The home features stacked stone and wood, natural materials that complement the landscape. To take advantage of the setting, large windows across the full length of the home look out toward the southern vista over the lake. From west-facing windows, the homeowners and their guests also enjoy views of the adjacent rock face and sunsets over the mountains.
A Steep Challenge, a Green Answer
Totaling 6,700 square feet, and measuring 40-feet by 150-feet, the home is large and long yet fits seamlessly into the site. The lot on which the home is situated is narrow and steep, dropping down from the road to the lake. “With local covenants mandating set-backs from both the road and the water, we had to design the house to make its way down the site from the road in order to have the square footage our client wanted,” said Platt.
The floor of the house sits 20 feet below the road. Thus, the top of the roof is level with the road, and the long roofline is visible from the road and driveway. Inspired by the site’s natural beauty, Platt envisioned that from the road a view of a green roof, instead of an unadorned rooftop, would help blend the home into the site.
Double decks on the steep slope. Photo Courtesy of Platt Architecture.
“A green roof would extend the natural landscape at eye level from the road out toward the lake,” said Platt. “It would be a natural feature that would serve the desired unification of the house with its setting.”
Relying on Green Roof Experts
Platt turned to Emilio Ancaya, GRP, co-founder of Living Roofs, Inc. Founded in 2006 and based in Asheville, N.C., Living Roofs, Inc. is the first company in North Carolina to specialize in professional green roof services. They provide green roof planning, design, installation and maintenance.
From the road above, the green roof integrates the home into the landscape.
Courtesy of Platt Architecture.
Roof slope angle is an important design factor in any green roof project. Roofs sloped from 10 to 45 degrees require green roofs with more depth and specialized components to retain and stabilize the growing medium layer against erosion and slippage. Accordingly, the 3:12 slope of the roof on the Lake Toxaway house was a basic aspect of the project that had to be considered in selecting a green roof system and planning the installation.
“We needed a system that would accommodate the slope,” said Ancaya. “In addition, I wanted a system and plants that would do well in the cool, wet mountain climate up at the 3,000-foot elevation of Lake Toxaway. Plus, we needed an instant green roof that would have extensive vegetative coverage on the day of installation. I just did not think the architect or homeowners would go for a system installed with exposed growing medium and take several seasons to fill in and green up.”
Slope stabilization grid ready for the growing medium.
June, 2013. The green roof complements the exterior’s natural materials.
Photos Courtesy of Living Roofs, Inc.
From the start of the planning process, Ancaya discussed the requirements with Clayton Rugh, Ph.D., general manager and technical director of Xero Flor America. Founded in 2002 and headquartered in Durham, N.C., Xero Flor America is the exclusive U.S. distributor for the Xero Flor Green Roof System.
“Living Roofs, Inc. has done many projects with Xero Flor,” said Ancaya. “I knew they had experience integrating slope stabilization into their system.”
Green Roof System Selection
The Xero Flor Green Roof System is an extensive system that utilizes pre-vegetated mat technology engineered in Germany and improved over the course of 40 years of ongoing research and development. It has been proven in Europe and around the world on tens of thousands of rooftops that cover hundreds of millions of square feet. In Xero Flor mats, the plants are pre-grown in an engineered growing medium on a flexible geosynthetic composite material, thermally bonded to a non-woven filter fabric reinforced with a layer of non-woven fleece. The mats are transported and delivered in rolls, much like sod. Installers roll them out across rooftops for easy installation.
Courtesy of Living Roofs, Inc.
In addition to the mats, delivered with extensive vegetative coverage with plants that are mature and thriving, Xero Flor green roof assemblies include one or more additional inches of growing medium (which supplements the growing medium integrated into the mats themselves), a retention fleece, a drain mat, and a root barrier.
Positioned atop a roof’s waterproof membrane, the root barrier is a durable plastic that prevents root encroachment and protects the membrane. The drain mat, a geotextile fabric installed over the root barrier, ensures that excess rainwater flows to roof drains or gutters. The retention fleece, a non-woven fabric, goes on top of the drain mat. It serves as a filtration barrier against media erosion and facilitates distribution and temporary storage of rainwater. In most installations, additional growing medium, a lightweight mix of porous mineral aggregate and composted organic material, is spread out over the retention fleece before the mats are rolled out to complete the installation.
“All the materials for installations in the U.S. are 100 percent American made,” said Ancaya. “For projects in the Southeast U.S., Xero Flor grows its plants in Durham County, North Carolina. So when we roll out the mats, the full-grown plants are already adapted to the regional climate.”
The green roof visually extends the landscape toward the lake; July, 2013.
Courtesy of Living Roofs, Inc.
Project Challenges, Solutions
Because of the slope of the roof, a supplemental stabilization grid was integrated within the green roof assembly. It was installed over the water retention fleece before the growing medium was added. The grid utilizes TerraCell 140 from Hanes Geo Components (Winston-Salem, N.C.). TerraCell is a cellular confinement system made with high-density polyethylene strips bonded together to form a honeycomb configuration. The grid is anchored on the aluminum drain-through edging at the perimeter of the roof.
