Permeable pavers are one of the most widely used LID-related products on the market.
Written by Janet Aird
“The use of permeable pavers has gone rampant,” says David Hein, an engineer with Applied Research Associates in Toronto. “It’s driven by the stormwater people. There’s been a major effort to deal with stormwater at the source.”
While the goal of poured concrete and asphalt is to guide water away from their surfaces, the goal of the permeable paver system is to allow it to infiltrate into the ground below. And although they’re used most frequently for parking lots and driveways, they’re also suitable for a wide variety of surfaces, from sidewalks and plazas to roadways where the speed limit is 40 mph and under.
“They’re used in intermodal terminals where 25,000 vehicles drive over them,” says Hein, who has recently conducted webinars on Design, Construction and Maintenance of Permeable Pavement through Forester Media’s new education program. “We even ran an Abrams tank over some. They worked extremely well.”
The cost of laying permeable pavers is somewhere between the cost of laying asphalt and concrete, but because stormwater infiltrates between them and is detained between the stones underneath, pavers are ultimately less expensive than asphalt because there’s less need for storm drains, pipes, detention ponds, or other stormwater infrastructure. In addition, they don’t have the attendant problems of flooding, groundwater depletion, and downstream water erosion and pollution.
|Good design and installation are essential to stormwater infiltration and retention.
|Photo: APPLIED RESEARCH ASSOCIATES
The use of permeable paving stones goes back to when the Romans built the Appian Way, 2,000 years ago. Some of the roads are still in use today.
Pervious pavers are durable, because the concrete is compressed during the manufacturing process. “They’re two times stronger than concrete, and they already have cracks,” says Hein.
If one or more pavers are damaged for some reason, it’s easy to replace them. If a pipe breaks underneath them, they can be removed above the break, the pipe can be repaired, and the same pavers can be replaced without anyone being the wiser.
With concrete, says Michael Gerber, owner of J.M. Gerber Construction in Simi Valley, CA, “if I make a saw cut, you’ll see the patch, and the labor will take a lot longer.” Gerber laid the pavers for the Sierra Pacific Constructors parking lot, described in this article.
Good design and installation are essential. The Interlocking Concrete Pavement Institute is one source of information, and its software program, Permeable Design Pro Software, integrates both hydrological and structural solutions.
“If it’s not done right, they’re more prone to failure,” Hein says. “It isn’t hard to do correctly.”
Kenan Hall Plaza
For years, the entrance to Kenan Hall at Flagler College in St. Augustine, FL, needed a creative design to reveal its potential.
“It was a low area in front of the building,” says Sharon Fowler, ASLA, principal of the landscape architecture firm Hauber Fowler & Associates LLC in Longwood, FL. “After a strong rain, water would pool there and students would have to walk through it.”
Fowler, with the college’s campus planner, Larry Weeks, designed a plaza for the front of the building, turning the 5,000-square-foot space into a showcase that not only handles the stormwater but also has become a very functional space for the students, faculty, and visitors to the college. The entire plaza is constructed of StormPave permeable pavers from Pine Hall Brick in Winston-Salem, NC, to allow maximum infiltration as well as complement the architecture of the building.
The project won the Brick Industry Association’s Brick in Architecture Silver Award in the Paving and Landscape Architecture category in 2011.
“St. Augustine is in a low-lying area with stormwater challenges,” Fowler says. The city, only 4 miles from the Atlantic Ocean, requires that new construction—in this case, the plaza—to keep its storm drainage onsite.
Most of the college’s classes are taught in Kenan Hall. It was originally built as the quarters for the seasonal employees who worked at the adjacent Ponce de Leon Hotel, a winter resort for wealthy northerners. Both buildings were constructed in 1888 by Henry Flagler, a partner of John D. Rockefeller in Standard Oil. The buildings were donated to the college when it was founded in 1968.
Today, they are in the city’s Historic Preservation District. Kenan Hall and the former hotel, now Ponce de Leon Hall, were the first structures in the United States constructed principally of poured coquina shell concrete. This material, a sedimentary rock composed of fragments of seashells and corals, was used as a building stone in Florida for more than 400 years. It is a warm gray color.
