Permeable Pavers

I wanted to put in a small paved area between the beds in the back for the grill and a sitting area.  In keeping with the theme of environmentally friendly landscaping, i opted for a permeable system.  Traditinal paving stones use rock dust as a base, have tight fitted joints swept full with fine sand.  Water can neither flow through the joints nor the base, running off the surface and into the storm drain.

D.C. has about 37% of its area inpervious to water, mostly buildings, roads and parking lots.  Where does that water go?  A majority of it ends up in the rivers since most road and parking lot drains connect directly to the watershed, taking with it all the contaminates from cars, trucks, fertilizers, pesticides, trash among other things.

Also, since DC is a combined sewer system, if there is a “significant” rain, the treatment plant simply dumps what it can’t treat into the watershed.  That’s right:  untreated sewage diluted with street runoff goes straight to the rivers.  You can see how much rainfall leads to amount of sewer overflow for your area of DC.  The frightening thing is that it doesn’t even need to be a heavy rain: some areas of the system can only handle .1 inch of rain before it overflows.  Georgetown, for example, has an average of 73 overflow events every year!  Yum.

Alright, enough soap boxing, show us what you did!

To cut costs and footprint, i got used bricks off craigslist: 20 cents each instead of $1 each new.  Dug down to a level depth of 11 inches: 7 inches of 3/4″ rock, 2 inches 3/8″ rock, 2″ for the height of the brick.  This deep base will act as a water trap and allow time for it to enter the soil. Tamp it down as you go as the finished product is only as good as the base you put it on!  It’s vitally important to use angular rock since it settles and packs much nicer than rounded rock, which tends to stay loose, allowing the bricks to wobble.

3/4" blue stone (#57 rock)

3/8" Chips (#8 rock)

Make sure you have a nice level surface before laying the bricks.

 Another key difference in this

type of paving is to lay the bricks with a larger gap, mine were 1/2″ apart, then fill this gap with a permeable aggregate (the 3/8″ chipped rock).  This allows the water to flow in between the bricks and into the lager stones underneath.  You CAN’T use pea gravel, as the round rock does not settle making for loose joints.  Spike in the plastic brick boarder to keep everything in place, and sweep in the extra 3/8″ rock chips into the joints.  For heavier traffic areas or driveways, you’d probably want to get an interlocking block designed for permeable paving.  Make sure you test how permeable your soil is before you decide on what system works for you: i have sandy soils, so i don’t have to worry about standing water.  I’ll post a finished photo when i’m done just need to get a little more stone for the joints…


About Ryan

Urban gardening at it's best (sometimes it's worst)! Adventures and learnings from going 100% lawn free in a D.C. row house.
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