What are the green options for driveways?
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There are several factors to consider when defining a green driveway. Most often the factors depend heavily on the location, use and exposure of the site. Let’s outline some of the tenets which may individually or together define a driveway as green.
One issue with a paving surface such as concrete or asphalt is that it might be impermeable to water. The downside to impermeable surfaces is that they direct storm water to another location (such as the street) which essentially forces the municipal storm drain system to incorporate water that could have been absorbed on your property.
A lengthy discussion of why this is not optimal is beyond the scope of this response. Suffice to say that minimizing your impact on the surrounding municipal stormwater infrastructure will abate the opportunity for flooding, erosion, and transport of chemicals to undesirable locations where the stormwater is released. Therefore one aspect of a green driveway is permeability -- more permeability is greener.
A permeable driveway can be created in many ways. Pavers, permeable concrete, crushed stone and crushed seashells are the most popular. Given the fact that you will have to plow, snow-blow, or shovel during the winter months in NJ, crushed stone and seashells probably won't make the cut, but you still have many porous pavement options.
Heat Island Effect
Most people are aware that the temperature during the summer months is higher in city developments than in the rural countryside. While the buildings in the city certainly are a large contributor to this, the paved areas and streets surrounding those structures contribute in large part to the temperature difference.
These components absorb heat and radiate it to surround areas where the trees, grass and natural ground coverings shade the rural areas from being able to absorb heat in the same way. To combat the heat island effect, a green driveway would certainly take into account the overhead vegetative or structural shading and driveway color.
If you’ve spent any amount of time in a blacktop parking lot during the summer, it is obvious that the radiant heat has an impact on temperature and comfort. White concrete or lighter shades of gray have a significant impact on how much heat is absorbed and consequently radiated back into the air. Consider lighter shades of paving materials and planting trees to help define your green driveway to control the heat island effect.
After consideration of the principles above, it is prudent to discuss some of the materials, their positions in the "green pecking order" and other options given the region and climate of NJ.
- Asphalt: While I prefer to avoid a discussion of the definitions of asphalt, tar, or blacktop (that seem to be used interchangeably); I generally place any black paving surface at the bottom of the green pecking order. Aside from the fact that it does not support and in fact violates the green tenets listed above, can something that smells that bad really be green? Levity aside, this material is generally made using byproducts of the petroleum and/or coal industry. Someone could perhaps provide evidence as to why it is a greener option given the re-use of a waste material. However, I still wouldn’t recommend it as a green driveway option.
- Concrete: Despite my argument above, if you are considering a concrete driveway there is a coal byproduct that deepens the shade of green for a driveway install. Flyash is created by burning coal and can be used to strengthen concrete and decrease the carbon footprint of your project. Although the use of flyash will darken the color of your concrete, it could be offset by color additives.
- Pavers: I love the look and feel of a paver driveway when coupled with older architecture. Pavers provide permeability between joints as long as they are not sealed with polymeric sand or another water-sealing product. Consider allowing grass, moss or other groundcover to grow in the joints to prevent erosion and increase permeability. There is a maintenance burden not typically associated with a typical driveway. However, a light-colored paver driveway with vegetative joints and partial overhead shade would be considered a green driveway without question.
- Permeable/pervious concrete: I saved this material for last, as it will ultimately be my recommendation for your project. This permeable concrete is installed with voids that allow water a clear path to ground absorption. After seeing a demonstration of the product in which a glass of water traveled through 12 inches of concrete, I was sold. What a great decision -- after using it, I was just as delighted. Pervious concrete has a random surface look I associate with the nooks and crannies of a famous English muffin. These voids throughout the concrete provide the opportunity for water to make its way into the ground and provide the same rigidity as normal concrete surfaces. The product is available in light gray, which ensures that you are considering both tenets of a green driveway.
Typically, this permeable concrete is difficult to find because it requires certification of the installers. However, Salomone Redi-Mix in Wayne, NJ, is able to provide the concrete and professionally install it.
My first reaction to this product (before using it) focused on its durability and the ability to remove snow without damaging the surface. If you have similar concerns, have a look at this white paper that explains how the rigid nature of pervious concrete makes it less susceptible to damage from snow removal. It will also answer any questions you might have regarding maintenance.
Good luck on your project!
For more information:
Read Randy Potter's Q&A "I need to pave my driveway -- what material would you suggest?"