Permeable paving

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Conceptual diagram illustrating an adjustable storage underdrainA perforated pipe used to assist the draining of soils. configuration beneath permeable interlocking pavers

Overview

Permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. allows stormwater to drain through the surface and into a stone reservoirAn underlying aggregate material bed that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe., where it infiltrates into the underlying native soilThe natural ground material characteristic of or existing by virtue of geographic origin. or is temporarily detained.

The following are different types of permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.:

  • Permeable interlocking concrete pavers (PICP)
  • Plastic or concrete grid systems
  • Pervious concrete
  • Pervious asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

Permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. is ideal for:

  • Sites with limited space for other surface stormwater BMPs
  • Projects such as low traffic roads, parking lots, driveways, pedestrian plazas and walkways

The fundamental components of a permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. system are:

  • interlocking blocks with infiltration spaces between
  • Precast pervious slabs or pavers
  • a cast in place surface without finesSoil particles with a diameter less than 0.050 mm., so that the finish is pervious to water
  • a bedding course to stabilize the surface
  • underground storage layer of aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Additional components may include:

Planning considerations

Permeable pavements are surfaces that encourage infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.. They can be used in place of conventional asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. or concrete pavement. These alternatives contain pores, spaces and joints for allowing stormwater to pass through to a stone base, where it infiltrates into underlying native soils or is temporarily detained. Types of permeable pavementAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. include:

  • Pervious concrete
  • Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.
  • Permeable interlocking concrete pavers (PICP, or just permeable pavers)

Geometry and Site Layout

Parking lot with perforated pavers in stalls only, Singapore

Permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. can be used for entire parking lot areas or driveways and can be designed to receive runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from adjacent imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. surfaces. For example, the parking spaces in a parking lot may be permeable pavers while the drive lanes themselves are imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.. In general, the imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. area should not exceed the area of the permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. which receives the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.. A hybrid permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil./infiltration chamber design can feature connection of a roof downspout directly to the stone reservoirAn underlying aggregate material bed that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. of the permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. system, which is sized to store runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from both the pavement surface and the roof drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds..

PretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

In most designs, the surface acts as pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. to the stone reservoirAn underlying aggregate material bed that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. below. Periodic vacuum sweeping and preventative measures like not storing snow or other materials on the pavement are critical to prevent clogging. Another pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. element is to have a choking layer above the coarse gravel storage reservoir.

Landscaping

Landscaped areas must drain away from permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. to prevent sedimentsSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. from running onto the surface. Urban trees will benefit from being surrounded by permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. rather than imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. cover, because their roots receive more air and water. Interlocking pavers used around the base of a tree may be removed as the tree grows.

Risk of Groundwater Contamination

  • Stormwater infiltration practices should not receive runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from high traffic areas where large amounts of de-icing salts are applied (e.g., busy highways), nor from pollution hot spots (e.g., source areas where land uses or activities have the potential to generate highly contaminated runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. such as vehicle fuelling, servicing or demolition areas, outdoor storage or handling areas for hazardous materials and some heavy industry sites)
  • Prioritize infiltration of runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from source areas that are comparatively less contaminated such as low traffic roads and parking areas.

Heavy Vehicle Traffic

Many types of permeable surface are certified to ASSHTO-25, including PaveDrain PICP type paving, LSRCALake Simcoe Region Conservation Authority headquarters, Newmarket, ON

Permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. is not typically used in locations subject to heavy loads. However, some permeable pavers are designed for heavy loads and have been used in commercial port loadingThe total mass of a pollutant entering a waterbody over a defined time period.The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration. and storage areas.

Setbacks from Buildings

Permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. should be located downslope from building foundations. If the paving does not receive runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from other surfaces, no setback is required from building foundations. Otherwise, a minimum setback of 4 m down-gradient from building foundations is recommended.

On Private PropertyLand owned by private individuals or companies.

If permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. systems are installed on private lots, property owners or managers will need education on their routine maintenance needs, understanding the long-term maintenance plan. They may also be subject to a legally binding maintenance agreement. An incentive program, such as a storm sewer user fee based on the area of imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. cover on a property that is directly connected to a storm sewer, could be used to encourage property owners or managers to maintain existing practices.

Design

Finish course

Consult the manufacturer for the design specifications of their product. In pervious concrete and porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. systems, the concrete or asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. mix specifications and construction procedures are key to proper functioning. These systems require well-trained and experienced contractors for installation.

Specifications for pervious concrete, porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces., and permeable pavers
Material Specification Quantity
Pervious concrete
  • 28 day compressive strength = 5.5 to 20 MPa
  • Void ratio = 14% - 31%
  • Permeability = 900 - 21,500 mm/hr
Thickness will range from 100 mm - 150 mm depending on the expected loads
Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.
  • open-graded asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. mix with a minimum of 16 % air voids
  • Polymer can be added to provide additional strength to heavy loads
Thickness will range from 50 mm - 100 mm depending on the expected loads
Permeable pavers
  • ASTM No. 8(5 mm dia) crushed aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. is recommended for fill material in the paver openings.
  • Pavers shall meet the minimum material and standard specification for precast concrete pavers.
  • Pigment in concrete pavers shall conform to ASTM C 979 ACI Report No. 212.3R provides guidance on the use of pigments.
  • Maximum allowable breakage of product is 5%
  • For vehicle applications the minimum paver thickness is 80 mm
  • For pedestrian applications is 60 mm and joint widths should be no greater than 15 mm.

