Pervious pavement allows stormwater to pass through the driving surface and into the aggregate reservoir below, where it infiltrates into the subgrade or is collected by an underdrain. It is one of the most effective stormwater BMPs available because it treats and infiltrates water right where it falls, eliminating the need for surface collection and conveyance to a separate treatment facility.

It is also one of the most maintenance-sensitive BMPs, and a pervious pavement installation that is not maintained will fail within a few years. This article covers the three main types, their performance characteristics, and the maintenance reality that every project owner needs to understand before committing to pervious pavement.

Three Types of Pervious Pavement

Pervious Concrete

Pervious concrete (also called porous concrete or permeable concrete) uses the same Portland cement binder as conventional concrete but with a gap-graded aggregate and little to no fine aggregate. The result is a concrete with 15 to 25 percent void space that allows water to pass through at rates of 3 to 8 inches per minute when new.

Appearance: Rough, open-textured surface with visible aggregate. It does not look like conventional concrete and cannot be broomed to a smooth finish. The surface has a "rice crispy" texture.

Strength: 2,000 to 4,000 psi compressive strength, lower than conventional concrete. Adequate for parking lot and pedestrian loads but not recommended for heavy truck traffic.

Installation: Placed and struck off with a vibrating screed, then compacted with a roller. The placement window is tight — pervious concrete sets quickly and cannot be reworked once it stiffens. Experienced crews are essential. Curing is critical and must begin immediately.

Porous Asphalt

Porous asphalt uses an open-graded aggregate mix with modified asphalt binder. The void content is typically 16 to 20 percent. Infiltration rates are comparable to pervious concrete when new.

Appearance: Similar to conventional asphalt but with a coarser, more open texture. The difference is less visually obvious than pervious concrete.

Strength: Comparable to conventional asphalt for parking lot loads. The structural capacity is primarily in the aggregate base below, not the surface course.

Installation: Mixed and placed at temperatures similar to conventional asphalt. The mix design is specific — standard hot-mix is not porous. The compaction is lighter than conventional asphalt to preserve the void structure.

Permeable Interlocking Concrete Pavers (PICP)

PICP systems use concrete pavers with joints or openings filled with small aggregate (typically ASTM No. 8 or No. 89 stone). Water enters through the joints and passes into the aggregate base below. The paver units themselves are impervious; the permeability is in the joints.

Appearance: Architectural — available in a wide range of colors, patterns, and textures. PICP looks like a premium hardscape material, which makes it acceptable for high-visibility areas where pervious concrete or porous asphalt would not be aesthetically appropriate.

Strength: Individual paver units have compressive strengths of 8,000+ psi. The system can handle heavy vehicle loads if the base is properly designed. PICP is used in ports, loading docks, and fire lanes.

Installation: Pavers are set on a bedding layer of small aggregate (not sand) over the open-graded aggregate base. The joints are filled with aggregate. The system is modular, so individual pavers can be removed and replaced for utility access.

The Aggregate Reservoir

All three types of pervious pavement sit on an aggregate reservoir — a layer of open-graded crushed stone (typically ASTM No. 57 or No. 2 stone) with approximately 40 percent void space. This reservoir serves two functions:

1. Storage: It temporarily stores the infiltrated stormwater until it can percolate into the subgrade. The storage volume is the reservoir thickness times the void ratio times the pavement area. A 12-inch reservoir with 40 percent voids provides 4.8 inches of storage per square foot of pavement.
2. Structural support: It distributes vehicle loads to the subgrade, similar to the aggregate base in a conventional pavement section.

If the native subgrade soil has an infiltration rate below 0.5 inches per hour (clay soils), an underdrain is installed at the bottom of the reservoir to prevent the system from saturating and failing. The underdrain collects the water and conveys it to the storm drain system. This is called a "partial infiltration" or "no infiltration" design, depending on whether any water infiltrates into the subgrade.

Maintenance Requirements

This is where pervious pavement projects succeed or fail. The surface voids clog over time with sediment, organic debris, and fine particles tracked in by vehicle tires. Once clogged, the pavement is impervious and provides no stormwater benefit.

Routine Maintenance

• Vacuum sweeping — the primary maintenance activity. A regenerative air sweeper or vacuum sweeper removes accumulated sediment from the surface voids. Frequency: quarterly at minimum, monthly in high-traffic or high-sediment areas. Standard rotary broom sweepers push debris into the voids and make clogging worse — they must not be used on pervious pavement.
• Pressure washing — for severely clogged areas. High-pressure water with vacuum recovery can restore infiltration capacity in localized clogged zones.
• Joint aggregate replacement (PICP only) — over time, some joint aggregate is lost to vacuum sweeping and traffic. The joints should be inspected annually and aggregate replenished as needed.

What Kills Pervious Pavement

• Construction traffic. Heavy trucks and equipment during construction track mud and debris into the pavement surface, clogging it before the project is even occupied. Pervious pavement should be the last thing installed on a construction site, or it should be covered and protected until construction is complete.
• Sanding and salting. In cold climates, sand applied for traction fills the voids instantly. Salt is less damaging but still contributes to clogging. This is a major limitation in northern states.
• Landscape mulch and soil. Adjacent landscaping that washes onto the pavement during rain events clogs the surface. Pervious pavement should be graded so that landscape areas drain away from it, not onto it.
• Lack of sweeping. If the property owner does not commit to the vacuum sweeping schedule, the pavement will clog within 2 to 5 years and lose its stormwater function.

Stormwater Credit

Most stormwater regulations allow pervious pavement to receive credit as an infiltration BMP, a treatment BMP, or both. In the Bay Area under C.3, pervious pavement can be used to meet the biotreatment or infiltration requirement for the area it covers. In Portland under BES, it can be used to meet the on-site stormwater management requirement.

The credit typically requires a maintenance agreement recorded against the property, specifying the vacuum sweeping frequency and requiring annual inspection reports. If the maintenance lapses, the stormwater credit can be revoked, which may trigger a violation of the project's stormwater permit.

Cost Comparison

Pavement Type	Installed Cost ($/SF)	Design Life	Maintenance Cost ($/SF/yr)
Conventional asphalt	$3-6	15-20 years	$0.10-0.25
Porous asphalt	$5-10	15-20 years	$0.50-1.00
Conventional concrete	$6-10	25-30 years	$0.05-0.15
Pervious concrete	$8-14	20-25 years	$0.50-1.50
PICP	$12-20	25-30+ years	$0.50-1.00

The premium for pervious pavement over conventional pavement is typically 40 to 100 percent in installed cost. However, if the pervious pavement eliminates the need for a separate bioretention basin or detention facility, the net project cost may be comparable or even lower. This trade-off analysis should be run during schematic design.