Gardening on the Planet, Unusually Clever People

The question of permeable pavers and paving

This is Dave's urban habitat project.

This is Dave’s urban habitat project (detail)

Last week, I posted about a beautiful parking lot that is conserving trees and water. It’s the project of my friend Dave Majewski, who’s been pursuing green infrastructure and remediative landscapes for decades. (This year, Dave received the EPA’s Environmental Quality Award for his urban habitat project on Buffalo’s East Side.) The parking lot is set to be a touring destination for gardening professionals when completed.  In comments, a question came up as to why Dave had used concrete for the lot rather than permeable pavers. I can tell you all from experience that this is would never receive a one-, two-, or even three-sentence answer in the world of Dave, so I worked with him to create a little primer on these materials. (None of this will be news to the pros among our readers, but I know we have plenty of regular gardeners who might not be versed.)

Here's an image of an environmentally friendly parking lot I found on Shutterstock

Here’s an image of an environmentally friendly parking lot I found on Shutterstock

First, he wants to differentiate between permeable paving and pavers.
On permeable paving: What is it?
Either permeable concrete or asphalt, with an ingredient that is left out of the mix to make the finished “slump” product that gets spread and worked throughout the area less impervious. This creates larger air pockets and voids, allowing the runoff to pass through from the surface and down through the hardened permeable/porous paving material, through the sub base and into the water table. Cost is a little more than regular concrete or asphalt paving, or sometimes the same, depending.

Issues:
This process and finished end product will crack—definitely.  (It should be noted that finished concrete—standard type—will also crack. All concrete eventually cracks to some degree; small or large. It is the nature of the material in zone 5.)  This porous/permeable paving surface then needs to be maintained regularly, mostly by vacuuming and regular sweeping/cleaning of the accumulated surface debris (leaf matter grit, soil particles, litter, etc.

On permeable pavers: What are they?
Individual stone/brick units installed under manufacturer-defined specifications that make their installation permeable. Any stone/brick-type material can be permeable. They allow for storm water infiltration off the hard surface. They have their place as a possible storm water runoff solution.

Issues:
Their installation requires extensive excavations to depths of 18” at least, thus increasing the financial and environmental costs. Standard concrete requires half the excavation and removal. Pavers also require increased skilled labor to engineer, prep, adjust, and install, also increasing the cost. (The cost is about 2-3x the cost of standard pavers, if they are installed to the manufacturers specs.)  They do not provide for increased green spaces and native plantings. They are not a universal solution for green infrastructure problems. Permeable paving or pavers should not be used within a 8-10 foot zone of a structure that has a basement or a concrete foundation. Water moves to where water isn’t. It takes the path of least resistance. Every site is different and needs to be tested and viewed as an original/unique new project opportunity and not as some standard project that requires a standard approach or the application of the latest industry craze.

I know this does not answer all the questions people had—mainly about snow. But maybe we can take care of those in comments. And I’ll tell you my take. To me, the whole question of pavers was kind of a moot point, given the bioretention system that Dave installed to handle storm water. He was able to find a good solution that would help sustain plants all around the lot—a big priority for the owner—for probably less money. And she’s getting a garden, not just paving.

Posted by on November 10, 2015 at 9:46 am, in the category Gardening on the Planet, Unusually Clever People.
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7 responses to “The question of permeable pavers and paving”

  1. Laura Munoz says:

    I never thought to question Dave’s use of concrete.

    I always thought concrete was impenetrable to moisture until my experience with the concrete floor of a garage. Two to three days after a rain, it was wet/moist. I’ve read that regular concrete–depending on the mix and location–is indeed, porous even though I always thought otherwise. I guess wet basements are a testament to this in some instances.

    Last month, I installed (in the south where there is little to no frost heave) a clay brick paver pathway on sand between old growth trees. It was a short expensive pathway. I can’t imagine the cost on a larger scale especially having to accommodate frost heave to make the product function appropriately.

  2. Something else I hope people consider is how accessible those options are. I don’t have any experience with the surface of permeable concrete, but pavers can be tricky or even dangerous for someone using any sort of assistance device (wheelchair, walker, etc) given gaps and uneven surfaces. A dentist’s office is going to see people from all stages in life and should be accessible for everyone.

  3. anne says:

    The pavers are interesting visually, but I would have to nix them in my area because it freezes and snows here, and as Octopusgallery notes, accessibility issues.

    Many years ago, before anyone thought of these things, our neighbor re-paved her driveway with permeable aggregate concrete (had lots of colorful pebbles included), skillfully leaving 3×4 spaces in a pattern throughout in spots cars would park over. These she planted with ornamental strawberries, and they thrived despite regularly being parked over and presumably having oil and car dirt dripped on them. It looked nice, and was not slippery to walk on.

  4. I was pretty hyped when my neighbor decided to remove their pavers and get concrete. We hauled those pavers right over to my raised beds and made a pathway. I’m stoked. No one getting too muddy in the garden. Nice pathway. Yippee skippie. Love upcycling.

  5. Most of my reccs and experience is on projects wherein I have to be cognizant of budgets and resource consumption and efficiency…. But most of what is TRULY sustainable and regenerative and environmental. Permeable paving is but a “tool” in the green infrastructure “tool box”. It can be applicable and work in some situations but should not, like ANY other Green Infrastructure “tool” be relied upon as the cure-all and fix for any runoff challenges.

    I have said this so often: Each site is DIFFERENT and requires independent thinking and assessment and creative engineering and desing and implementation. There shoule be NO generalized generic Rule Book that dictates how a project or site should be developed or redeveloped. That is the EASY way and LAZY way out!

    Get your hands dirty and knees bloody and you will learn so much! Take the CAD program outside and help implement it to maybe learn more smarter and better and cheaper and efficient methods to implement these systems.

    Shut the TV, and the “Smart?” Phone and the Computer off. Get out and do it!!! There is no substitute for being on site and physically implementing and managing the development of these systems. None.

  6. anne says:

    Dave, your comments about budgets, resource consumtion and efficiency really rang true to me. Being a farmer, I often think that most people don’t truly understand the limits that we face, versus the ideals we strive to achieve. The reality is that most consumers are paying you to do what they can’t, or won’t. We hope they want to pay for our values.