American Hydrotech Has ASLA Green Roof Covered
Affiliated with the National Academy of Sciences, the group coordinates the release of peer-reviewed papers and workshops on transportation issues.

In 1997, 20 years after its founding and well before the still-fledgling green roof industry began developing, American Hydrotech saw that the future of roofing would include literal and figurative green building practices. Partnering with the German company ZinCo GmbH, the company introduced its Garden Roof® assembly roofing system to the American market, bringing to the roofing industry a lightweight assembly that allows landscape architects and other design professionals to turn virtually any flat or gently sloped roof into a vibrant, environmentally sensitive landscape. Since its introduction, the Garden Roof assembly has become an industry standard for intensive, semi-intensive, and extensive green roof applications, and has been used in dozens of green roofs across the country, including several that have received awards from Green Roofs for Healthy Cities.

ASLA green roof

Most recently, ASLA choose the Garden Roof assembly for the green roof landscape on its building in downtown Washington, D.C. The ASLA green roof demonstrates the environmental and aesthetic value of green roofs; encourages more widespread use of green roofs locally and nationally; and showcases the value landscape architects bring to green roof applications.

“We chose this assembly because of its stormwater management capabilities as well as its ability to improve the building’s energy efficiency,” Nancy Somerville, executive vice president and CEO of ASLA, said of ASLA’s decision to go with the Garden Roof assembly. “American Hydrotech lends a great deal of technical expertise to its projects and provides an outstanding warranty.”

Anatomy of the Garden Roof
The standard Garden Roof assembly consists of eight layers that—working from the roof deck up—include the roofing membrane, a protection course/root barrier, insulation/air barrier, water retention, drainage/water storage/aeration, filter fabric, soils, and, of course, the vegetation. To compliment the myriad positive environmental impacts of a green roof, the Roof Garden assembly includes several environmentally sensitive aspects throughout its layers. The Garden Roof system includes recycled materials at every possible point, ensuring it has a literal top-to-bottom positive environmental impact. Details of each layer include:

• Roof membrane—American Hydrotech uses a hot, fluid applied, rubberized asphalt produced with a minimum of 25 percent recycled content for the roof membrane. This layer is applied in two coats, with a sheet of fabric between each coat for a final thickness of 215 millimeters.
• Protection course/root barrier—for extensive green roofs, the assembly employs the Hydroflex 30—the company’s standard protection layer—and its Roof Stop product to keep roots from penetrating the waterproofing/roofing membrane. However, the assembly for intensive green roofs includes a heavier protection course/root barrier to protect areas that will be subject to high amounts of construction traffic, or where plants with deeper and more aggressive root structures will be planted.
• Insulation/air barrier—This layer uses Dow Styrofoam®, a CFC-free, closed cell polystyrene that is strong, moisture resistant, and maintains long-term insulation value. Use of this level is optional and depends on the thermal value requirements of the structure.
• Water retention—Depending on the type of vegetation used on the roof and the climate where the roof is installed, the assembly could include a moisture retention mat. In this case, the mat is composed of recycled, non-rotting polypropylene fibers stitched through a polyethylene sheet that is rolled over the root barrier of insulation/air layer.
• Drainage/water storage/aeration—This layer comes in a variety of profiles for use in extensive and intensive assemblies. They consist of lightweight panels made of 100 percent recycled polyethylene, molded into retention cups and drainage channels. The layer is designed to allow for the free drainage of excess water, while at the same time promoting irrigation through capillary action and evaporation into the soil/vegetation level.
• Filter Fabric—The filter fabric is made of non-rotting, nonwoven polypropylene fibers, is resistant to natural acids and alkalis, and is chemical neutral. The fabric is unrolled over the roof area to cover the drainage layer.
• Soils—Hydrotech employs lightweight engineered soils to provide stability for the plant root systems, while at the same time putting the least possible weight on the roof structure. The soil is also engineered to provide essential nutrients, water, and oxygen for the green roof plants.
• Vegetation—Hydrotech does not specify vegetation for the Garden Roof system. In fact, a wide variety of plants are suitable for green roofs. The selection of plants depends in large part on the building construction, the anticipated use of the green roof, and local climatic conditions.