Pervious pavement is designed to allow percolation
or infiltration of stormwater through the surface into
the soil below where the water is naturally filtered and
pollutants are removed. 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
Click here for additional detail
about the properties of impervious surfaces and their impact on water quality.
The 2005 MPCA Stormwater Manual offers a Fact Sheet
[ 387 KB pdf] about impervious surfaces that is also helpful and the Metropolitan Council
in the Twin Cities also has some good web information
[ 4 MB].
Pervious surface coverings if installed correctly and properly
maintained duplicate the structural and functional features
of traditional pavement.
|Local Examples of pervious pavement and pavers (images link to videos)
Diamond Vogel Paints
Scientific studies have linked high levels of impervious
surfaces to water quality degradation. Two thirds of the
impervious surfaces in developed communities are in the form
of pavement related to automobile usage. Any design that
uses alternatives to reduce impervious pavement is a positive
step towards improving the quality of a community's water
Pervious pavements are a recognized runoff reducing substitute
for normal pavements in development or redevelopment of:
The use of pervious pavement has been found to:
- Driveways, including residential driveways, low-traffic
roads, fire lanes and emergency access roads;
- Parking areas; especially over-flow parking and those
associated with office buildings, shopping centers and
recreational facilities ;
- Road shoulders and vehicle cross-overs on divided highways;
- Boat launching ramps;
- Others, including pool decks and patios.
- Reduce storm water runoff. (Even when pervious pavement
structure is saturated, its rough surface texture continues
to slow surface flow of stormwater);
- Replenish groundwater;
- Reduce flooding which may over-load combined sewer
sewage treatment plants;
- Require less land set aside and cost for development
of retention basins;
- Reduce pollutants in run-off;
- Reduce irrigation of area plantings based on the seepage
of rain into the sub soil surfaces;
- Reduce thermal
pollution (see also: temperature);
- Lessen evaporative
emissions from parked cars [ 85
- Reduce glare and automobile hydroplaning (skidding)
- Reduce pavement ice buildup.
In northern climates pervious pavement is easily compromised
by plowing that dislodges pavers and sanding which clogs
and disrupts the pavements filtration process.
Additional concern for heavy clay soils, often associated
with northern climates, can limit the usefulness of pervious
pavement. These soils are impervious and thwart expected
water quality improvements. The use of a graveled water
storage area built on top of clay soils is often not an
acceptable solution because storage capacity is quickly
overcome. Coupling drainage of graveled storage with additional
stormwater management practices is possible but the expense
of their design and development may be cost prohibitive.
Other issues that may be necessary to address include problems
for wheelchairs and other disabled individuals, effects
of parking lot sweepings, and resistance to damage from
snowplowing and de-icing operations. For more details see
Siting and Limitations information below.
St. Germain’s – Diamond-Vogel
was a % impervious surface limit on this lot because it
is within the Lake Superior coastal zone. See what they
Tejas Texas Grill & Saloon, the Hartley Nature Center,
and the University
Materials and Installation
There are various types of pervious pavement available
- Poured-in-place pervious
asphalt requires the same mixing and application
materials and the same ‘blacktop’appearance
of traditional impervious asphalt. The formula
is different with small stone and fine particulate
matter being removed and the quantity of tar reduced.
Sealants to waterproof new surfaces are not applied.
- Poured-in-place pervious
concrete surfaces like pervious asphalt
require similar machinery to standard concrete
pavement. Permeability is accomplished by using
larger pea gravel with lower water-to-cement ratio
creating a pebbly surface that is compacted with
- Block and concrete
modular pavers are designed to funnel water
between blocks into a basement layer of washed
sand and gravel where water slowly drains away
through the soil. The open areas in the paving
system provide 20-50% more opportunity for the
drainage of water than in the normal paved system.
Pavers are best used for driveways, parking areas,
shoulders along airstrips and highways, roadway
medians, boat launching ramps, emergency access
roads, fire lanes, sidewalks, grassed rooftops,
pool decks and patios.
- Grid pavers made
from either recycled plastic or concrete.
The grid pattern is usually honeycombed or lattice
shaped and the voids collect water during rain events,
which then slowly drains into the soil below.
- The grid pattern is filled with gravel and/or
grass to create a visually appealing appearance.
If grass is desirable, better growing conditions
are best encouraged by the addition of soil to
the subase sand and gravel mix.
- The grid's physical structure provides support
for vehicular use and helps prevent erosion.
- The flexibility of plastic type grid pavers
allows their use at sites with an uneven topography.
- Grid pavers are ideal for natural landscape
projects involving gardens or recreational areas
that support both vehicular and pedestrian traffic
and includes sidewalks, parking areas, golf cart
paths, residential driveways, fire lanes and
emergency access roads.
