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.

Causing Problems Downstream

With three cats, we’re always fighting the problem of every upholstered surface getting covered in fur. It doesn’t help that we have one black and two orange-and-white cats. When we saw the commercial for the Pledge Fabric Sweeper, we were excited. It looked like it worked great, and we would no longer blow through an entire lint roller getting the house ready for company.

The product does work great, but we were disappointed to discover that it’s a one-use, disposal product. Seriously, why? In the course of trying to find a similar product that you could reuse, I came across two creative option. First, you can modify a Pledge Fabric Sweeper so it can be emptied and reused. If that’s too hard, the commenters in that post had an idea that’s even more stupid-simple: stick the crevice tool of a vacuum between the rollers and suck the fur out. Awesome!

What does this have to do with landscape design? Our goal as designers is to not make the same mistakes that the Pledge product designers did. They solved one problem and made another one. Now, I understand that there are a number of factors that get considered when designing a product like this. In addition to “does it work?” there are considerations of what prices the market will bear, ease of packaging and shipping the item, and of course aesthetics. There’s also the issue of creating something at a moderate price that will actually need to be replaced pretty quickly.Which is fine from a short-term profit model (which is why I am so glad to be out of the corporate sphere), but these things are nice and bulky for the landfill.

When we’re looking at a landscape project, we face that balancing point of budget vs. longevity. I’m working with some folks right now who are debating materials for their driveway. Gravel’s the least expensive option, but it’s not particularly sexy and it gets in the lawn and the plant beds. Asphalt’s a step up but also not terribly attractive, and it presents its own maintenance issues. We’ve talked about stamped asphalt but can’t find a contractor servicing their part of West Virginia. The best option for a driveway is to do pavers closest to the house, but it’s also the priciest choice. It will also be their lowest maintenance choice, but my homeowners are regular people. They don’t know if they can comfortably spend the $30K this paver driveway might cost. That’s a decision that I can’t make for them; as their designer, all I can do is give them the options and the pros and cons of each approach.

As far as impacting the folks downstream from you, drainage is a huge consideration. The standard approach to stormwater management has been to get the water away from the house and off the property. I remember doing landscapes in San Diego, and the very first thing we did was trench 4″ lines from the downspouts and yard drains to the street. Problem solved! Except that this water flowed into the storm sewers, overwhelmed the treatment plants, and after any major storm the beaches in San Diego were closed because of raw sewage in the water. Just like the folks at Pledge, we were solving the problem right where we stood, but making a bigger problem for everyone else.

This is just one more reason why I advocate finding a good local designer, someone who understands your local soils, water issues, building materials and methods, and costs. Even the simplest design has a lot of moving parts, and it’s important to know how they affect one another- and your neighbors.

Where to Buy Pavers in Northern Virginia

Since we’re talking about pavers lately, I figured it may be useful to point out where they’re available to look at and purchase. I’m a big fan of display yards, where they’ve taken the time to lay a variety of paver styles and colors so you can see not only what the paver looks like in pattern, but also get a true sense of the color. Trust me, you never want to make your color selection based solely on a photo in a catalog.

One place that’s on my way into Manassas is the Stone Center (warning to at-work web surfers: their website has a video that starts playing as soon as the site loads. Don’t get fired). I stopped on my way home the other day to shoot some video of the EP Henry and Techo-Bloc display areas. Just FYI, the Stone Center also has a display area for Eagle Bay, which is a lower-priced line of pavers and segmental walls. And as the name implies, you can also buy a variety of stone products there- but that’s another post.