Permeable Pavement

Information
Photo shows a driveway with small, interlocking brick blocks or pavers. The space is the width of two cars.
If your property has large paved areas, permeable pavement could be a good solution for managing runoff. Permeable pavement allows rain to soak into the ground. It is suitable for use with driveways, parking lots, and patios.
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What Is Permeable Pavement?

Permeable pavement is a hard surface that has enough gaps in it to allow rain to run through it. When rain runs through permeable pavement, it collects in a base layer of gravel, then gradually soaks into the ground. Permeable pavements are sturdy enough for vehicles and heavy pedestrian traffic.  

Permeable pavement is also called pervious pavement, porous pavement, pervious concrete, and porous asphalt. Below are descriptions of several choices of permeable pavement.

Photo shows a close up of pervious concrete, which has lots of tiny gaps between larger particles for water to flow through.
Example of pervious concrete

Porous Asphalt and Pervious Concrete

Porous asphalt and pervious concrete are like conventional asphalt and concrete but contain less fine aggregate content leaving open spaces for water to pass through and soak into the ground. Porous asphalt and pervious concrete are the most suitable for large areas including residential driveways and parking lots.


Photo shows close up of interlocking pavers
Example of permeable pavers

Permeable Paver Systems

Permeable paver systems have gaps between the pavers that allow water to pass. A layer of gravel under the paver system acts as a reservoir, holding rainwater while it soaks into the ground. Pervious paver systems are the most versatile type of permeable pavement and are suitable for residential driveways, patios, and parking lots.


Photo shows close up of concrete squares with plants growing in the centers
Example of turf block

Turf Block Systems

Turf block systems are pavers with empty spaces filled with soil and planted. Turf block systems are suitable for residential driveways. 


At a Glance: When to use which permeable paving solution

Property usesPorous asphaltPervious concretePermeable paversTurf block
Residential drivewaysYesNoYesYes
PatiosNoNoYesNo
Small parking lotsYesYesYesNo

How Permeable Pavement Works

Permeable pavement is an effective way to manage rain on your property without limiting use of space. Imagine eliminating the sheets of rain running across parking lots and driveways. Permeable pavement slows runoff and reduces the amount of rain that flows into pipes. This can reduce the risk of sewer backups and recharge groundwater.  

The gravel, known as subgrade, layered beneath the asphalt, concrete, or pavers also filters pollutants to help protect water quality both in our rivers and groundwater.  

Summary of Permeable Pavement Design Requirements

These site and design requirements can help you decide if permeable pavement might be appropriate for your project.

  • Permeable pavement is allowed on surfaces with slopes no greater than 5 percent.
  • Underlying soils should have a minimum infiltration rate of 2 inches per hour.
  • There are no setback requirements for permeable pavement.  
  • There must be 5 feet between the high groundwater level and the excavated bottom.   
  • The subgrade next to structures should slope away from the structures.
  • Use a minimum of 6 inches of washed, crushed 2- to ¾-inch or No. 57 rock under concrete or asphalt.
  • Consult the Stormwater Management Manual regarding required edge restraints.

For best results, keep in mind the following construction considerations:

  • Protect the subgrade from over-compaction during excavation.  
  • Do not excavate or compact the native subgrade in wet conditions.  
  • Consider the sequence of construction activities to protect the subgrade from traffic. Protect the paving from construction traffic and sediment after installation.   

When to Call a Professional

Call a professional designer if you have more vehicle traffic than a residential driveway.

Also, if your soil infiltration rate is less than 2 inches per hour, you will need to hire a designer to help you.  

Costs and Permits

Permeable pavement installation ranges in cost depending on the size and type of system.   

Pervious pavement systems used to replace public parking or walkway areas require a building permit from the Bureau of Development Services.

Commercial building permits are required for non-residential projects.  

Maintenance Requirements

Clean the surface once or twice per year to maintain permeable pavement.  

Permeable pavement is less prone to cracking or buckling from freezing and thawing. Studies indicate it requires less frequent repair and patching than conventional paving.  

Properly installed permeable pavement systems can last for more than 20 years.

Stormwater Management Manual

Consult the City’s Stormwater Management Manual for the complete set of requirements on how to safely site, build, and maintain pervious pavement or other stormwater management solution on your property.

Portland’s Clean River Rewards Program

Residential and commercial property owners who install qualified stormwater management solutions may be eligible for discounts on the stormwater charges of their sewer, stormwater, and water bill through Clean River Rewards.  

Permeable pavement that meets the safety and space requirements outlined in the stormwater management manual is eligible for Clean River Rewards for commercial, multi-family residential, and industrial accounts. Visit Clean River Rewards to learn more. 

Contact

Private Property Drainage Inquiries

phone number503-823-5858For questions from home and business owners about safe ways to manage the rain on their property or solutions to drainage problems.

Systems Development

Environmental Services
phone number503-823-7761Questions about sewer connections, stormwater management, and drainage reserves at the land use or building permit stage