“Pavers could have been cut and trimmed to fit the patio’s shape and express the design, but not seamlessly,” Hill says. “It would not have been as visually appealing with all the lines in the patio from the paver pieces looking like a jigsaw puzzle.”
Pavers also presented another problem. With a permeable-paver system, the threshold between the patio and new doors to The Block would have been 4 inches. That threshold height would have been a tripping hazard.
So what paving material would work? Wierenga had used one in projects at grade that he thought might work. “I knew that it is lightweight, permeable, and pourable within forms to conform to the angles of the patio and give us the musical note pattern,” he recalls.
The material he recommended is available in two formulations: 50 percent recycled rubber chips and 50 percent stone aggregate with a moisture-cured binder or 100 percent recycled rubber chips with a more elastic binder. The manufacturer engineered the slip-resistant paving material for permeability with 29 percent void space. Water goes right through its surface, leaving no puddles of rainwater on the patio.
Mixed in a standard mortar mixer, it is ready to pour in just one minute. One inch of the all-rubber formulation, weighing just 3 pounds per square foot, was installed for the patio. This created a threshold of 1 1/2 inches.
Offsite, the manufacturer constructed forms in the shapes of the four musical notes in the patio design. Before pouring the paving material into the forms, employees coated the sides with vegetable oil so it would not adhere to the forms as it cured. On the rooftop, the notes were positioned in place, and the rest of the material was mixed and poured around the notes to complete the process. The three lines through the musical notes that contribute to the page of music design were poured into forms on the roof.
The installation achieved a smooth and seamless expression of the design. The gray and black custom-color mix harmonizes with the color of the new wall around the roof’s perimeter and complements the gray concrete elements of the Russell Block Building.
Installing any paving material atop a green roof’s geotextile protection fabric and drain sheet requires careful staging. Any sections of the geotexiles that extend out from underneath the installed paving material should not be left unanchored. Wind uplift under exposed edges of unsecured geotextiles can potentially lift and damage the paved surface. Wind uplift can easily be avoided if all the edges of geotexiles are secured.
The Block’s rooftop patio and garden is open an hour prior to each arts event. Patrons gather outside in the summer to enjoy the space and the view. Groups that rent the venue for special events also appreciate the green roof. As a testimonial to its beauty and appeal, couples choose the patio as a memorable setting for wedding photos.
“We had not previously used this pour-in-place, permeable-paving material on a rooftop,” Post notes. “Based on the results of the West Michigan Symphony project and the material’s performance over more than 15 months, we would recommend it and specify it again, especially in applications where light weight is an advantage because of load considerations.”
Architect and Landscape Architect: Fleis & VandenBrink Inc., Grand Rapids, Mich.
General Contractor and Roofing Contractor: Port City Construction & Development Services LLC, Muskegon, Mich.
Structural Engineer and Roofing Consultant: JDH Engineering Inc., Grandville, Mich.
Roofing/Waterproofing System: EverGuard Extreme TPO 70-mil Fleece-Back Single-Ply Membrane from GAF
Geotextiles: TerraTex Geotextile Fabric and TerraDrain 101 XL Geotextile Drain Sheet from Hanes Geo Components
Mixed Extensive and Semi-intensive Green Roof: Advanced Green Roof Flex-Built System from Advanced Green Architecture
Permeable Pavement: Porous Pave XLS from Porous Pave Inc.
PHOTOS: Porous Pave Inc.
David Aquilina, Strategic Storyteller, assisted in writing this article.
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