Eco-friendly driveways turn down the heat.

From:
Mountain View Voice Mountain View Voice: Eco-friendly driveways turn down the heat (March 16, 2007)
Home & Garden - Friday, March 16, 2007


Eco-friendly driveways turn down the heat
Permeable surfaces under cars also help prevent toxic runoff to the Bay
by Katharine Lu

Although Sarah Carpenter had considered repaving their worn-out driveway with cement, the idea of a big chunk of it sitting in the front yard didn't seem to provide the most aesthetically pleasing, or environmentally friendly, solution.

Carpenter said she was not only concerned with the cement cracking over time, but with excess rainwater running off to one side of the house.

Instead, she and her family decided to go green and build a permeable-surface driveway. After Carpenter's driveway was flattened, a base level was prepared, and on the surface of that, interlocking 4-by-6-inch cement pavers and sand were neatly arranged in a geometric pattern.

Such "green" driveways are made of permeable surfaces that absorb rainwater and car pollutants, preventing them from running off into the storm-drain system — and ultimately polluting the Bay.

Carpenter said that with so many solid surfaces — including roads and sidewalks — on the ground already, green driveways are an excellent way to allow water to percolate back into the ground naturally.

"They're better for your property and neighbor by not having all the water pool to one side of the house. It just makes more sense, and they look nice," she said. "We can't make roads permeable, but driveways, pathways and parks can be. The more permeable surfaces we can use, the easier it is on the Earth."

If a cement paver ever becomes loose, Carpenter said, she simply scoops the dirt out and flattens the paver down again. She said she liked the idea so much that the patio and walkways in their house were converted to pavers and sand as well.

Cities come around

The idea took a while to catch on with local city governments. In Palo Alto for instance, previous city ordinances prevented homeowners from building non-cement or asphalt driveways. But in 2001, that city's council passed an ordinance allowing permeable materials, such as grass or gravel, to be used for residential driveways.

Bob Morris of the Public Works Department in Palo Alto said the city supports green driveways and encourages developers to prevent storm water runoff. He added that green driveways are ideal for decreasing the amount of water and pollutants in the storm-drain system.

"We didn't need to accommodate large volumes of water before; but as more buildings got built, there was more water runoff, overwhelming capacity in the storm system," Morris said. "We want to make sure the water that goes into storm drains is as clean as possible. The cleaner it is, the better it is for the fish, the Bay and the environment."

Besides controlling water runoff, green driveways also mitigate the "urban heat island effect," according to the Environmental Protection Agency's Web site. As an urban center grows, more and more concrete is used for parking lots, roads and buildings; as a result, solar heat reflects off the concrete, causing hotter air temperatures.

Driveways that use grass are an antidote to this, creating an air-conditioning effect by transpiring water back into the air.

For its part, Mountain View has no ordinances regulating driveway materials. (However, city law requires that at least 50 percent of a front yard be landscaped with a permeable surface not designed for auto use, said former city planning manager Whitney McNair.)

How to build it

Several methods and materials can be used to build green driveways. A common one is to arrange concrete pavers with 2-inch to 5-inch gaps set between them. The pavers are laid over a sub base and bedding layer, and on the surface, turf grows in the spaces, allowing water to seep into the ground.

Other approaches include grass and gravel pave. Grass pave, which looks like a regular lawn after it's been installed, is a honeycombed plastic grid that prevents root compaction. The grid is laid out over a base level, and a surface layer is spread out. The grass then grows up through the grid.

Maintained like a normal lawn, this method also prevents erosion. However, since there is a limit to how much weight and car-exhaust fumes the grass can handle, it's important to let the plants rest and regenerate from time to time.

Gravel pave works similarly, with a plastic grid set above a porous base. Most gravel driveways eventually compact over time, but usually the grid prevents the gravel from lodging in the soil sub-base.

Mark Maricinek of Greenmeadow Architecture designed a green driveway for a restored 1954 Eichler in Palo Alto. To transform the concrete jungle in the front of the house to something a bit greener, Marcinek set 12-inch concrete pavers four inches apart. Grass now grows in the gaps.

He suggests that those interested in converting their driveway to a permeable surface consider hiring a landscape architect or designer. "It's important to look at the drainage and the base for car weight; otherwise, the car will be sinking in the mud from the weight," he said.

There is one down side, however: Homeowner Norman Adams said people often mistake his grass driveway for a regular lawn. He now keeps orange safety cones handy in case the neighborhood gets busy and people park in front of his driveway.

This story originally appeared in the Palo Alto Weekly, the Voice's sister paper.

Comments

Posted by Phil, a resident of the Cuesta Park neighborhood, on Oct 26, 2009 at 8:11 am

I saw a new product at the West Coast green show in San Francisco that would be great for a driveway or any hardscape surfuce.This is a paver that is permeable and lets the watergo through the paver and into the ground below. This paver is actually porous and does not have gaps between the pavers. This paver is called EKOPAVER and I understand it is being used around the Bay Area.If you google EKOPAVER information can be found.
Report Objectionable Content