Understanding Permeable Paver Systems

Understanding Permeable Paver Systems

What is Permeable Interlocking Concrete Pavement (PICP)?
PICP is a stormwater management solution that allows rainwater to filter through the joints between pavers, down through engineered aggregate layers, and into the soil below — reducing runoff, flooding, and pollution.

How the System Works

PICP is not just a surface material — it's a layered drainage system. From top to bottom:

  • Pavers – Solid concrete units (3⅛"/80mm thick) with open joints filled with No. 8, 89, or 9 stone aggregate
  • Bedding Layer – 2" ASTM No. 8 stone beneath the pavers
  • Base Layer – Min. 4" ASTM No. 57 stone for structural support
  • Subbase Layer – Min. 6" ASTM No. 2 stone for water storage and drainage
  • Geotextile Filtration Fabric – Placed on the bottom and sides of the open-graded base (when required by a design engineer) to prevent soil migration
  • Subgrade – Prepared native soil; depth and conditions determined by geotechnical analysis

Pedestrian-only applications may simplify to a single 6" ASTM No. 57 base layer.

Manufacturing Standards

Permeable concrete pavers are manufactured to meet:

  • ASTM C936 – Solid Concrete Interlocking Paving Units
  • ASTM C1782 – Segmental Concrete Paving Slabs
  • CSA A231.1/A231.2 – Canadian standard for precast concrete pavers and slabs

Key Uses & Applications

  • Driveways, parking lots, plazas, and pedestrian walkways
  • Low Impact Development (LID) stormwater strategies
  • Areas subject to local stormwater regulations or impervious surface limits
  • Sites needing reduced heat island effect or improved groundwater recharge

Important Design Considerations

  1. Subbase depth must be determined by site-specific hydraulic and structural engineering — not a one-size-fits-all spec.
  2. Traffic loading affects paver dimensions and aspect ratios — consult a structural engineer for vehicular applications.
  3. Geotechnical input is required to balance structural stability with soil infiltration rates.
  4. Geotextile selection must be verified against clogging resistance and must meet AASHTO M-288 requirements.
  5. Stone substitution – ASTM No. 2 stone in the subbase may be substituted with No. 3 or No. 4 stone where appropriate.

Maintenance & Long-Term Performance

All permeable pavements collect sediment over time, gradually reducing infiltration rate. This is expected and manageable:

  • Sediment accumulates near the surface where it's easiest to remove
  • Routine vacuum street sweeping is the primary maintenance method
  • Surface infiltration testing should confirm rates exceed 100 in/hr after any major maintenance or restoration
  • A site-specific Operations & Maintenance (O&M) Manual is recommended for commercial and municipal installations

Construction Site Protection Tips

Protecting a newly installed PICP system during ongoing construction is critical:

  • Schedule PICP installation strategically — early installation allows it to serve as a sediment trap, with joint material replaced at project completion
  • Avoid washout and debris from concrete, masonry, and drywall trades directly on the paver surface
  • A sacrificial asphalt layer over the base aggregate can protect the system during heavy construction traffic, but must be removed and the base re-graded before final paver installation
  • Plywood, tarps, and fabric covers have generally proven costly and ineffective as surface protection

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