The challenge for Fowler was to find a permeable paving system that would fulfill the city’s requirements for onsite drainage retention as well as meet the design standards of its Historic Architectural Review Board. The board requires designs in the district to use materials that reflect those that were used at the time. Fowler also wanted the plaza to complement and enhance the building.
|Photo: HAUBER FOWLER & ASSOCIATES
Old utilities and drainage pipes can make excavation a challenge.
|Employees sweep crushed limestone between the pavers to lock them in place.
Fowler found Accent Gray, a paver from Pine Hall Brick that was almost a perfect match, through the distributor, Oldcastle Coastal of Jacksonville. She used Pine Hall Brick’s Autumn paver to complement the building’s deep red and terra cotta accents.
“These pavers are made of clay,” she says. “Their texture and color are integral, and they match the building almost perfectly. I think they will stand the test of time.”
Decorative elements in the design include large date palms and cast stone planters that replicate the original coquina planters. Even the aluminum and plastic recycle bins blend in.
“Almost everything was selected or custom made to go with the architecture,” she says. “It was wonderful to work with the college. They wanted to do everything right.”
The project brought a number of people with a wide variety of knowledge and skills together, beginning with the excavation.
“When you excavate next to an historic building, there are a lot of utilities and old drainage pipes that might collapse,” she says. The mason contractor, Paverscape Inc. in St. Cloud, often found pipes that had to be moved, and by chance, one of the college staff who had been at the property before it became a college was able to identify them.
Paverscape excavated 18 inches down and placed a filter fabric on the soil. Crews laid a 12-inch layer of large, clean stone, then a layer of medium stone, and finally a layer of fine gravel on top, leveling, rolling, and compacting each layer. They did an overall leveling before they started applying the pavers.
“You put the larger stones on the bottom so the water rushes down and then out to the surrounding area,” Fowler says. “Any impurities in the water are taken care of as it percolates through.”
She designed the plaza to slope toward the lawn areas so excess stormwater runoff would outfall there, but so far the pavers have handled it all.
“It was probably challenging for Paverscape,” she says. “I designed an intricate paving pattern with a flush granite logo in the center of the plaza, and I didn’t want small pieces. The pavers should be at least half a paver in size so they can’t come out easily.”
The pavers have less than half an inch between them, which meets Americans With Disabilities Act (ADA) regulations. Paverscape swept No. 89 crushed limestone between them to lock them in place. The only maintenance is to vacuum once a year.
Fowler considered function as well as design and drainage. “I spent a lot of time thinking about how the space would be used,” she says.
The plaza has poured-in-place coquina concrete columns that she designed to be wired for lighting and electricity, so the students can use their laptops and other devices. Chairs and tables can be moved around to accommodate different groups, and low retaining walls can be used for seating.
The plaza was built during the summer of 2010 and was completed in August, before the students returned from summer vacation. Fowler stayed onsite at least three days a week to make field adjustments, and the campus had to be closed while the general contractor, A.D. Davis, relocated some walkways to lead visitors to the plaza.
“I couldn’t be happier with this project,” she says. “When I’m on campus for meetings, I love to see people congregating there. When the students tell me it’s great, I ask them: ‘Do you know there’s a drainage system under here?’”
PCC Rock Creek Recreation Facility
The Tualatin Hills Park and Recreation District (THPRD), just west of Portland, OR, needed a new facility to serve its current and future residents. The area is mostly suburban, but there’s a significant amount of rural land, and officials are expecting more development in the next 10 to 20 years. They had the funds to build the facility, but not the land. The adjacent Portland Community College needed sports facilities and recreational areas to enhance the curriculum at its Rock Creek campus. The college had the land, but not the funds.
The two combined resources, and today they share the 32-acre PCC Rock Creek Recreation Facility, which includes sports fields, tennis courts, and a trail for walking and jogging. The college uses the facility during the day on weekdays, and the recreation department uses it in the evenings and on weekends.
One of the goals of the project was to use as many sustainable techniques as possible. This included installing permeable pavers in all 286 parking spaces in the facility’s parking lot. The design called for the SF-Rima permeable paving stone system, which is licensed to SF Concrete Technology Inc. in Mississauga, ON, by the developer of the system, SF-Kooperation GmbH in Germany.
“They were brought to us by the facility’s designer, Mark Hadley,” says Gery Keck, THPRD’s senior park planner, who was involved in the project from inception to completion. “He saw them when he visited Europe. They seemed to meet a lot of our goals.”
