Tar Heel State Trailblazers

Fall 2012

North Carolina stands at the vanguard of permeable pavement possibilities.

By Meredith Landry

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Tar Heel State Trailblazers

The parking lot for the North Carolina chapter of the American Institute of Architects (AIA) building in downtown Raleigh had to be more than a place to park. The organization’s impeccable 12,000 sf (1,200 m2) headquarters was completed late last year and earned Platinum-level LEED credits. The post-modern building was designed by renowned architect Frank Harmon, FAIA , whose rm won a professional competition for the project in 2008 because it promoted “healthy urbanism.” This is evident inside the building and in the exterior landscaping and parking lot, which together provide exemplary integration of modern design with sustainable practices.

On a site smaller than an acre (0.4 ha), the remaining area around the building needed to accommodate landscaping and a parking lot for 36 cars. This immediately presented a challenge, says Harmon, who turned it into an asset. “We decided to turn this problem into a virtue by making a parking area that could be used for many purposes in addition to parking,” he says. “We called this area the Parking Garden, so it could be used for sculpture exhibits, outdoor movies, street parties, a farmers market and other events connected to the building’s large multi-purpose room.”

This meant the lot not only had to be attractive, it also had to be useable immediately after inclement weather. So, naturally, Harmon selected permeable pavement. And when he envisioned a herringbone pattern using interlocking concrete pavers, the ICPI member contractor delivered.

Over four weeks in December 2011, the contractor installed the 8,200 sf (760 m2) parking lot using permeable interlocking concrete pavers that incorporated some of the building’s blue tones. His crew installed most of the pavers with mechanical equipment to reduce construction time and costs. According to the contractor, mechanical installation of the concrete pavers saved at least a week’s worth of labor costs.

Mechanical installation requires one person operating the machine and one person helping to set and align the pavers on the permeable bedding material. Once the paver joints are filled with permeable aggregates and compacted, the owner has immediate use of the surface. In contrast, pervious concrete requires about a week to cure and porous asphalt at least 24 hours before receiving vehicular traffic.

Not Just A Pavement

Although the mechanical installation saved significant time and money, some of the detail work had to be done by hand to achieve Harmon’s standards for appearance.

To achieve Harmon’s desire for a continuous herringbone pattern, the installation crew stitched the mechanically placed paving layers together. Each square yard (m2) layer has a few half pavers on the layer sides. These half pavers are removed during layer placement, replaced by whole units to continue the herringbone pattern from one layer to its neighbors. This creates a consistent pattern across the surface and suggests a customized appearance.

Adding customization, the contractor gave the lot permanent parking stall stripes by creating them with a different color paver. As a result, the building owner eliminated time and money spent maintaining painted stripes on the lot’s surface. Other permeable surfaces don’t provide this option.

Because of its adaptability, sustainability and increased affordability, permeable pavement has seen a rise in demand every year for the last five years in the region. Frank Harmon hopes that the AIA project will inspire more developers to follow suit and increase that demand even more. “We like to think that our building and landscape raises the standard of sustainable design,” Harmon says. “Being in the capital city and located a few hundred feet from the state legislature, it will, we hope, become a role model.”

Leading By Example

Permeable interlocking concrete pavers have already found their way into other parts of Raleigh, a city where excessive stormwater runoff is one of the most pressing environmental challenges, according to Harmon. Completed in the fall of 2011, the North Carolina Department of Environment and Natural Resources (NCDENR) in downtown Raleigh included a permeable interlocking concrete pavement sidewalk as part of its Green Square Complex, a two-block, multi-use, sustainable urban development that houses the NCDENR headquarters, the North Carolina Museum of Natural Sciences’ Nature Research Center and underground parking for 426 cars.

“This is one of the first installations of a permeable paver system within a public streetscape in North Carolina,” says Jonathan Parsons, a project landscape architect for O’Brien/Atkins, the Durham-based firm responsible for the design of the complex’s sustainable systems. The NCDENR permeable paver project consists of 7,100 sf (660 m2) of sidewalk placed in phases over three months.

“This state agency project clearly sets the example for the rest of the state. They’re incorporating green building principles in a downtown area with far too many hard surfaces,” Parsons says. “Hopefully other urban settings across the state will realize the benefits from these principles.”

A Balanced Environment

Raleigh is typical of most urban areas with expansive suburban development surrounding an urban core. Over the years, development impacted multiple streams within the drainage basin, according to Parsons. “Impacts include sudden changes in flow volume and intensity during rainstorms, plus temperature spikes caused by runoff flowing into the streams from paved areas,” he says.

Raleigh in particular has been slow to accept permeable pavers since the clay soils in this part of the state infiltrate slowly, Parsons says. However, the state as a whole has made significant progress in expanding acceptance of permeable pavement as part of a site’s stormwater management plan.

Between 1999 and 2005, North Carolina State University conducted several studies on permeable pavement for infiltrating stormwater runoff, all of which showed positive performance for runoff reduction. Two of these studies were co-funded by the Interlocking Concrete Pavement Institute. As a result, North Carolina State University faculty convinced NCDENR regulators to accept permeable pavement as a stormwater best management practice in 2006. NCDENR recently released revised design guidelines on permeable pavements. The 40-page document provides pollutant credits and site coverage credits to builders and homeowners for using permeable pavements across the entire state. The 2006 edition only provided such credits to the eastern counties with sandy soils.

Permeable pavement enables larger buildings and more efficient site use because the pavement manages the water on the site. The municipal storm drainage systems see less runoff and that reduces public expenses. For Frank Harmon’s project, the permeable interlocking concrete pavement collects all roof runoff and 90 percent of rainwater stays on the site. “If you stand in a mature mountainside forest as it rains, you’ll notice that 90 percent stays in the forest,” he says. “That’s how nature intends it to be in a balanced environment.”

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