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How Do Permeable Pavers Work?

Permeable pavers are becoming a popular choice, especially in Northern Virginia. As local governments have become more concerned about stormwater management, they’ve clamped down on the amount of runoff that leaves your property. If your total square footage of impervious surfaces exceeds the percentage allowed (they typically include homes, garages, sheds, pools, patios, and driveways), you either have to scale back your project, install a rain garden, or utilize permeable pavers.

Calling them permeable pavers, however, isn’t 100% accurate, as the water does not penetrate the paver itself. Rather, the pavers are designed to have gaps between them that allow water to pass through into the soil. An effective installation is all about the base.

Installation methods vary by manufacturer, and you should always follow their directions or those of a local soil engineer. This is what Techo-Bloc recommends in their installation instructions for the Permea paver:

  • Excavate to the required depth (base + bedding layer + paver thickness)
  • Place a layer of geotextile fabric on the soil to prevent soil particles from migrating into the base stone
  • Install a minimum 6″ deep layer of 3/4″ clean aggregate (in VA, it’s sold as 57 stone) and compact
  • Place another layer of geotextile fabric atop this aggregate base
  • Install a 2″ layer of 1/4″ clean stone (sold here as #8 stone) and compact
  • Lay the pavers per the manufacturers instructions, setting them hand tight (lugs will act as spacers)
  • Install border pavers
  • Install curbing or edging blocks
  • Install 3/8″ stone between the joints
  • Compact the entire patio

So what’s the big deal if you go off script and lay permeable pavers like you would standard pavers? Well, for starters, you’re likely to get some uneven settling from improper compaction (remember my post about problems with paver patios?). You’ll also get a patio that won’t allow water to flow through it. A standard patio base is 21A or crusher run- an aggregate mix with a variety of particle sizes all the way down to “fines.” When compacted, all these particles lock together, and good luck getting water to drain.

The good news is that the paver manufacturers see the direction the market is headed, and have provided thorough documentation for how to use their pavers. If you’re installing the pavers yourself, just do what they say. If you’re hiring someone, ask them what materials they’re using. If they mention 21A or sand, it’s time to find a different installer.

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