- Pervious pavement should be limited to low traffic
- Soil infiltration rate should be tested. A
minimum rate of 0.27 inches per hour is required
and a rate of 0.5 inches per hour is preferred.
- As a rule of thumb if septic tanks are used
in a region the soil will allow sufficient water
percolation for instillation of pervious pavement.
- Pervious pavements to be installed in low permeability
(clay) soils require the base materials to act
as temporary storage for storm events and subsequent
drainage through the soil. The base should be
composed of clean washed stone with 25-35%voids.
Capacity of the base material storage should
be incorporated into design criteria and related
to the desired performance of the system during
storm events. Typically design should accommodate
runoff for the 6 month-24 hour duration storm
- The system should fully drain after a storm
event within a minimum of 12 hours, and a maximum
of 72 hours (the recommended time is 24 hours).
- Pervious pavement sites should not be located:
- Within four feet above bedrock or a water
table's high point.
- Within 100 feet of a well.
- Within 10 feet of building foundation that
is above proposed pavement location or 100 feet
from a building foundation that is below the
proposed pavement location.
- Within close proximity of sources of contaminants
e.g. gas stations.
- On slopes that exceed five percent, the flatter
the surface the better.
- To ensure success it is critical to pay special
attention and follow engineering design for substrate
base and hydraulic design for entire project. Geotechnical
testing should be conducted prior project start,
to determine site conditions (see Siting above) and
derive engineering design plan.
- Excavation and grading need to accomplished with
light equipment to prevent soil compaction.
- Be sure to protect planned pavement area from storm
water runoff before and during construction by diverting
stormwater runoff. Stormwater events during construction
will contaminate cleaned and washed basement materials
by adding sediments that will fill the void spaces
designed to store water from storm events thereby
compromising desired pervious function of pavement.
If site stormwater protection is compromised all
base materials need to removed and again washed clean
- Basement layers and pavement can be laid, closely
following given engineering design criteria. A typical
cross section of layers involved in developing pervious
- Pavement –three quarters (asphalt) to
four inches thick (pavers)
- Filter Course - two inches thick made
of half-inch crushed stone
- Reservoir Course - thickness based on
runoff storage required and frost penetration,
made with one and a half to three inch diameter
- Filter fabric
- Existing soil managed to have minimal compaction
to retain soil porosity
- For information on plant selection and applications consult
E of the State of Minnesota Stormwater Manual-2005 [ 2.2
- Always check a municipalities building code to see
that pervious pavement is allowable. Environmental legislation
is creating a greater concern for water quality. Municipalities
are beginning to seek modifications to building codes
to encourage developing technologies that are environmentally
- Use of pervious pavements should be limited to low-traffic
areas. Only occasional truck traffic and no heavy semi
traffic should be allowed.
- Engineering requirements for pervious pavement are
similar to laying regular pavement and include:
- Pavement with sufficient thickness to protect subgrade
materials from being overstressed
- Use quality subgrade materials that can support
- Placement on a stable surface
- Compaction of materials to provide strength.
- Longevity of pervious pavement depends on a commitment
to following a rigid and detailed plan that starts with
site selection and carries through to a long term maintenance
program. The significant parts of a plan include:
- Continual inspection and enforcement of specifications
- Stringent control of sediment deposition on all
areas of pervious pavement, including:
- Pre-treatment of sediment laden runoff onto
pavement e.g. the use of a 25 foot wide
vegetative strip around areas of pervious pavement
subject to off-site drainage flows
- Scheduled vacuuming and jet washing of pavement
- Limited use of sanding materials and other
- Limiting heavy traffic use and excluding heavy
- Resurface areas where pavement has failed
- Cost of laying pervious pavement exceeds that
of traditional pavement, historically:
However higher instillation costs can be off-set by elimination
of the need for curbs, gutters, storm drains and large
retention ponds. Many communities will reduce stormwater
fees in recognition of these practices.
- Porous asphalt is 10-15% higher than regular asphalt
- Porous concrete is approximately 25% grater than
- Pavers can be as much as four times the expense
of either regular concrete or asphalt
- Correct site preparation may also increase these
costs. Costs that are site specific such as proximity
and cost of gravel supplies and site permeability
must be factored into estimates
- Prescribed maintenance costs for pervious pavement
amount to about $200 per acre per year (1999 dollars).
- The use of grid pavers filled with gravel or grass
may present a tripping problem with certain types of
footwear (high heels). The problem can be best addressed
by provision of small, narrow impervious walkways that
allow automobile access and loading.
- The use of pervious pavement may be coupled with other
stormwater management practices such as bioretention
and vegetative swales for optimum drainage results.
- Pervious pavement does function in the removal of pollutants.
