benefits of a green roof from a water-management point of view for some time,” says Joshua Zinder, AIA, principal of JZA+D, Princeton, N.J., noting that more than 70 percent of the water that hits the roof is absorbed. “Increasingly, we see the roof as an opportunity for generating revenue or enhancing the value of the building. One of the ways we’re now helping developers reposition older office and industrial properties is by determining if we can create roof farms or indoor-outdoor spaces not only on the ground floor, but also on the roof planes.”

The case of the rooftop garden with public access is a growing trend, too, and “one must ensure that the roof structure has the necessary structural capacity to support rooftop activity,” notes Kelly Luckett, author of Green Roof Construction and Maintenance. Local codes vary for live loads and dead loads, he explains, and the project team calculates the green roof assembly as part of the total dead load. “Water in excess of that which saturates the growth media, snow and people visiting the green roof are all considered part of the live load of the structure,” Luckett adds.

Just as important, the roofing system has to resist the wear and tear of the live loading. The three main concerns for exposed structural elements, such as roofs, balconies and terraces, are protection from weathering, water ingress and environmental damage. Pedestrian walkways must also ensure long-term durability.

A look at the latest trends in “activating rooftops” reveals even more reasons for roofing contractors, architects and facility owners to look more carefully at specification documents and installation methods for these live-load roof zones.

A new Department of Sanitation complex in New York City, designed by Dattner Architects with WXY Architecture + Urban Design, both of New York, features a dynamic façade of moving metal fins and a 1.5-acre planted roof, which contribute to the LEED Gold operations. PHOTO: WADE ZIMMERMAN, COURTESY WXY ARCHITECTURE + URBAN DESIGN

A new Department of Sanitation complex in New York City, designed by Dattner Architects with WXY Architecture + Urban Design, both of New York, features a dynamic façade of moving metal fins and a 1.5-acre planted roof, which contribute to the LEED Gold operations. PHOTO: WADE ZIMMERMAN, COURTESY WXY ARCHITECTURE + URBAN DESIGN

Skylife and Community

For residential projects with rooftop terraces, careful specifying and installation of green roof assemblies is critical. “We like using liquid membrane roof and extensive green-roof systems, such as sedum carpet,” says Andrew Franz, AIA, LEED AP, principal of Andrew Franz Architect PLLC, New York, adding that the systems work well because the drainage mat is modular, lightweight, and easy to install and adjust—something that is important on uniquely shaped urban rooftop terraces.

Recent projects by Franz include a 2,800-square-foot garden terrace for a family of four in Manhattan. A bluestone floor extends from the dining area to the terrace’s softscape herb garden, further blurring the boundary between in-doors and out. “The green roofing system also includes a protection mat, which protects the roof membrane, a filter sheet of very lightweight soil to protect the drainage mat and the sedum carpet,” Franz says.

Other recent projects with active green roofs demonstrate the benefits of strong PVC membranes, such as at the modern 93 Bright Street townhouse in Jersey City, N.J., designed and developed by Jorge Mastropietro, AIA, whose firm JMA is based in New York City’s Soho neighborhood. Another example, called Trouthouse, designed and built by the Brooklyn-based thread collective, is a showcase of “passive design” principles that reduce energy use, recapture water and even allow for a roof-mounted shade structure that doubles as photovoltaic panels.

The new LEED Gold-certified facility for Gateway Community College in New Haven, Conn., was designed with a vegetative roof to create a new community area on the top floor. According to construction manager Providence, R.I.-based Dimeo Construction, which worked with Providence-based Gilbane Building Co. and the New York office of architect Perkins+Will on the project, the “multi-level student gathering area steps up from the ground floor to a rooftop garden. The green roof also supports photovoltaic panels on a special framing system.”

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