Hadley, a landscape architect with W&H Pacific Inc. in Portland, was the design team project manager on the job. The pavers cover a total of 47,000 square feet, slightly more than an acre. The rest of the parking lot is asphalt.
The project won a design award from the Oregon Recreation and Parks Association in 2007, in large part because of the sustainable techniques that were used. These include synthetic turf, state-of-the-art irrigation and lighting systems, recycled plastic outdoor furniture, and bioswales in addition to the pavers. “It was an honor to get that award,” says Keck.
One challenge in making the facility a reality was getting THPRD, the college, a 12-member task force, multiple districts and jurisdictions, and other concerned parties to agree to a master plan and design, Keck says. Discussions about building a facility began in early 2000. Construction began in 2006 and was completed in 2007.
“You need to keep an open dialog,” he says. “Most user groups got a piece of what they wanted.”
The area is hilly, with creeks and streams running through it. Because the facility is on a downhill slope, the biggest challenge in the construction of the parking lot was that of creating a level surface. Kerr Construction in Woodburn, OR, poured the asphalt for the driveway and the concrete for the curbs, which have cuts to allow runoff to flow from the parking spaces into bioswales in the parking lot. For the parking spaces themselves, Kerr excavated between 15 inches and 2 feet, depending on the project’s specifications, and then graded and compacted the area.
Runoff from the heaviest rain events is treated by a system of bioswales, all of which are planted with native plants.
Crews placed a filter fabric on the excavated soil; poured layers of half-inch clean, dust-free stones; and compacted each layer until the stones were up to grade. To level out the top layer of stones and provide a smooth bed for the pavers, they laid a screed layer of clean quarter-inch stone on top.
The 10- by 10-inch concrete pavers, manufactured by Willamette Graystone in Oregon, will last longer than asphalt, Keck says. The open space between them is approximately 9 to 10%, the optimum amount to infiltrate runoff, according to SF Concrete Technology. The pavers must be very consistent in size when they’re mechanically laid down, and if curbs or other design elements are even a little bit off, they have to be removed and rebuilt before the pavers can be installed.
Modular Paving Systems Inc. of Tigard, OR, laid down the pavers with a Probst PaverMAX VM 204 paver-laying machine from Germany. The machine set the pavers into the parking spaces flush with the curb on three sides—approximately 5,000 square feet of pavers a day.
“The pavers come on pallets,” Keck says. “The machine picks up the top layer, puts it down, and sweeps screed into the joints.” This screed is also a quarter-inch in size.
Maintenance is simple. Workers blow off grass clippings, pick the few weeds that come up, and vacuum any silt that plugs the spaces between the pavers.
Approximately 90% of the rain events in the Portland area are low volume and long lasting and are easily handled by the pavers. Excess runoff from the remaining 10% flows to a system of bioswales, all of which are planted with native plants.
“If we get a downpour, it’s not going to go between the pavers,” Keck says. “It’s going to run on top to the bioswales in the center of the parking lot.” Runoff from the heaviest rain flows into catch basins and from there to additional bioswales. All the water from the site eventually hits one of two large water-quality swales, where it is treated before it reaches a creek on the western side of the facility.
As part of the project, THPRD restored a 50-foot buffer along the creek. “It’s a requirement if there’s any type of wetland or creek,” he says. “For the length of the project we took out invasives and planted over 1,500 native plants, shrubs, and trees. We also maintain it.”
The sports fields are multiuse. “When we talk multiuse, we really mean it,” Keck says. “It’s more sustainable for us.”
On 11½ acres of the facility is a grass area with soil engineered to hold moisture and therefore require less irrigation. With a “flipped design,” portable outfield fencing, and removable bases, the area can be used as four fields for Little League, softball, or baseball. When the fencing is removed, it can be used as three soccer, lacrosse, or football fields.
The synthetic turf fields are used for soccer, lacrosse, and football. Below the 2-inch-high turf is a layer of clean gravel, a layer of flat drains every 15 feet, another layer of gravel, and a filter fabric on the soil base.
“If water hits the gravel, it hits the flat drains,” he says, “and our system dumps it into the water-quality swales.”
