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.)
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.
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.
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.