Pervious Concrete: How It Drains and Where It Fits

Pervious concrete is a special concrete made with coarse aggregate and little or no sand, which leaves connected voids that let water pass straight through. Rain soaks into a stone reservoir base below instead of running off. It is used for parking lots, driveways, walkways, and patios where stormwater management matters. Pervious concrete requires careful mix design, installation, and maintenance to work well.

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How it works

Open-graded mix: cement paste coats coarse stone, often around 3/8 inch, leaving voids that can be 15 to 25 percent or more of the volume.
Stone reservoir base: clean, open-graded stone below stores water while it soaks into the soil.
Infiltration: water drains through the slab quickly, often at high rates when new.

Typical uses

Parking lots to reduce runoff and detention pond needs.
Driveways in areas with stormwater rules or limited drainage.
Sidewalks and patios.
Around trees, allowing air and water to reach roots.

It is generally not used for heavy truck traffic or high-speed roads.

Base and soils

Layer	Common materials
Pervious concrete slab	Often around 4 to 8 inches thick
Choker or filter layer	Smaller clean stone, sometimes #8
Reservoir base	Clean stone such as #57 or larger, depth sized for storage
Subgrade	Native soil, sometimes not compacted heavily to preserve infiltration

Soils with poor drainage may need underdrains. Engineers size the base for local rainfall. See #8 stone.

Pros and cons

Pros: reduces runoff, helps meet stormwater rules, reduces puddles and ice in some cases, and can recharge groundwater.

Cons: requires specialized installers, lower strength than conventional concrete, can clog if not maintained, and may be vulnerable to raveling or freeze-thaw damage if poorly installed.

Maintenance

Vacuum sweep periodically to remove sediment.
Keep soil and mulch from washing onto the surface.
Avoid sand for winter traction, since it clogs voids.
Avoid sealers that close voids.
Plow carefully with raised blades.

Pervious concrete vs other permeable options

Option	Notes
Pervious concrete	Continuous surface; specialized installation
Porous asphalt	Similar concept with asphalt binder; see porous asphalt
Permeable pavers	Joints filled with stone; easier repair
Gravel	Lowest cost; dust and migration

See permeable driveway for more options.

Cost considerations

Pervious concrete usually costs more per square foot than a standard slab once the deeper stone reservoir, specialized installation crew, and testing are included. Some of that cost can be offset on commercial sites when it reduces or eliminates detention ponds, storm sewer pipe, or stormwater fees. For a homeowner, the main reasons to choose it are local runoff rules, persistent puddling, or a desire to manage rain on site.

Ask installers whether they hold pervious concrete certification and for references on projects that are several years old, since long-term drainage is the real test.

Bottom line

Pervious concrete drains rainwater through open voids into a stone reservoir, reducing runoff for parking areas, driveways, and walks. It needs proper base design, skilled installation, and regular vacuum sweeping. Compare it with porous asphalt and permeable pavers before choosing.

Questions people ask

What is pervious concrete?

Concrete made with little or no sand, leaving voids that let water drain through.

Is pervious concrete strong enough for driveways?

It is used for driveways and parking, but not typically for heavy truck traffic.

Does pervious concrete clog?

It can clog with sediment. Regular vacuum sweeping helps maintain drainage.

Can you use sand on pervious concrete in winter?

Avoid sand, which clogs voids. Follow installer guidance on deicers.

What base goes under pervious concrete?

Clean, open-graded stone that stores water while it infiltrates.

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