Many companies today claim they are proponents of a sustainable future, but few are involved in forging the path that will lead there. Carolina Stalite Co. is leading the sustainable revolution through its horticulture division, creating lightweight aggregate and soil mixes for both small- and large-scale landscape projects such as green roofs.  

The fastest-growing markets for Stalite’s horticulture division are green roofs and bio-retention media for rain gardens. “Right now, green roofs are the biggest portion of our horticulture market,” Horticulture Product Manager Chuck Friedrich says.

Innovation has played a major part in Stalite’s success. In 1991, the now 57-year-old company started a new division that emphasized the use of lightweight aggregates in horticulture applications. To determine whether or not the product was feasible as a soil amendment and propagation medium, Stalite sought out Friedrich, a local landscape architect at the time with connections to the horticulture community.     

After testing the material, Friedrich found some surprising results: The lightweight aggregate was ideal for use as a landscape media to condition the compacted North Carolina red clay. Because of its high porosity and durability, the results are permanent. The physical characteristics of the product ensured its success as a soil amendment. Those same benefits provided a perfect fit as green roof media.

In 1992, Friedrich was hired as the horticulture product manager for the purpose of developing the product for the market.

After four years of testing and fine tuning, the Salisbury, N.C.-based company introduced PermaTill, a lightweight slate aggregate that is highly porous and environmentally inert with a pH of 8.5, making it ideal for landscaping and lightweight fill applications. Because PermaTill has low density, low specific gravity and low absorption, it stays in place and releases moisture and nutrients to plant roots as needed.

PermaTill is used in several technical applications including green roof planting media, structural soil for urban trees, turf and fire lanes, stormwater management, soil conditioning and geotechnical fill. Many green roofs collect runoff, control pollution and reduce utility costs by absorbing heat or insulating the building from the elements.

Successful Projects
In the past decade, the company has contributed to more than 140 green roof projects in 26 states, including its first in 1995 at the U.S. Naval Academy in Annapolis, Md., and the International Plaza in Atlanta.

Following these, dozens more high-profile projects have been completed such as Ford Motor Co.’s River Rouge Assembly Plant in Dearborn, Mich.; Discovery Channel headquarters in Silver Spring, Md.; and the Montgomery Park Business Center in Baltimore.

Several other green roofs have been installed at universities and public facilities, it says. Green roofs do have limitations, Friedrich says. Weight, site access, cost and difficulty in finding sturdy growing material must all be considered.

Hot Process
Stalite operates two production plants in Gold Hill and in Aquadale, N.C. The Gold Hill facility has seven kilns and rests on 500 acres, 40 of which are used to produce lightweight aggregate. Put on line in the early 1970s, the plant gets material from a 200-acre quarry behind the facility, which is operated by Vulcan Materials. In 2004, Stalite purchased the plant and onsite quarry in Aquadale as demand for its product grew. Situated on 670 acres, 20 acres are used for production space, and it operates two kilns.  

Using the company’s rotary kiln process, raw slate from storage silos is fed into pre-heated rotary kilns where it’s heated to more than 2,200 F. When the slate reaches such high temperatures, the expanded gases form small cells that remain after the cooling process, thus giving the material its low unit weight and porosity.

After the product is cooled, crushed and screened, it is blended using an automated system. The expanded slate undergoes a rigorous, hourly testing process to ensure the proper gradation, moisture content, specific gravity and unit weight.

The main end-use of the product is for the production of lightweight structural concrete and concrete block. The company sells product for the construction of large concrete structures such as bridges, buildings and even off-shore oil rigs. For horticulture use, product is used by landscape architects, civil engineers, arborists and environmental engineers on a national and international level.

Stalite distributes the lightweight aggregate and blended product directly to end-users within a 400-mile radius of its production facility. In other cases, lightweight aggregate is distributed to companies who customize their own blends for specific applications.

Material is shipped worldwide via truck, rail or barge, depending on its destination. Strict order-processing and shipping standards are upheld at all times to ensure the client receives the specified product. Trucks are routinely inspected and washed before loading and its scales are checked for accuracy.  

Stalite sells both a standard blend and blends customized to a client’s specifications. “We respect other recipes that people give us and they are confidential,” Friedrich says.

