151 North Franklin is an 807,000-square-foot, 35-story, Class A office tower located on the northeast corner of Randolph and Franklin Streets in Chicago. Each office floor features column-free lease spans, column-less glass corners and 9-foot, 6-inch floor-to-ceiling glass. The building is comprised of a steel structure surrounding a concrete core with concrete on metal deck, and utilizes low- and high-rise elevators. Designed by John Ronan Architects/Adamson Associates, its goal was to utilize high-performance architecture to support and attract companies.
One of its many standout features is its rooftop sky garden. It’s a beautifully landscaped outdoor top space exclusive to tenants that offers unique and unobstructed views of the windy city. It has high-altitude trees and plantings, and comfortable flexible seating suitable for entertaining or corporate events.
A Lasting Green Roof
Chicago-based American Hydrotech is a roofing and waterproofing company that offers single-source green roof and paver deck assemblies with the technical knowledge to install and maintain protected membrane roofs.
American Hydrotech worked closely with the design and construction teams to best implement its Garden Roof and Ultimate Assembly from the waterproofing membrane, insulation, and all the components of the hardscape and softscape. Data from its Hydrotech Hydrology Tool (HHT) generated “what-if” scenarios for engineers and designers looking for optimized garden roof assemblies to address the tower’s stormwater management needs. This project-specific information includes C-values, curve numbers, water storage amounts, and data on local storm events.
“Our goal was to help install a thriving and long-lasting green roof and amenity deck for tenants and faculty to enjoy,” says Jacob Soukup, digital marketing supervisor at American Hydrotech. “The green roof will act as a type of sponge to absorb stormwater during large rain events; it will help combat the urban heat island effect; it reintroduces biodiversity to the downtown environment and even includes a bee hive that is overseen by a local Chicago beekeeper. The amenity space provides tenants a chance to take a daytime breaks, gather for outdoor meetings and also hosts private events for the building, all while sporting amazing skyline views.”
Lake Zurich, Illinois-based All American Exterior Solutions was an installing contractor for the project. Its project manager, Nate Strawn, was heavily involved with the project early on by working on shop drawings, procuring material, and participating in weekly site visits and numerous coordination meetings. “It is definitely one of the projects I am most proud of in my career.”
Strawn notes Hydrotech’s Monolithic Membrane 6125-ED, a hot fluid-applied rubberized asphalt waterproofing/roofing membrane was used for the majority of the roof. “We had a root-stop root barrier below the green areas,” he says. “Then we had a drainage mat and two layers of Dow extruded polystyrene. And then from there, depending on the type of system, we had a garden drain, drainage mat or fabric. We used checker-block paver beneath the green on the main roof; a concrete cast reinforced grid [that offers high strength for wind ballasting] was strapped together in an array on the corners. This was required by the manufacturer for additional securement against wind uplift, while maintaining the project’s green roof square footage requirements.”
American Hydrotech’s Ipe Wood Tiles aided the appearance of the roof deck. These wood tiles are fabricated from very dense, durable hardwoods that exhibit excellent resistance to weather. The wood tiles can be periodically treated with oil to preserve and enhance their original color, or left untreated to develop a natural, aged finish. In addition to the roofing system, All American Exterior Solutions installed a vapor barrier, metal panels and expansion joints throughout the entire project. “We pretty much had our hands on the whole building,” Strawn adds.
The tower’s expansion joints required detailing at the adjacent parking garage. This consisted of a heavy-duty waterproofing membrane, Emseal expansion joint, and intricate sheet metal flashing. “It allowed for a continuous, compatible and watertight expansion joint that covered a gap of about three inches,” Strawn says. “Had the gap not been covered, eventually you would have rats, rodents and mold. They wanted to ensure it was watertight to prevent moisture from getting in there.”
Strawn calls the intensive green planter areas “a deeper green roof,” and it consists of both trees and plants. “The systems are all similar but the protection board changed to a non-root barrier at the paver areas,” he says.
Construction Sequence
The construction sequence was very thorough. Strawn says it was started with some temporary flashing throughout the project to make things watertight as pouring and construction were initiated. “Once we mobilized, we moved around a lot at the various levels. Level 35 had the sky garden roof. The main roof was level 36, and then we did the penthouse above the main roof. From there we began with the fluid-applied waterproofing. Once that was watertight, we moved to the next area, until we were ready for the overburden components, the insulation, the drainage, pavers, etc. Then we conducted tests for QA/QC prior to the insulation of the overburden: electronic leak detection.”
Once that was completed, the insulation and other components were installed and then the landscaper laid down the growth medium. Green sedum carpet, which also required additional wind uplift disk anchors, was rolled out too. “Our teams were setting pavers simultaneously and from there once the systems were installed there were various detailing and punch lists to be addressed” Strawn says.
Challenges and Safety
Navigating through downtown Chicago is no easy task, especially for semi-trucks. “We used smaller BOX trucks to unload from the loading dock, when we were able to,” Strawn says. “Additionally, a challenge was moving the equipment and material between various building levels. We loaded a significant amount of material with material hoists. Since there were no internal elevators yet, we had to ensure that the majority of the material and larger equipment was loaded prior to the material hoist coming down. So, it was a challenge to coordinate our deliveries and make sure we had it all up there before the material hoist came down.”
Rooftop safety is always a concern, especially with high rises. Strawn said fall protection was a number one priority for 151 North Franklin. “On this particular project, the GC handled the cable railing system and access for the material hoist. Once the cable railing system was installed, the fall hazard was significantly reduced. However, if guardrails are not provided, we do require 100% full-body harness tie-off. We have strict safety procedures to ensure everyone goes home uninjured at the end of the day.”
Garden Roof Coordination
What was unique about the coordination efforts for this garden roof? Strawn notes they had to make sure they were on schedule to allow the landscaper to come in and load the materials before the material hoist came down. “We also had to ensure the installation of the plants occurred after the majority of the all the work was completed to minimize damage to the plants,” he points out. “That’s one of the hardest things to do at a construction project — limit the damage to the plants because a lot of those other trades don’t care. They don’t understand. Just trying to coordinate when the material hoist comes down, you are kind of limited, but we tried to do the best we can to manage that. Any time you are working with other trades in a high-profile, high-rise project like this, the details can be very complex. So, there were many coordination meetings to ensure it could be built the way it was designed.”
151 North Franklin Awards
The roof and the building are a success. 151 North Franklin holds LEED Core & Shell Gold certification, WELL Core & Shell Gold certification, SmartScore Platinum certification, was Energy Star certified in 2020, and has been Wired Certified Platinum for 4 years. It also earned a WELL Health-Safety Rating, joining global industry leaders committed to implementing evidence-based strategies to address a post COVID-19 environment.
TEAM
Design Architect: John Ronan Architecture, Chicago, jrarch.com
Architect of Record: Adamson Associates Inc., Toronto, Ontario, Canada, adamson-associates.com
Construction Manager/General Contractor: Lend Lease, Chicago, lendlease.com/us
Roofing Contractor: All American Exterior Solutions, Lake Zurich, Illinois, aaexs.com
Landscape Contractor: Christy Webber Landscapes, Chicago, christywebber.com
MATERIALS
Membrane: MM6125 Hot Rubberized Asphalt Membrane, American Hydrotech Inc., hydrotechusa.com
Root Barrier: Root Stop, American Hydrotech Inc.
Drain Board: Gardendrain, American Hydrotech Inc.
Flashings: HydroSeal, American Hydrotech Inc.
Architectural Pavers: American Hydrotech Inc.
Ipe Wood Tiles: American Hydrotech Inc.
Insulation: DOW Polystyrene, DOW Chemical, dow.com
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