The greening of the driveway

Driveways might not be the most glamorous feature of a home, and many people probably take them for granted — until they crack or otherwise require an expensive makeover.

Otherwise one might not consider replacing the drive with a new version. But if it comes to that, there are a lot of interesting options, some of which are a lot more sustainable than what’s probably there now.  

Grass, seashells, hemp-based bricks and solar panels represent a new generation of driveway surfaces, one that takes a more eco-friendly approach to a utilitarian home amenity.

The wildest idea calls for seeding the area with fungi, though that grow-your-own version is in the future. The idea is that those mushrooms will grow into a hard surface, not a side dish for dinner.

Asphalt and concrete are old school bad boys

That harmless-looking strip of concrete or asphalt that drivers use daily can be an environmental hazard. Why? Any solid, impermeable surface will send excess rainwater into sewers instead of letting it filter through the ground.

This puts added pressure on water systems and can worsen what is called nonpoint source pollution. When rainwater passes through gutters and downspouts and onto a driveway with an impermeable covering, it picks up traces of petroleum, grease and pesticides, delivering them to the storm drain — and eventually on to local rivers, lakes, or the ocean.

Water that passes through the soil is filtered before it enters an underground aquifer or another water source. Tiny organisms in the dirt eat and digest the pollutants, and the soil can also prevent the runoff from causing erosion of waterways downstream.

There is not good . . . and then there’s worse. A Washington Post article said that  “concrete is one of the least environmentally friendly choices for a driveway.“

Concrete manufacturing produces harmful carbon emissions and other pollutants, though asphalt is even worse. First, it’s a stew of oil and other petroleum byproducts (with eco-unfriendly drilling and processing before it is delivered). Like concrete, it doesn’t allow rainwater to be filtered as it reaches the water table below ground.

These types of driveways are relatively inexpensive (about $5 a square foot for concrete, about $3 for asphalt) and fairly easy to maintain, so it’s easy to see why they remain popular.

While bricks seem like a less damaging option, they’re fired in high-energy kilns. They’re often installed with mortar and are then as impervious as the other types of surfaces. (Laying them with sand or dirt is an improvement because it lets some water through.)

But there are now a variety of alternative, eco-friendly driveway materials in the pipeline.

The environmentally sensitive driveway

There are lots of choices in the greener driveway department. Most fall under the appealing acronym SuDS (sustainable drainage systems) because — as the name suggests — they allow water to permeate. Some are complex and elegant, while others are more low tech and “greener” looking.

“By allowing the rainwater to flow naturally back into the ground, they reduce pressure on stormwater systems, and prevent water and pollutants from flowing back into our rivers and streams,” says Joe Raboine, director of Residential Hardscapes at Belgard, an Atlanta-based company that makes permeable pavers and other solutions.

Here are 7 of the most popular — and weirder — options for a green driveway:

1. Gravel

Gravel is an inexpensive and highly eco-conscious choice. It can cost as little as $1 a square foot (but almost double that in some regions), so it’s especially cost-effective for longer paths.

The gravel itself can often be sourced locally (green bonus points!) and is super porous. Recycled gravel is even available in some places — sometimes made from ground-up concrete — for a kind of environmental trifecta.

One caveat: gravel is not a great choice in cold climates that get a lot of ice and snow because it can mix with them and make plowing more difficult — plus a fair bit of the gravel mix can get carried away in the shoveling or plowing process, resulting in the need for replacement stone in the spring.

Gravel can also be noisy, so it alerts the neighbors to a person’s comings and goings.

2. Seashells

Maintain that beachy feel year-round with another strong contender. Shells can be harvested without damaging the shoreline, and they are then processed into a durable mix that’s very porous.

Depending on the treatment, the shells will, at first, retain their shape and color, while others will be ground into smaller pieces. Over time, the shells break down and supply nutrients to the surrounding plant life.

This type of driveway can cost less than $1 a square foot, so it’s another great option for large surfaces. It’s not readily available in all regions and can be painful to walk on barefoot.