Removal is accomplished through absorption, filtration
and microbiological degradation. Long term studies
show removal efficiencies of:
Practices that support continuing effective pollutant
- 82-95% of sediments
- 65% total Phosphorous
- 80-85% total Nitrogen
- high removal rates are also reported for Zinc,
Lead and Chemical Oxygen Demand (COD)
Pervious pavements have not been found to effectively
treat fuel leaks from automobiles.
- A strong maintenance program
- Extra treatment of site runoff (see # 7 above)
- Clean-washed sub-bedding materials (aggregate)
- Highly permeable soil
- Organic matter in sub-soil
- Sub-bedding zone that drains within 24 hours. If
soils are not able to dry out between rain events
anaerobic (without Oxygen) conditions may develop
and slow microbiological decomposition
- The sub-base or gravel layer becomes a water reservoir
in a pervious pavement system. The size of the reservoir
can be varied by design to better address local needs.
The addition of a perforated pipe, placed near the top
of the reservoir, to discharge excess water collected
in the reservoir, to adjacent stormwater management structures
facilitates storm water control.
- Additional forms of stormwater reservoirs can be added
to stone reservoirs below pavement surfaces. These should
be designed to accommodate stormwater runoff for the
local engineering design storm and allow infiltration
through sub-surface soils.
- Proper site selection and instillation is vital to
success. Many design engineers and contractors lack expertise
with pervious pavement technology. Selection of an instillation
team should be based on previous successful experiences.
- The ability to perform regular maintenance is important
to long term success and an expected useful life of 15-20
years. Maintenance contracts stipulating quarterly vacuuming
and/or power washing are recommended. If equipment and
resources are not available for maintenance, pervious
pavement is not recommended.
- Incorrect installation and inadequate maintenance are
the primary cause for the high rates of failure experienced
with pervious pavements. At Hartley Nature Center, when
they first installed Grass Pave 2 for additional parking
spaces they used Class 5 limestone gravel as an underlayment
and for covering the grid system. This was a mistake
because the limestone became fairly impermeable when
- Porous pavement should be used with caution in cold
climates. Regular winter pavement maintenance such as:
An additional concern is the permeability of clay soils
or basement rock beneath the pervious pavement. However,
this can be addressed to some extent by engineering design.
The sub-bedding or gravel placed below the pavement material
will function not only as a water reservoir during storms
but during winter will protect the surface pavement from
- Sanding compromises pervious pavement by clogging
pavement pours. Materials that collect in the snow
pack must be vacuumed after snow melt to prevent
clogging. The use of salt treatment is expensive
and will kill grass and adjacent plantings and also
not environmentally acceptable in many communities.
- Snow plowing can catch the edge of pavers and damage
the pavements surface.
- Areas adjacent to pervious pavement and subject to
erosion and sediment production require stabilization
to prevent clogging of pavement.
- There is a risk of contaminating groundwater and wells
if pervious pavement is located inappropriately close
e.g. siting should not occur any closer than 100 ft from
a well, or if its determined that installed pavement
is not sufficiently separated by the overburden and groundwater.
References: Guidebooks, websites and pamphlets
pdf file; it will be opened in a new window]
- Storm Water Technology Fact Sheet - Porous Pavement 1999
KB] Overview fact sheet that provides good
information on needed considerations, design criteria,
costs (dated), and contact information.
- Planning for Stormwater - Permeable Pavements
The NEMO (Nonpoint Education for Municipal Officials) website provides good overviews of materials used
in pervious pavements and how they fit into pervious landscape design.
Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring-Fact Sheet
Porous Pavements by US Department of Transportation-Federal
Highway Administration - an overview with good
illustrations referring to typical application and design
features of pervious pavements
Paver Research Summary
KB] Lake County Forest Preserve IL (2003).
A summary of investigations into use of pervious paver.
Includes a number of case studies, cost information and
an extensive reference section.
Building Sourcebook/Green Building Program-Pervious Paving Materials
Considerations for the use of pervious paving with information
rating practical commercial status and implementation
issues. Useful sections on use of grass in combination
with pavers, compared costs with traditional pavement
and a suppliers list.
Source Control Design Guidelines 2005; (pgs 12- 20)
MB] Greater Vancouver Regional District/
LANRC Consultants Ltd./ Kerr Wood Leidal Associates Ltd/
Goya Ngan - a useful, recent overview of pervious pavement
use and its design requirements.
- The State
of Minnesota Stormwater Manual (2005) is a valuable tool for stormwater
managers. The manual provides details on pervious
pavement [ 1.1
MB, Chap. 12-3] and other stormwater filtration
practices [ 1.2 MB, Chap. 12-6] applicable to Minnesota that help conserve, enhance, and
restores high-quality water in our lakes, rivers, streams, wetlands, and
- The Hillsdale
County, MI website has
a section that
explains in detail the properties of impervious surfaces
and their impact on water quality.