Large berms on the southern and eastern boundaries of the facility cut down the noise and light as well as provide seating for spectators. They also provide the space for 500 landscape trees, which were selected from the college’s Landscape Technology program plant identification list for its horticultural class.
The facility has a number of other amenities, including picnic areas and a play area for children. It was funded by system development charges that THPRD collects from developers to help offset the costs of growth within its service area.
“It was a great project,” Keck says. “I’m very fortunate to have been part of it.”
Sierra Pacific Constructors
When a high-end commercial general contracting company updates its parking lot, quality is important.
“They wanted to stay as green as they could,” says Michael Gerber, whose construction company laid the Aqua Roc permeable paver system from Belgard Hardscapes in Atlanta, GA, in the parking lot. “Belgard offers a large array of stones, styles, and patterns. Their colors are very consistent through the stone.”
The general contracting company, Sierra Pacific Constructors in Woodland Hills, CA, has managed projects for such companies as Google and Yahoo, the Oprah Winfrey Network, Los Angeles World Airports, and Aston Martin.
In 2011, the company won the Southern California Chapter of the International Interior Design Association’s Calibre Award, which honors the excellence of a project team in bringing a designer’s vision to life. The same year, Sunset magazine chose one of the Belgard’s permeable paver systems for a 2,800-square-foot pedestrian deck as part of the construction of its annual “Idea House.”
The Sierra Pacific building is in a very densely populated commercial and urban area, a block from the busy 101 freeway in Los Angeles. It may not rain often in southern California, but when it does, the daily rainfall can be more than 4 inches. Most of the stormwater on the building’s site comes from onsite.
Stormwater runoff from the parking lot contains the pollutants that are typically found on parking lots, including hydrocarbons, sediment, and heavy metals. All the runoff used to flow into the municipal storm sewer system and from there to nearby beaches, which often were closed because of water pollution.
The entire parking lot is 14,000 square feet. “The portion we did was the actual parking spaces,” Gerber says. “There are 39 of them in the outdoor parking lot. We laid 5,000 square feet of Belgard’s Aqua Roc Pavers.”
All Construction of Simi Valley, CA, demolished the old parking lot, crushed and recycled the concrete, and installed a drainage system that ties into the municipal stormwater system. Crews poured the concrete driveway and curbs to provide solid borders for the pavers.
“All the concrete work had to be done before the paving stones because the exterior borders of the pavers have to be set up against concrete borders or wet-set in concrete,” Gerber explains. “That prevents any lateral movement of the stones.”
The laying of paving stones accounts for about 75% of Gerber’s work, but this was the company’s first time laying permeable pavers.
“The fact that we hadn’t done it before meant a little bit of a learning curve,” he says. “We had a trial run on one parking stall to see how much the stone would settle when it was compacted. That way we could figure out exactly how high to set our final grade.”
Gerber excavated twice as deep as required for the concrete driveway, approximately 14 inches, to create a basin for the stormwater to sit and slowly seep into the soil. Crews created a layer approximately 6 inches deep of 3- to 4-inch crushed rock, a middle layer approximately 3 inches deep of 1½ - to 2-inch rock, and a top layer approximately 2 inches deep of three-eighths-inch rock. They graded the surface to direct any runoff to storm drains.
“It has to be crushed rock so the jagged edges lock together,” he says. “You want to end up with about 11 inches so the paving stones can take up the last 3 inches or so.”
These stones are 3¼ inches, or 80 millimeters, thick and have spacers on them that set them approximately three-eighths of an inch apart to be ADA compliant. Gerber set them as level as possible on the top layer and then went over them with a compacting plate.
“When you go over the stones with a compacting plate, they’re really smooth,” he says. “Then you put sand between them and vibrate it in. You can drive on them that night.”
Because concrete is porous, the paving stones will absorb oil leaking from cars, he says. “There’s a sealer that can be applied on the stones that keeps oil from sitting on them. One kind doesn’t change the color and the other makes them look wet. If oil sits on anything for a week or two it will permeate, but the sealer will help.”
The entire project took about eight weeks. It was completed the end of December 2011.
“It was a great project,” Gerber says. “We did 5,000 square feet times 14 inches. That will hold a lot of water. We’re so dry all the time in southern California; we need to put as much water into the ground as we can.”
Writer Janet Aird specializes in topics related to agriculture and landscape.