But while the primary use of pervious remains in the construction of commercial parking lots, industry observers say that some parts of the country are seeing an increase in the use of pervious for residential applications—especially driveways, but also pool decks and patios, as well as residential streets and walkways.
Pervious concrete is a mixture of coarse aggregate, portland cement, water and little to no sand. A typical pervious concrete pavement allows three-to-eight gallons of water per minute to pass through each square foot. The material is bonded with a paste consisting of carefully controlled amounts of water and cement material, resulting in very high permeability that drains quickly and, because of the low paste content, very light weight.
Atlanta-based PCI Systems, which transitioned from a traditional concrete contractor to pervious specialty firm five years ago, now does about a quarter of its jobs in the residential market.
But PCI’s president, L. Dale Fisher—who travels the country espousing the virtues of pervious—says the volume of those residential jobs is insignificant compared to the parking lot work that still makes up the bulk of PCI’s business.
“If you look at volume, it’s nothing,” Fisher says. “One driveway compared to three parking lots. You can imagine the quantity. It’s a very niche market. In metro Atlanta, we’ve had three communities here where they have maximum density coverage, so pervious concrete is a good fit for driveways in those areas, but it would take 30 to 40 driveways to equal one parking lot.”
But Fisher sees the niche market of pervious in residential as having growth potential, which is why PCI takes the jobs and does not charge a premium for their small size, as he suspects many other contractors would.
As more residential developments end up with high density, he says, developers will have a more difficult time adding amenities like garages without being considered out of compliance with water runoff regulations. A pervious driveway, which all but eliminates water running off into storm sewers and the need for retention ponds, can often be the difference that will result in approval for the desired garage.
In the Atlanta area, Fisher says many homes are being developed on quarter-acre lots, which creates tremendous pressure with respect to stormwater runoff.
“On the residential side, it’s a pavement that acts as a low-impact development as far as stormwater is concerned,” Fisher says.
It is also becoming more common for residential streets in new developments to be built with pervious, a practice that is growing fastest in northern California, where the Tahoe Regional Planning Authority—the area’s leading regional development authority—is mandating more aggressive approaches to stormwater runoff in residential areas.
“They’re the 800-pound gorilla of regulatory agencies, and they control what happens buildingwise,” says Andy Youngs, technical consultant for the Southwest Pacific Concrete Association. “They approved pervious about three years ago as a filtration management process.”
The use of pervious driveways, Youngs says, allows many residential developers to avoid having to install sodded drains at the end of every driveway.
“Instead of doing those sodded drains, they’re doing either entire driveways of pervious concrete or infiltration trenches with pervious concrete,” Youngs says. “Over the course of the past three years, there’s one company that has done about 1,000 pervious concrete jobs—most of them three-to-six-foot-wide strips at the end of the driveway.”
Young says he also saw a subdivision in Washington state in which all hardscaping was done in pervious—including all roads and sidewalks. The result was the elimination of all retention areas.
“They made an extra $1 million over and above their costs,” Youngs says.
Despite these examples, pervious in residential applications remains a blip on the national radar screen with serious potential, according to Jim Niehoff, residential promotion manager for the Portland Concrete Association.
“If you’re in an area that tends to flood in a heavy rain, where the sewer system just can’t handle the rainwater in that area, it’s just a matter of time (before pervious grows as a residential application),” Niehoff says.
At present, however, Niehoff does not believe the market is prepared for a major increase in residential pervious work.
“It’s going to be a matter of having enough contractors who are certified to handle pervious in residential applications,” Niehoff says. “That might take awhile, but it’s coming.”
In an attempt to address the certification issue, the National Ready Mix Concrete Association has developed a certification program for contractors who want to work in pervious. The program is designed to be administered locally, and offers to levels of certification—Pervious Concrete Technician and Pervious Concrete Craftsman. The former requires the passing of a written exam. The latter adds a degree of actual experience working with pervious in the field.
Fisher says certain kinds of concrete contractors are more natural fits than others to move into pervious.
“I wouldn’t say so much the structural or traditional road builder,” Fisher says. “But a flatwork contractor, definitely. A good fit is a flatwork contractor who does parking lots and things like that, and has a lot of attention to detail. They are a good fit for pervious concrete.”
Rocky Geans, owner of Mishawaka, Indiana-based L.L. Geans Construction, recently became certified to do pervious work. But Geans expresses a concern about the long-term implications of the water seeping through pervious over many years.
“My concern is the silty material that the stormwater washes through there,” Geans says. “How do you clean it out? It’s been says that you vacuum it out, but you’re only going to vacuum out so much. What is the product like after 10 years?”
Geans says his company recently installed a pervious parking lot for a local ready-mix company, and while the pervious is performing as intended with respect to water running through it, he is already noticing side-effects that make him wonder about the long-term viability of the substance.
“All the water washes off, but the leading edge of the pervious has already started to silt up,” Geans says. “That’s something I want to investigate more. What happens with the fine silty material if you go down through all the pervious and get down to the aggregate? It’s gong to back up and get to the point where it’s filled up. It will most likely happen on the leading edge.” In commercial parking lot applications, the popularity of pervious is growing as part of the emerging movement toward green building.
PCI Systems was recognized in 2005 for its contributions to an “eco-office” development in the Atlanta area, and is working to refine its mixing techniques to make pervious even more effective in all applications.
“For three years, we’ve worked with some companies developing better mixers,” Fisher says. “We’re just fine-tuning our mixtures to have an easier placement and more consistent placement. We’ve also worked with some equipment manufacturers developing some good applications for pervious.”
PCI decided to focus on pervious when it saw the market need developing in the late 1990s.
“Back in the late ’80s, we would do pervious in Florida from time to time, but it wasn’t huge,” Fisher says. “The market wasn’t demanding it for large parking lots. So we did pervious along with other things. In the late ’90s, when the market changed and the development market really had a need for pervious, that’s when we realized we need to focus on pervious concrete.”
By taking on so many small driveway projects with very little profit involved, Fisher is betting that the residential market is going in the same direction.