Foundation aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Geogrids like these are sometimes incorporated into the layers of permeable pavementAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. foundation aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. to provide additional stability

Most OPSS aggregates are not recommended for use in permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. systems. The exception being type 'o' with a default void ratio of 0.3.

GeotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

Geotextiles are not always necessary and may be prone to clogging. Consider using courses of finer aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. or sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. instead.

Sizing stone reservoirs

The stone reservoirAn underlying aggregate material bed that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. must meet both runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. storage and structural support requirements. The bottom of the reservoir should be level so that water infiltrates evenly.
If the system is not designed for infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., the bottom should slope at 1 - 5% toward the underdrainA perforated pipe used to assist the draining of soils..

Permeable paving: Sizing

Modeling permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. in the Treatment Train Tool

Permeable paving: TTT

Gallery

Landscaping and grading

Landscaped areas must be graded drain away from permeable pavingAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. to prevent sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. from running onto the surface.
Urban trees benefit from being surrounded by permeable pavementAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. rather than imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. cover, because their roots receive more air and water. Block pavers around the base of a tree can be removed as the tree grows.

Performance

Starting after TRIECA (end March) members of STEP will be undertaking a literature review on the performance of our most popular BMPs. The results will be combined with the information we have to date from the development of the Treatment Train Tool and agreed performance metrics established. Until then, please feel free to continue to ask questions via email or the feedback box below.

Permeable pavers can be classified into two categories according to the infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. of the underlying subsoil:

  • Full InfiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.: Full infiltration designs are more effective, because little if any of the pollutants generated on the impermeable surfaces leave the site as surface runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.
  • Partial InfiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.: Partial infiltration designs with underdrains generate more runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.

Studies in North Carolina have shown the average curve number of permeable pavements to range from a low of 45 to a high of 89. [1]
Partial infiltration designs with underdrains generate more runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface., and as a result, are often used in studies investigating the water quality impact of permeable pavements on surface waters. These studies show load reductions above 50% for total suspended solids, most metals and hydrocarbons [2][3]
As with all stormwater infiltration practices, risk of groundwater contamination from infiltration of runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. laden with road de-icing salt constituents (typically sodium and chloride) is a significant concern. Chloride ions are extremely mobile in the soil and are readily transported by percolating water to aquifersLayer of rock or soil that holds or transmits water..

Construction Considerations

Construction of permeable pavementAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. is a specialized project and should involve experienced contractors. The following general recommendations apply:

  • SedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. Control: The treatment area should be fully protected during construction so that no sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. reaches the permeable pavementAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. system and proper erosion and sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. controls must be maintained on site.
  • Weather: Porous asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. and pervious concrete will not properly pour and set in extremely high or low temperatures [4]. One benefit to using permeable pavers is that their installation is not weather dependent.
  • Pavement placement: Properly installed permeable pavementAn alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil. requires trained and experienced producers and construction contractors.

Inspection and Maintenance

Permeable pavements require regular inspection and maintenance to ensure proper functioning. The limiting factor for permeable pavers is clogging within the aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. layers, filler, or underdrainA perforated pipe used to assist the draining of soils.. Ideally, signs should be posted on the site identifying permeable paver and porous pavement areas. This can also serve as a public awareness and education opportunity. See: Permeable paving: Maintenance

Life cycle costs

Initial construction costs for permeable pavements are typically higher than conventional asphaltA mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces. pavement surfaces, largely due to thicker aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. base needed for stormwater storage. However, the cost difference is reduced or eliminated when total life-cycle costs, or the total cost to construct and maintain the pavement over its lifespan, are considered. Other potential savings and benefits include reduced need for storm sewer pipes and other stormwater practices, less developable land consumed for stormwater treatment, and ancillary benefits (improved aesthetics and reduced urban heat island effect). These systems are especially cost effective in existing urban development where parking lot expansion is needed, but there is not sufficient space for other types of BMPs. They combine parking, stormwater infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface., retention, and detentionThe temporary storage of stormwater to control discharge rates, and allow for sedimentation. into one facility. See also: Cost analysis resources

Proprietary Links

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

Pre-cast with spaces

Pre-cast pervious

Cast in place

Plastic grid


  1. Bean, E.Z., Hunt, W, F., Bidelspach, D.A. 2007a. Evaluation of Four Permeable Pavement Sites in Eastern North Carolina for Runoff Reduction and Water Quality Impacts. Journal of Irrigation and Drainage Engineering. Vol. 133. No. 6. pp. 583-592.
  2. Legret, M and V. Colandani. 1999. Effects of a porous pavement structure with a reservoir structure on runoff water: water quality and fate of metals. Water Science and Technology. 39(2): 111-117
  3. Pratt, C.J., Mantle, J.D.G., Schofield, P.A. 1995. UK research into the performance of permeable pavement reservoir structures in controlling stormwater discharge quantity and quality. Water Science Technology. Vol. 32. No. 1. pp. 63-69.
  4. City of Portland. 2004. Portland Stormwater Management Manual. Prepared by the Bureau of Environmental Services (BES). Portland, OR.