Better Site Design Fact Sheet: Alternative Pavers

Description

Alternative pavers are permeable or semi-permeable surfaces that can replace asphalt and concrete and can be used for driveways, parking lots and walkways. From a stormwater perspective, this is important because alternative pavers can replace impervious surfaces, creating less stormwater runoff. The two broad categories of alternative pavers are paving blocks and other surfaces including gravel, cobbles, wood, mulch, brick, and natural stone. While porous pavement is an alternative paver, as an engineered stormwater management practice, it is discussed in detail in the Porous Pavement Fact Sheet.

Paving blocks

Paving blocks are cement or plastic grids with gaps between them. Paving blocks make the surface more rigid and gravel or grass planted inside the holes allows for infiltration. Depending on the use and soil types, a gravel layer can be added underneath to prevent settling and allow further infiltration.

Other alternative surfaces

Gravel, cobbles, wood, and mulch also allow varying degrees of infiltration. Brick and natural stone arranged in a loose configuration allow for some infiltration through the gaps. Gravel and cobbles can be used as driveway material and wood and mulch can be used to provide walking trails.

Applicability

Alternative pavers can replace conventional asphalt or concrete in parking lots, driveways, and walkways. At the same time, traffic volume and type can limit application. For this reason, alternative pavers for parking are recommended only for overflow areas. In residential areas, alternative surfaces can be used for driveways and walkways, but are not ideal for areas that require handicap accessibility.

Siting and Design Criteria

Accessibility, climate, soil type, traffic volume and long term performance should be considered along with costs and stormwater quality controls when choosing paving materials. Use of alternative pavers in cold climates will require special consideration since snow shovels are not practical for many of these surfaces. Sand is particularly troublesome if used with paving blocks since the sand that ends up in between the blocks cannot effectively wash away or be removed. In addition, salt used to deice can also infiltrate directly into the soil and cause potential groundwater pollution.

Soil types will affect the infiltration rates and should also be considered when using alternative pavers. Clayey soils (D soils) will limit the infiltration on a site. If groundwater pollution is a concern, use of alternative pavers with porous soils should be carefully considered.

The durability and maintenance cost of alternative pavers also limits use to low traffic volume areas. At the same time, alternative pavers can abate stormwater management costs. Used in combination with other better site design techniques, the cumulative effect on stormwater can be dramatic.

Benefits

The most obvious benefit of utilizing alternative pavers includes reduction or elimination of other stormwater management techniques. Applied in combination with other techniques like bioretention and green parking, pollutant removal and stormwater management can be further improved. (See Bioretention and Green Parking Fact Sheets for more information.)

Limitations

Alternative pavers are not recommended for high traffic volumes for durability reasons. Access for wheelchairs is limited with alternative pavers. In addition, snow removal is also difficult since plows cannot be used, sand can cause the system to clog, and salt can be a potential pollutant.

Effectiveness

Alternative pavers all provide better water quality effectiveness than conventional asphalt or concrete and the range of effectiveness depend on the type of paver used. Table 1 provides a list of pavers and the range of water quality effectiveness achievable by different types of alternative pavers.

Costs

The range of installation and maintenance costs of various pavers is provided in Table 2. Depending on the material used, installation costs can be higher or lower for alternative pavers than conventional asphalt or concrete, but maintenance costs are almost always higher.

References

Bay Area Stormwater Management Agencies Association (BASMAA). Start at the Source: Residential Site Planning and Design Guidance Manual for Stormwater Quality Protection. BASMAA, San Francisco, CA. January 1997.

Center for Watershed Protection. Better Site Design: A Handbook for Changing Development Rules in Your Community. Center for Watershed Protection, Inc., Ellicott City, MD. 1998.

Schueler, Thomas R. Controlling Urban Runoff: A Practical Manual for Planning and Designing Urban BMPs. Metropolitan Washington Council of Governments, Washington, DC. 1987.

Schueler, Thomas R. Urban Runoff in the Washington Metropolitan Area. Metropolitan Washington Council of Governments, Washington, DC. 1983.

Smith, David R. Life Cycle and Energy Comparison of Grass Pavement and Asphalt Based on Data and Experience from the Green Parking Lot. The Heritage Conservation and Recreation Service, Order No. A-4331-4. 1981.

Smith, David R. and Sholtis, David A. An Experimental Installation of Grass Pavement. The Heritage Conservation and Recreation Service, Order No. A-4331-4. 1981.