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Permeable paver installation best practices make all the difference in performance

August 31, 2012

A college campus in Florida, a parking lot in Maryland, a street in Ohio, a park in North Carolina, all described here in Pathway Café. Hundreds of miles separate these installations of StormPave® permeable pavers, but each has one thing in common: Each has been deluged with heavy rain.

Permeable pavers are part of a rain garden on the campus of North Carolina State University in Raleigh.

The rain hits the bricks, then disappears, because each one of them has two parts working together: the StormPave® paver, and a best management practices installation underneath.

Recently, however, we’ve seen stories about permeable pavers being incorrectly installed with gravel and sand. We don’t recommend it. While conventional pavers do call for installation using crusher run and sand, permeable pavers do not. That’s because even though the permeable pavers are specifically designed to have enough space, called voids, between them to let the rainwater in, the rainwater needs to have a place to go.

Imagine a glass aquarium. Put a layer of big rocks in, then layers of progressively smaller rocks, almost to the top. Put StormPave pavers across the top. Now, get a garden hose out and start spraying water atop the pavers.

The water will flow across the pavers, down through the gaps in between, first to the small rocks, then to the big rocks, at the bottom of the aquarium. If you leave the hose running, then it will eventually begin filling the aquarium. The rock layers do two things: They hold up the pavers, while providing a place to store the water. If this was an actual installation, the water would seep into the earth in a day or so. And if this was an actual rainstorm, chances are the rain would stop before the system filled up with water and overtopped the pavers. That’s because a best management practice system calls for 18 inches of open-graded aggregates without fine particles.

If you have a rainstorm that can fill 18 inches of space before it begins to dissipate into the ground below, that’s either a fire hose or a rainstorm of Biblical proportions.

Specifically, the recommendation is for 12 inches of #2 stone, followed by four inches of #57 stone and two inches of #8 or 89 aggregate. The pavers go atop that and more of the #8 or 89 aggregate is swept in between them.

Topography and usage can vary somewhat from that. A residential patio or walkway will need less of a foundation than a driveway or a city street, because of the weight it will bear.

Contact an engineer for your project, or call on Pine Hall Brick Company.

We’ve seen projects work, even in the face of approaching hurricanes, when these practices have been followed. We can’t say they will work when they aren’t.

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