While brainstorming  creative stormwater solutions, ‘paving’ may not rise to the top of the list for most apartment or condominium managers, but maybe it should.  Today’s innovative architects, engineers, designers and green-product manufacturers have been colluding again to great advantage.  Durable, pervious and gorgeous alternatives are available in lieu of out-dated ‘Annie Asphalt’ solutions.  Stormwater management is serious business for most states and particularly urban areas as businesses, citizens and farmers compete for water resources. When stormwater is properly handled, it becomes available for irrigation and replenishes ground water and recharges aquifers. It can also reduce demand on over-extended sewer systems.

Many urban apartment buildings can look stark.  Attempts to soften a cement entryway with a palm or a fern spilling out of a doorway planter can help, but pervious paving has the potential to enhance and update a building’s curb appeal.  It can also replace those walkways improperly graded when installed or prevent erosion from the runoff they create.  Spending money wisely here can solve a storm water problem and attract tenants.

One of my favorites on both appeal and function is a product known as “Drivable Grass”, which can be used for boat launches, private walkways, parking areas, overflow parking, emergency vehicle parking, etc.  It is manufactured, distributed and installed by Soil Retention Systems, Inc.(SRS) of Carlsbad, California.  I corresponded with their sales manager, Jim Engelke, who is a member of ASLA and a LEEP AP as well.  Incidentally, Jim advised me that their products are available nationally to anyone who wants them either through a distributor, or if the territory isn’t covered, SRS will sell direct.

Designed as a flexible matting system, porous grids are planted with a ground cover between the cement ‘pavers’ where a contractor would normally place grout. The system creates evenly-spaced drainage and mimics nature by allowing stormwater to percolate into the ground rather than travel off your property or, worse, join the blackwater in the sewer system.

Sustainability advocates in principle suspect any product description with the words ‘turf grass’ in it.  However, as part of a concrete product designed to recapture ground water, turf grass can be enormously practical and ‘green’. Using a grass variety that is sturdy and drought tolerant and acclimated to your region is important.  Other living ground covers or loose materials like gravel are also options between pavers if stormwater control is your main concern and you don’t want lawn-keeping duties.

These eco-grid paving systems are very high tech and can withstand varying amounts of weight, but it is critical to use the right product designed for your specific traffic load and expected frequency of usage.  Drivable Grass can be used as a pavement system for walkways, driveways and parking areas too.  Each 2-foot-by-2-foot concrete square (consisting of 36 connected mini-pavers) is connected into a mat by a grid system.  Ground cover plantings fill the lattice-style holes and cracks.  According to the manufacturer, as roots penetrate through the mat into the soil, they help anchor the system firmly into place. The mat’s porous nature reduces runoff and allows moisture to filter into the underlying soil.

“Aesthetic solutions to runoff issues are hard to find,” a Building Products’ judge said when Drivable Grass received a Green Products Award in 2008 for innovation.  The judges regarded this paving as “an elegant solution to a common problem.”

Curious about how this product would perform in colder climates, I asked Jim Engelke a few questions.

Editor: Do you recommend any particular turf grass?

Engelke: Because of the varying climate conditions across the country we suggest that turf selections be recommended by a local nursery person familiar with regional requirements. Typically in colder climates it is a Bluegrass mix and in warmer climates it is Bermuda or Zoysia.

Editor: Is the matting affected with freezing ground or lifting?

Engelke: Drivable Grass is made with a low moisture absorbing concrete and will resist cracking during a freeze.  Because the individual concrete pads are connected by a polymer grid that remains flexible even in freezing conditions, Drivable Grass mats will expand and contract with soil movement.

Editor: What is the serviceable life expectancy of the product?

Engelke: Concrete is one of the most durable wearing surfaces for pavement. I should see no reason it would not be usable beyond 50 years.

Editor: Would it work for residential use or for park trails that are now
paved without permeability?

Engelke: Drivable Grass is a perfect choice to replace that old concrete or asphalt residential driveway. It is more attractive and offers opportunity to infiltrate storm water as well as lower the heat island effect on adjoining structures. It would also be good for multi-use park trails where erosion and wear are concerns and can be infilled with native grasses or aggregates instead of turf grass.

Editor: How is it installed?

Engelke: The Drivable Grass system uses a 1-1/2″ ~ 3″ of 80% sand/20% organic mix placed below the mats and infilled above for planting which will infiltrate storm water at a rate of 2″ per hour.

Editor: If this is installed in a colder climate, what are the recommendations for snow plows?

Engelke: In snow conditions it is recommended to leave about an inch on the mats when plowing. This snow will quickly melt due to earth temperature rising through the mat voids. The melt will infiltrate and avoid refreezing on the surface as ice.

Soil Retention has allowed us to use some of their photos above, but their full photo gallery includes pictoral essays of the pavers being employed as a boat ramp installation, overflow parking with artificial grass, a condominium parking solution, residential overflow parking, traffic roundels, residential and nursery walkways and emergency vehicle parking.   How much does it cost?  About $3.00 per square foot before installation.

There are many other pervious paving products which can be part of an effective stormwater management solution.  If you know of a company with a great green product, please let us know with a comment or an email.