3. Permeable pavers

An attractive and arguably more traditional treatment than some others, the title is a bit of a misnomer. The pavers themselves are solid, but the system is highly permeable. According to Raboine of Belgard, the process works like this:

“Permeable pavers are designed to allow water to run through the space between pavers instead of running off the surface of the pavement into a catch basin or drain. These joints are filled with clear crushed stone so that the water flows freely.”

The process assure water is filtered before it re-enters the water table.

“Below the pavers is another layer of clear stone (no fine particles) anywhere from 8 inches to over 1-foot-thick depending on application and soil conditions,” he added. “From here the water can seep back into the ground slowly, and naturally.”

It runs from about $15 to $30 per square foot. Visit belgard.com for more information.

4. Grass

A driveway composed of regular grass would quickly become a muddy mess. But with a system of curvy plastic supports buried in the soil, that turf can support tons per square meter and stay relatively lush.

The systems allow rainwater to flow pretty much as it would through a regular lawn. Some grids have perforations that allow water to also flow laterally to prevent pooling. The GD Grass system website has lots of detailed information.

5. Solar

The applications for solar panels continue to expand, so what was once a roof-only situation can now be found on house siding and even walkways and driveways—and beyond. Eventually, many road, parking lot, and other large surfaces could incorporate solar panels, generating power for local municipalities. For the individual consumer, a solar driveway can generate clean energy and lessen the dependence on other (possibly less sustainable) sources.

Comparatively more expensive than other methods here, the cost of this technology should come down as it becomes more widely used and produced in greater quantities. A system’s cost varies based on 1) how much energy one needs/wants this installation to create, and 2) how much ground real estate one has to work with.

Long-term costs/benefits also vary depending on location. A driveway in Arizona receives more sun than one in Minnesota and will therefore produce more energy, recouping costs more quickly. Also, one of these systems makes more sense if there aren’t four cars parked in the drive for most of the day.

Solar Roadways is one example of a solar provider addressing the needs of their client base. The Idaho based company makes solar road panels, which includes heating elements to prevent snow and ice accumulation.

And there’s more. “LED lights can be used for holiday decorating and entertaining. This also means that driveways can double as sports courts, as the LED lights can be programmed to make various sport court options,” says Julie Brusaw, Co-Founder of Solar Roadways.

6. Hemp

One of the newer and more innovative products in this arena are hempcrete bricks, which are made from tough inner hemp fibers and a lime-based binder, which allows them to keep their shape even after years of weathering.

They are generally lighter than regular bricks, which makes them less expensive and more environmentally sustainable to transport. They also absorb carbon from the atmosphere, so it’s like having extra trees added to a property.

The legality of hemp has not been definitively decided in all states, but the future looks promising.

8. ‘Shrooms

Grow your own. This is one of the stranger (and least developed) ideas, but one that’s gaining traction. The basic idea is that an organic substrate is inoculated with mycelium, a network of fungal threads. These then eat and digest the substrate and, in the process, form a solid mass.

According to the site Critical Concrete, this mycelium mass has several advantages:

“The advantages of using fungal mycelium lie in the fact that it is 100% biodegradable as well as in its exceptional material properties. More specifically, the mycelium tissue can trap more heat than fiberglass insulation, it is fireproof, nontoxic, partly mold and water resistant and stronger pound for pound than concrete.”

Construction companies are working to make the process more practical and devising ways to turn the mass into bricks and other materials that have consistency.

The  process of growing the mushrooms can be manipulated to create just about any shape. An article from 2018 in Critical Concrete details some of the promise of “mycelium technology” and how it can be employed to solve various construction problems.

Phil Ross, a San Francisco–based artist and the chief technology officer and cofounder of MycoWorks, is one advocate who sees the possibilities of fungi. His company grows mycelium into art, furniture, and durable fabrics, including a leather substitute. (Not surprisingly, his nickname is the “Mushroom Man.”)

The technology (if it can even be called that yet) is still being developed, but the advent of mushroom-surfaced driveways may not be far off.

‍