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Pervious Paving Materials

DEFINITION
CONSIDERATIONS
COMMERCIAL STATUS
IMPLEMENTATION ISSUES
GUIDELINES

  1. Installation
  2. Grass Requirements
  3. Use and Maintenance

CSI Numbers:

025 100


DEFINITION:

Pervious materials permit water to enter the ground by virtue of their porous nature or by large spaces in the material.


CONSIDERATIONS:

Water-pervious materials such as gravel, crushed stone, open paving blocks or pervious paving blocks for driveways, parking areas, walkways, and patios minimize runoff from those areas, as well as increase infiltration. Some pervious paving options can retain turf and carry autos and trucks evenly without creating tracks or other heavy traffic wear signs. Many pervious surfaces that receive auto traffic require a clay-type roadbase subgrade. The roadbase material could slow water percolation in heavy rains and cause over-saturation above it, leading to puddles or runoff. It is best to select a pervious paving material that can use the most porous subbase. Care should be taken during installation to minimize excessive soil compaction.

A turf covered pervious surface can be problematic for certain types of footwear, and can stay wetter after rains due to the height of the grass. A compromise approach is to retain a small impervious walkway to accommodate the areas that provide access to vehicle loading and unloading.

Pervious materials will cost more than asphalt surfaces with some systems costing as much as 40% more. If used in areas with underground utilities needing repair, pervious paving materials can easily be removed from only the repair area. Pavement replacement is simplified and expensive measures such as asphalt cutting are eliminated.

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Pervious Paving Satisfactory Satisfactory in most conditions Satisfactory in Limited Conditions Satisfactory Satisfactory Satisfactory in most conditions
Satisfactory Satisfactory
Satisfactory in most conditions Satisfactory in most conditions
Satisfactory in Limited Conditions Satisfactory in Limited Conditions
Unsatisfactory or Difficult Unsatisfactory or Difficult


COMMERCIAL STATUS

TECHNOLOGY:

Well-developed.

SUPPLIERS:

Several systems are presented in Sweets catalogue and can be accessed locally.

COST:

Can cost 10-40% more than asphalt surfaces.


IMPLEMENTATION ISSUES

FINANCING:

Available.

PUBLIC ACCEPTANCE:

Good; more product exposure needed.

REGULATORY:

The driveway approach is regulated by the Department of Public Works and Transportation. The area from the street to the property line must be concrete. Contact the Department of Public Works and Transportation to discuss possible alternatives.


GUIDELINES

1.0 Installation

Pervious paving will function best with a similarly porous subgrade. This can be difficult given the clay soils in our area, and compaction which may occur during the construction process.Contractors will need to take special precautions to prevent excessive compaction of the soil during the installation process.

Sediment should be prevented from entering the pore spaces of the paving blocks during and after installation. If the pore spaces of pervious paving become filled with sediment, the pervious nature of the finished product will be diminished.

2.0 Grass Requirements

Some pervious paved areas which will receive auto traffic may use interlocking pavers that have open spaces which allow grass to grow in the openings. This creates a surface combining good load-bearing capacity and large pervious openings.A subbase consisting only of sand and gravel will have less ability to support grass roots growing into it. This restricts the grass root zone primarily to the topsoil directly above the subbase, and thereby can be subject to more rapid drying out in drought conditions. It is preferable to use a subbase that includes soil in the mixture of sand and/or gravel. This will permit better growing conditions for the grass.

Cultivation of grass in interlocking pavers will be most successful in medium to low traffic areas.

Paving systems that have distinct ridges above the soil level can prevent the crown of the plants from being crushed.

Certain systems interlock and thereby avoid ruts, cracking, or settling occurring in heavily traveled spots. Very heavy loads can be displaced by the interlocking feature.

3.0 Use and Maintenance

Pervious paving areas can be used to facilitate groundwater recharge. Pervious paving can accept runoff from roofs and adjacent parking areas and allow it to infiltrate the ground. It can also reduce the need for curbs and gutters as drainage features.Proper maintenance of permeable paving includes periodic vacuuming of the paving to remove sediment buildup. Vacuum-type street sweeping equipment, as opposed to equipment which sweeps only, is the most effective.