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This blog was born out of our passion for "green" design, our continual pursuit of new innovative sustainable technology, and our commitment to learning and growing as professionals. We will be researching and discussing a new topic related to sustainable practices frequently, so check back with us often.

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Friday, September 10, 2010

Permeable Pavement Systems

Just recently, VDC hosted a lunch & learn at their office in downtown Asheville, showcasing Belgard paving systems. The main topic of the presentation was Sustainable Site Design & Stormwater Management with Permeable Pavement Systems and there was some great information on paver systems. Below is a general overview of what pervious pavement is, its benefit and several types of systems used today. There is also some great information related with permeable paver systems such as freeze thaw, maintenance & life cycle cost comparisons located here: http://atfiles.org/files/pdf/PermPavers.PDF

Pervious pavement is designed to allow percolation or infiltration of stormater through the surface into the soil below where the water is naturally filtered and pollutants are removed. This helps promote growth in trees and flower beds that are near the system. In addition to these benefits, it also cleans the water that drains into the natural waterways of our cities and neighborhoods and in some cases it can be used to help reduce the amount of stormwater retention and drains throughout a city by reducing the total volume of stormwater runoff and helping to remove the oils, fuels and other contaminants that are normally picked up by water on its way through the streets.

In contrast, normal pavement is an impervious surface that sheds rainfall and associated surface pollutants forcing the water to run off paved surfaces directly into nearby storm drains and then into streams and lakes.

These contaminants can kill not only vegetation throughout the city, but wildlife that drinks from the streams and rivers which is fed by this drainage fallout. Many wildlife species are in danger of becoming extinct due to their short life cycle.

Types of Pervious Pavement

Pervious/Permeable Pavers: This material can be used to create a porous surface with the aesthetic appeal of brick, stone, or other interlocking paving materials. They are most often used for driveways, entryways, walkways, or terraces to achieve a more traditional, formal appearance.

Permeable pavers are an environmentally friendly and attractive alternative to traditional paving methods. Unlike standard concrete, asphalt or even paver installations, permeable paver installations provide for drainage and filtration of water into underlying soils or water storage system. Permeable pavers allow water to percolate through joints or holes in the paver itself but also provide a solid surface that can withstand weight loads that are comparable to those of standard concrete or asphalt surfaces.

Permeable pavers come in many designs, and may be made from concrete, plastic or even combinations with recycled rubber. These pavers can be used for in many commercial and any residential paving application including patios, walkways, driveways, and parking lots.

Potential LEED credits for Permeable Pavers

Porous Asphalt: A great advantage to porous asphalt is that the same mixing and application equipment is used as for impervious asphalt. Only the formula for the paving material changes with porous bituminous pavement. For more details on the various layers of materials see, the Pennsylvania Stormwater Management Manual Porous pavement specification used by the City of Seattle Washington Park Department. The amount of asphalt binder required is about 6% by weight which is somewhat higher than required for standard impermeable asphalt mixes.

Bituminous permeable paving is appropriate for pedestrian-only areas and for very low-volume, low-speed areas such as overflow parking areas, residential driveways, alleys, and parking stalls. Permeable paving is an excellent technique for dense urban areas because it does not require any additional land. With proper design, cold climates are not a major limitation.

Porous Concrete: Again, the same equipment may be used as for standard concrete. Larger pea gravel and a lower water-to-cement ratio is used to achieve a pebbled, open surface that is roller compacted. This material was recently used in a parking area in Fair oaks, California as a way to reduce solar heat-gain solar from absorption. Project costs were reduced because no retention pond or connection to the municipal storm drain system was required.

Plastic or Concrete Grid Systems: High strength plastic or concrete grids (often made from recycled materials) filled with soil and planted with turf grass or a low-maintenance groundcover. Water passes through the turf block into a reservoir base of crushed aggregate, then infiltrates into the subgrade. Some are designed to be filled with gravel on top of an engineered aggregate material as well.

The grids provide a support structure for heavy vehicles, and prevent erosion. After heavy rains, the grids act as mini holding-ponds, and allow water to gradually absorb into the soil below.

Loose aggregate such as uniformly sized crushed stone can provide porous paving, although it is only suitable in light-traffic applications where it won’t quickly be displaced, ground down, or mixed with organic matter. Soft materials such as chipped bark or crushed seashells may be used as porous paving in pathways. Conventional dirt roads use mixed aggregate, including fines, and are largely impermeable.

Information found at the NAHB Research Center