Pervious Concrete: The Concrete That Drains

What Makes Pervious Concrete Different

Regular concrete is designed to be dense and impermeable. Pervious concrete is the opposite—it's engineered with gaps.

The mix contains little to no fine aggregate (sand). Instead, it's mostly coarse aggregate (gravel) bound together with cement paste. The result looks like Rice Krispies treats: stones stuck together with gaps between them. Those gaps create a network of pores that let water flow straight through.

When rain hits a pervious concrete parking lot, it doesn't sheet off into storm drains. It drops through the concrete, into a gravel base below, and percolates into the ground. Zero runoff.

How It Works

The system has three layers:

1. Pervious Concrete Surface (4-8 inches)

The top layer you walk and drive on. Typical void content is 15-25%—enough to drain water fast while maintaining structural integrity. Higher void content means faster drainage but lower strength.

2. Aggregate Base (6-12 inches)

Clean, open-graded gravel (no fines) sits below the concrete. This layer stores water temporarily and lets it percolate into the soil. The base acts as a reservoir during heavy rain.

3. Subgrade (Native Soil)

Water eventually reaches the native soil and recharges groundwater. Soil percolation rate matters—sandy soils drain fast, clay soils don't. Sites with poor-draining soil may need underdrains.

Where Pervious Concrete Works Best

• Parking lots: The #1 application. Eliminates need for retention ponds in many cases.
• Driveways: Especially in areas with stormwater regulations or drainage problems.
• Sidewalks and pathways: Low-traffic areas are ideal.
• Pool decks: Water drains instead of puddling—no slipping.
• Patios: No more puddles after rain.
• Tree surrounds: Lets water and air reach tree roots in urban settings.

Where It Doesn't Work

• High-speed roads: Not strong enough for highway traffic.
• Heavy industrial: Can't handle constant heavy truck traffic.
• Freeze-thaw climates (sometimes): Requires careful design and maintenance in cold regions.
• High-sediment areas: Dirt and debris clog the pores over time.
• Slopes over 5%: Water runs off before it can infiltrate.

Cost Breakdown

Item	Pervious	Conventional
Material cost	$215-260/yard	$180-230/yard
Installed cost	$8-16/sq ft	$6-12/sq ft
Aggregate base	6-12" required	4" typical
Stormwater infrastructure	Often eliminated	Required

The higher upfront cost is often offset by eliminating retention ponds, storm drains, and other stormwater infrastructure. On a large commercial project, pervious concrete can actually cost less overall when you factor in the site work savings.

Strength and Durability

Pervious concrete is weaker than conventional concrete—there's no way around it. Those voids that let water through also reduce structural capacity.

• Typical strength: 2,500-4,000 PSI (vs 4,000-5,000+ for conventional)
• Traffic rating: Light to medium vehicle traffic. Passenger cars and light trucks are fine. Heavy trucks will damage it over time.
• Lifespan: 20-30 years with proper maintenance

The strength trade-off is acceptable for parking lots and driveways, but pervious concrete isn't suitable for structural applications or heavy-duty industrial use.

Installation Differences

Pervious concrete requires specialized installation. You can't pour it like regular concrete.

Key Differences:

• No slump: Pervious concrete has zero slump—it's stiff and crumbly, not flowable.
• No vibration: Vibrating would close the voids. It's placed and compacted with rollers or hand tools.
• Tight timing: The mix sets fast. Crews have 60-90 minutes max from mixing to final placement.
• Curing is critical: Pervious concrete must be covered with plastic within 20 minutes of placement and kept moist for 7+ days. Drying too fast destroys it.
• No finishing: You don't trowel pervious concrete. The rough, open surface is the final product.

Maintenance Requirements

Pervious concrete needs regular maintenance or it stops working. The pores clog with sediment, leaves, and debris over time.

Required Maintenance:

• Vacuum sweeping: 2-4 times per year with a regenerative air vacuum or commercial vacuum truck
• Pressure washing: Annual or semi-annual, perpendicular to the surface
• Keep it clean: Don't let sediment, mulch, or grass clippings accumulate
• Avoid sealing: Never seal pervious concrete—you'll block the pores
• Snow removal: Use plows carefully (blade up slightly). Avoid sand—it clogs pores. Salt is okay.

Skip maintenance and infiltration rates can drop 50-90% within a few years. A well-maintained pervious lot can function for decades.

Environmental Benefits

Pervious concrete is primarily an environmental technology:

• Reduces runoff: Can eliminate 70-100% of stormwater runoff
• Recharges groundwater: Water goes into the ground instead of storm drains
• Filters pollutants: Oil, grease, and heavy metals are captured in the aggregate base
• Reduces heat island effect: Lighter color and evaporative cooling lower surface temperatures
• Protects waterways: Less runoff means less pollution reaching streams and rivers
• LEED credits: Can contribute to sustainable site credits in green building certification

How Long Does Pervious Concrete Last?

With proper maintenance, 20-30 years. Without maintenance, infiltration capacity degrades significantly within 5-10 years, though the concrete itself remains intact. Regular vacuum sweeping is the key to longevity.

Can Pervious Concrete Handle Freeze-Thaw?

Yes, but it requires careful design. The open void structure actually helps—water drains through rather than saturating the concrete. Air-entrained mixes and proper drainage prevent freeze-thaw damage. Many pervious installations perform well in northern climates.

Is Pervious Concrete Strong Enough for Driveways?

Yes, for passenger vehicles and light trucks. A properly designed pervious driveway (5-6 inches thick over adequate base) handles normal residential traffic without issues. It's not suitable for heavy equipment or commercial truck traffic.

Can You Repair Pervious Concrete?

Small areas can be patched with pervious mix, but repairs are tricky. The new material must bond to old while maintaining void connectivity. Major damage usually requires panel replacement. Prevention (avoiding heavy loads, maintaining drainage) is better than repair.

Does Pervious Concrete Get Slippery?

No—the opposite. The rough, textured surface provides excellent traction even when wet. Water drains through instead of pooling on top, eliminating hydroplaning risk. Pervious concrete is actually safer than smooth conventional concrete in wet conditions.

Key Takeaways

• Pervious concrete has 15-25% void space for water drainage
• Drains water at 3-8 gallons per minute per square foot
• Costs $8-16/sq ft installed—more than conventional but may save on stormwater infrastructure
• Best for parking lots, driveways, sidewalks, and patios
• Not suitable for heavy traffic, steep slopes, or high-sediment areas
• Requires specialized installation—no slump, no vibration, immediate curing
• Maintenance is mandatory: vacuum sweep 2-4x/year to prevent clogging
• Lifespan of 20-30 years with proper care