On the Cutting-Edge
Environmental stewardship permeates well beyond how the materials perform in the field. The company is working to incorporate sustainable practices into its manufacturing operations using recycled product. “We’re developing a 50 percent recycled green roof product to be ready next year that will allow us to work with byproducts of the quarry and in the plant,” Friedrich says. “It’s really going to be exciting, because that’s what the green industry will be demanding in the future.”

Friedrich says the company will increase efforts to improve production methods, applications and technical knowledge. The company is also working with the Expanded Shale, Clay and Slate Institute and North Carolina State University to study how aggregate can be applied to water filtration and purification systems at wastewater treatment plants.

Eco-Friendly Project
In 2005, Stalite supplied materials to its largest green roof project to date for the city of Nashville’s Metro Courthouse Public Square. Working in conjunction with local landscape architect Hawkins Partners, Stalite provided the lightweight aggregate fill, structural soil and growing media for the rooftop public plaza as part of a $1 million renovation of the city’s Metro Courthouse complex.

The downtown site consists of approximately 7.5 acres, 2.25 acres of which is a state-of-the-art, intensive green roof over a five-level subterranean parking garage. According to Laura Schroeder, a landscape architect with Hawkins, the design team’s concept was to establish an open and accessible space for the public while it remained sensitive to the environment. An uneven work surface atop the structure required Hawkins to add structural soil to lessen the slope.

“The biggest benefit we found when doing the project is that we had the ability to put down structural soil on top of the pavement, and because of the nature of the rock shape, you still have room for the roots to grow,” Schroeder says.

From November 2005 to June 2006, Stalite provided for the project 4,268 tons of fill under the growing media, 5,300 tons of growing media and 1,200 tons of structural soil for the street trees planted on site. “Our experience with [Stalite] has been nothing but good,” Schroeder says. “[Stalite] fills a niche and they have been the forerunner.”

The roof cost $30 per square foot to build and incorporates 43 different species of landscape materials, about 80 percent of which are native to middle Tennessee. Rainwater that falls on the rooftop and water from a garage sump is captured in a 57,000-gallon below-grade tank. This water is filtered and re-circulated for the landscape irrigation system. “The public awareness of green roofs has grown in leaps and bounds,” Schroeder says.

A ‘Growing’ Trend

Carolina Stalite Co. has found its niche in the sustainable revolution, creating horticulture aggregates for commercial landscape applications.

Perhaps that’s because, according to Peck, “nothing can deliver the same range of benefits that a well-designed, installed and maintained” green roof can. 

Although the benefits of green roofs are plentiful – reduction of storm water runoff, heat and sound insulation, energy savings, improved air quality – the concept is still in its infancy in North America. “If you look at the green roof industry in Germany and see approximately 1.9 billion square feet installed since the early ‘80s, what we have accomplished in North America is the tip of the iceberg at just over 3 million square feet,” Peck says.

The nonprofit Green Roofs for Healthy Cities works to promote green roof infrastructure, increase awareness of the economic, social and environmental benefits of green roofs and advance related products and technologies.

Although capital costs are indeed a factor, Peck notes costs depend on how the design is integrated into the building and what function the roof is supposed to serve. Implementation in the private sector is partly dampened by the nature of development. Since many developers build to sell, few are interested in accruing additional costs for a feature they won’t economically benefit from in the long-term.

“Generally speaking, we are seeing more green roofs on public buildings, in part because our civic leaders are leading by example and also in part because many of the benefits are long-term,” Peck says.

Public policies and incentive programs could be the answer to promoting more widespread adoption of green roofs in the private sector. Chicago has policies in place to support green roofing, which helps it lead the way in green roof implementation among U.S. cities. The Green Roofs for Healthy Cities Local Market Development Program attempts to form public-private partnerships to spur green roof development.   

Incentives such as a density bonus program, fast-track permitting, green space allocations, low-interest loans and reductions in stormwater management fees are all ways that municipalities can take the lead in green roof policy development.

“Green roofs enable policy makers to leverage private roof space and private roofing investments into a technology that delivers multiple infrastructure benefits,” Peck explains.

The association’s second annual survey of its corporate members indicates that green roof installation increased more than 25 percent from 2005 to 2006, accounting for more than 3 million square feet of installed green roofs.

For more information, visit www.greenroofs.org.