Installation of the slope stabilization grid. Photos Courtesy of Living Roofs, Inc.
The Living Roof installers filled the grid with two inches of growing medium before rolling out the green roof mats. The cells of the grid hold the growing medium on the slope.
Choosing green roof plants proved to be another project challenge. “Initially, I wanted the roof to have a uniform, manicured appearance,” the homeowner recalled. “I did not want a wild meadow of plants with all sorts of different shapes, sizes, heights and colors.”
The growing medium is filling in the grid. April, 2012.
Installing the Xero Flor pre-vegetated mats.
The private home after installation. Photos Courtesy of Living Roofs, Inc.
“When designing a green roof, as we inspect the roof we take note of features (such as windows that reflect the sun and areas with shade) that may create micro-climates within the vegetative field,” explained Ancaya. “It is difficult to predict exactly how plants will respond and which will thrive in different sections of a roof. That is why it is so important to choose appropriate plants and create a diverse plant palette. For immediate success and long-term performance, it is better to have diversity so the plants can adjust themselves during the green roof establishment phase.”
“Variety promotes a dynamic plant community that sustainably adapts to the conditions and micro-climates on each rooftop,” said Rugh. “We typically include 8-15 different species of Sedum and other succulents in our plant mixes. For example, our Southeast U.S. Plant Mix features a dozen species suitable for the regional climate.”
Nice red winter color; February, 2013. Courtesy of Living Roofs, Inc.
After discussion with the architect and conversations to inform the homeowner of the importance of diversity, a six-species plant palette was selected for the project. The six species provide enough diversity, and the Sedum spurium and Sedum album give the roof its reddish colors in the fall.
The green roof was completed in April 2012. After three growing seasons, has it lived up to expectations?
Lake Toxaway fall colors from the master bedroom. Photo Courtesy of Platt Architecture.
“The green roof is consistent with the style of the home, complements the natural materials we used in constructing the exterior, softens the appearance of the roof, and blends the roof into the landscape,” said Platt. “It has become a local landmark.”
“I was concerned about driving up and seeing an unkempt appearance or bare spots. The green roof looks great, especially in the fall with the autumn leaves on the trees around the house and the lake in the background,” said the homeowner. “We cannot imagine our wonderful home without the green roof. It just wouldn’t be the same.”
October, 2012. Photo Courtesy of Living Roofs, Inc.
Green Roof Maintenance
Living Roofs, Inc. made ten maintenance visits during the first year. The roof now gets six visits annually. The roof is irrigated with lake water from early May to early October. As part of routine maintenance, Living Roofs tests the automated irrigation system for correct coverage, pressure and timing, and they make adjustments for seasonal temperatures and rainfall. In October, they shut off the system and winterize it. The maintenance plan also includes annual soil testing and fertilization.
Courtesy of Living Roofs, Inc.
“The upper slope along the ridgeline dries out more quickly than lower portions of the vegetative field,” said Emilio Ancaya, GRP, of Living Roofs, Inc. “We anticipated that, watched it carefully, and in the first year adjusted the irrigation pattern to more frequent, short bursts of water.”
Courtesy of Living Roofs, Inc.
Reflection from the windows stresses adjacent plants in one section. Living Roofs added a few micro-sprayers as well as supplemental plant cuttings. This has kept that part of the roof flourishing.
Irrigation detail. Photo Courtesy of Living Roofs, Inc.
And, what about weeds? “The Xero Flor system is pre-vegetated and has extensive coverage from day one. That makes it tough for weeds to get established,” said Ancaya. “In late summer during peak growing season, we collect less than a quarter of a five-gallon bucket of weeds. During our other maintenance visits, we see even less than that.”
With the green roof, the garage is part of the landscape. Courtesy of Living Roofs, Inc.
Stormwater Reduction, Improved Water Quality
Reducing run-off was not a primary goal of the project. It is a valuable, added benefit.
Lake Toxaway averages more than 90 inches of rainfall annually. The summer of 2013 was especially rainy in western North Carolina, with many areas getting almost 30 inches above normal rainfall. Given the area’s typical pattern, and the retention capacity of the installed Xero Flor assemblies, the 3,959-square-foot green roof annually prevents about 99,850 gallons of stormwater from running off into Lake Toxaway. The green roof enhances the lake’s water quality.
Pristine Lake Toxaway.
“The green roof filters rainwater and buffers acid rain, which is a problem in this part of the country,” said Clayton Rugh, Ph.D., of Xero Flor America. “Rainwater not retained and evaporated up on the roof is neutralized and less acidic before it reaches the adjacent shoreline and the lake.”
Publisher's Note: For complete participants of record including designers and manufacturers, plus additional component information, see the Private Lake Toxaway, NC Residence Green Roof project profile in The Greenroof & Greenwall Projects Database.
David Aquilina, Strategic Storyteller
David Aquilina, Strategic Storyteller (www.linkedin.com/in/davidaquilina), is a corporate communications consultant and freelance writer. David makes his home up on the edge of the northern prairie in Minneapolis, Minnesota.
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