Vegetative Roof Waterproofing for Long-term Performance: 850 Third Avenue, New York, NY

by Brian Kelly

This 17th story vegetative landscape in Manhattan was designed to suggest a rolling meadow. [CREDIT] Photos © C. Taylor Crothers

This 17th story vegetative landscape in Manhattan was designed to suggest a rolling meadow. Photos © C. Taylor Crothers

Challenge
The goal of the 850 Third Avenue project was to install a green roof terrace above occupied commercial space to maximize property value while providing a pleasant enclave for Shorenstein Properties’ new commercial tenants. The approximately 789-m2 (8500-sf) rooftop area is set back over occupied space on the 17th floor and overlooks open spaces at a cancer center next door and a nearby Marriott Courtyard. A durable, watertight seal that could waterproof across the mixed-use, high-end design and offer an extended service life was essential. Odor-free application was also a prime consideration due to proximity of tenants and neighbors.

The design-to-installation cycle was shorter than normal, because the space next to the new terrace was unoccupied only temporarily until new tenants were booked to arrive. There were also issues with the capacity of the roof deck on the initial landscape design that needed to be addressed.

Solution
The project was designed in the fall and constructed in the spring of 2011. BOCA Group project engineers specified I-beam supports beneath plant beds to spread the load over the metal decking, clad with mechanically fastened cement board.

An ‘odor-free’ two-part polyurethane resin membrane system was specified for monolithic waterproofing protection beneath the varied landscape. The fleece-reinforced liquid-applied membrane fully adheres to the roof deck, up-sloped curbs, and around penetrations and drainage areas.

Beyond the natural appeal of landscaped roofs, special features can pose a tempting diversion.

Beyond the natural appeal of landscaped roofs, special features can pose a tempting diversion.

The final landscape design by Aaron Booher of HM White in New York suggests a rolling meadow and incorporates walkways, seating, and continuous veneer beds. Some are 457 mm (18 in.) deep and set with witch hazel and crabapple trees. The undulating meadow effect is created by strips of insulation board inside the base of the field planters.

“We used several palettes with seasonal flowers that bloom across seasons, including native cultivars. The effect, woven together provides textural relief across the landscape design,” Booher said.

Most beds are 102 to 152 mm (4 to 6 in.) deep and include grasses and perennials, with a few deeper wells positioned over structural supports. On the south side of the building, there is an extensive planting of sedums in 102-mm planters that drink in the sunshine. Planters are drip irrigated from below, and any excess rainwater not absorbed by the plantings and overburden filters to drainage mats and is channeled to the existing building drains.

To read the full article, “Vegetative Roof Waterproofing for Long-term Performance,” click here.

To read the sidebar, “Vegetative Roof Waterproofing for Long-term Performance: Two Types of Green Roof Assemblies with Waterproofing Membrane Systems,” click here.

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