Private Rooftop Garden ‘Lifted’ to New Heights with Geofoam
Written by Let It Grow
Meet Front and York, Brooklyn’s latest residential community at the base of the Brooklyn Bridge in the heart of DUMBO. The project is being developed by CIM Group whom have put together a renowned project team including celebrated New York Architect Morris Adjmi and landscape architect Michael Van Valkenburg Associates. The development will house luxury condominiums and ground-level businesses, such as the high-end fitness center, Life Time Fitness.
DUMBO, Brooklyn is known for its extravagance, however Front and York has taken that to a new level. The development features a 25,000 square feet private rooftop park at its core, an 8th floor courtyard, coffee house, media center, party lounges, children’s play area, pool, outdoor grilling areas and fireplace and even a wine room. This luxury residential community seems more like a 5-star hotel.
Let it Grow Inc. was excited to join the construction team in 2019, lead and managed by New Line Structures, to build the landscape architectural components of the private rooftop park. Our multi-trade capabilities, extensive experience constructing rooftop gardens and relationship with New Line Structures made Front and York a perfect fit for our organization. Our scope of work included concrete finishes, hardscape, site furnishings, planting, horticultural soils, carpentry, metal fabrication, plantings, green roof components, and of course, the installation of Geofoam.
The Rooftop Profile
The private rooftop park stands out from the traditional intensive green roof build-up due to the overall depth of the rooftop profile, the change in elevation from the buildings structural roof slab to finished grade where people walk and plants grow. This profile is 14ft at its maximum depth and consist of horticultural soils and pavements installed over geofoam fill. Geofoam was used across the park as structural fill to support the rooftop garden and finishes. The intensive green roof profile ranges from 1ft to 12ft in total depth with 2ft of growing media on top to support plant growth. Isolated pockets of deeper growing media were designed to sustain the growth of trees. In lieu of manufactured lightweight growing media, the design called for a traditional soil profile with three soil horizons; base sand layer (6-8” thick), horticultural soil root zone (12” thick) and top layer consisting of horticultural soils mixed with compost (6-8” thick).
What is Geofoam?
Geofoam is a lightweight, extremely durable material that is commonly used in the construction industry for structural fill and geotechnical uses. Geofoam was created in the 1950s and first implemented in construction in the United States in 1989 on State Highway 160 in Colorado. Since then geofoam has been utilized on thousands of construction projects all over the world and more recently on green roof projects. Geofoam is similar to Styrofoam but made up of polystyrene polymers. The main difference between Geofoam and Styrofoam is the manufacturing process. Geofoam is made through a process called polymerization where polystyrene resin “beads” are fed into a hopper and heat and pressure are applied within a mold. Depending on the mold and the amount of heat and pressure used, different shapes and densities of Geofoam can be made to meet various engineering needs. In the case of Front and York, an expanded polystyrene (EPS) Geofoam was utilized.
The Landscape Architect utilized Geofoam on the project as a lightweight structural fill to reduce the overall dead load on the building structure. Traditional soil fill weighs 110-120 pounds per cubic foot, whereas Geofoam only weighs about 0.9 to 2.40 pounds per cubic foot, significantly reducing the dead load on the building structure and providing a feasible solution to the elevation change that had to be addressed on the project.
The project requires the installation of approximately 23,000 square feet of Geofoam with multiple lifts of 4’x8’x12” Geofoam blocks ranging from 8” depth to 68” depth. Two types of Geofoam were used; 15 psi under walkways and trees and 3.6 psi under all remaining panting areas, adding up to over 1,500 pieces of Geofoam. The Geofoam for this project was manufactured by Shelter Enterprise in New York and delivered to the jobsite on numerous tractor trailers.
Rooftop Drainage is Essential
With such a high buildup of Geofoam on the roof, Let It Grow had to make sure rooftop drainage was installed properly in coordination with the Geofoam. The project’s landscape architect understood the essential need for adequate storm water drainage on this rooftop project, designing an extensive network of drainage measures in conjunction with the geofoam substrate. The design included 4 layers of drainage mat within the overall roof profile, horizontal drainage linked to a network of 60-80 drywells and a sand soil horizon below the horticultural soils. Large 3ft diameter access manholes were installed thru the foam to provide access to roof drains at the structural deck for routine maintenance, inspection and repairs to the roof drains if needed in the future. All of these drainage measures allow adequate storm water to infiltrate the soils to support plant growth while ensuring excessive storm water does not collect within the overall roof profile.
Plan- Execute- Deliver
Leave it to Let It Grow, Inc. to plan, execute and delivery the complex construction of Front and York’s green roof starting from the roof slab up. Planning involved the preparation of a comprehensive set of Geofoam shop drawings to ensure the various lifts of foam were well coordinated and laid out to follow the complex geometry of walks and contours of the proposed grading. In addition to detailed sections, each lift and individual piece of foam was shown over 45 pages of shop drawings. These shop drawings served as a blueprint for our field construction personnel to improve ease of installation and ensure the correct roof profiles were achieved
The internal courtyard location and heavy amount of overall construction being performed on the building presented a tight jobsite. Let it Grow developed a site logistics plan to allow large quantities of Geofoam to be transported to the roof and maximize productivity. All Geofoam was moved thru the building by skid steer to the roof where each piece was moved by hand. A majority of the Geofoam blocks needed to be cut precisely with a hot wire to ensure a proper fit.
Let it Grow is capturing the installation of Geofoam and overall project with their very own time-lapsed camera that overlooks the interior courtyard. The Geofoam installation is scheduled to be completed over 30 days this fall, while substantial completion of the project will be delivered by Let It Grow in the Spring of 2021.
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