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What is the most eco-friendly type of driveway? Brick, gravel, black driveway sealant? —Izzy Lasch-Quinn
The eco-trend in driveways can be summed up in a word: Unsealed. The greenest driveway is permeable, or pervious, which means it allows water to drain into the soil beneath it. The least green driveways are hard, continuous surfaces, such as impermeable concrete, asphalt and/or black driveway sealant, off of which rain and wastewater run freely into storm drains. In addition to wasting water, this promotes flooding and erosion, and carries pollutants, such as pesticides and oil, into our waterways.
Hard blacktop should also be avoided because it’s a heat sink that raises the temperature of surrounding areas. As with painting your roof white, lighter colored surfaces reflect and disperse heat.
Here are some green options to consider:
Pavers, such as bricks, concrete blocks, or stones, make for an eco-friendly driveway so long as the cracks between them are left unsealed. You can even plant grass, moss or other plants between the pavers—or just let weeds do their thing. Aqua-Loc concrete pavers are blocks that are attached in a network, leaving small spaces in between. Pavers can be set in a bed of gravel or sand, but Aqua-Loc employs a rather complex but highly supportive permeable underlay of stone blocks, chips, and gravel. (Check out Hanover Pavers for more info.)
Open-cell concrete blocks, another form of pavers, are greener still because they are hard-walled frames with empty centers that allow much more space for drainage. The spaces should be filled with gravel or sand, and grass seed or sod can be layered over. My neighbor down the street did this years ago, and it looks beautiful.
Geoblock is an inexpensive option that can be laid on existing grass without any gravel/sand filler. Learn more at Presto Geosytems.
Gravelpave2 and Grasspave2 are made of a grid of plastic rings connected with a porous fabric and set in a base of unsealed sand or gravel. The spaces in the rings can be filled with gravel, grass seed, or sod. For more info, check out Invisible Structures. In a similar vein, Permaturf uses rings made of 100 percent recycled polyethylene.
Permeable/porous concrete, although it sounds like an oxymoron, is a surface deemed green by no less than the U.S. Environmental Protection Agency (EPA). This all-in-one, continuous pavement is actually a mix of small stones held together by cement that is riddled with pockmarks that allow for an absorption. "Think of an English muffin," says Rick Goyette, an expert for the U.S. Green Building Council’s Green Home Guide. (Check out the photos on the Pervious Pavement website.) There’s also permeable pavement made out of 100 percent recycled glass, from Presto Geosystems. Because it still qualifies as a rigid surface, permeable concrete holds up well to a snow shovel in cold climates, Goyette notes.
Caution: Driveways are not a DIY project. You will need a building permit and leveling the ground and laying the sand/gravel base, is best left to a professional. Ask the companies above for referrals to contractors in your area.
For some inspirational photos of bucolic green driveways, visit the Chic Ecologist.