Permeable Pavers: Base Layers, Stone Sizes, Upkeep
Permeable pavers are concrete pavers with wider joints filled with small clean stone instead of sand, laid over layers of open-graded crushed stone. Rainwater passes through the joints into the stone base, which stores it and lets it soak into the soil or drain out through a pipe. That reduces runoff, puddles, and the need for separate stormwater systems. The base is different from a standard paver base: it uses clean, washed stone with no fines, in specific sizes, and is often much deeper.
Volume and tonnage calculator →Typical layer system
| Layer | Common material | Typical depth |
|---|---|---|
| Joint fill | #8 or #9 clean stone | Fills joints |
| Bedding | #8 clean stone | About 1 1/2 to 2 in |
| Base | #57 clean stone | About 4 in |
| Subbase | #2 or #3 clean stone | 6 to 24 in or more |
| Fabric | Geotextile on soil, if specified | — |
Exact depths depend on soil, traffic, and how much water the system must store. Designs often follow industry guidelines and local stormwater rules. See number 57 stone and number 8 stone.
Why no sand
Sand and dense-graded base with fines would clog the pores and stop water from moving. Every layer is open-graded so water can pass and be stored in the voids. Clean stone typically has about 30 to 40 percent void space.
Soil and drainage
| Soil | Design |
|---|---|
| Sandy or well-drained | Full infiltration |
| Moderately draining | Partial infiltration with an underdrain |
| Clay or poorly draining | Underdrain pipe to an outlet |
The soil is usually not compacted heavily in infiltration designs, to keep it permeable, although the stone layers are compacted.
Edge restraints
Permeable systems need strong edges, often concrete curbs, because there is no fine material to lock the pavers. See paver edge restraint.
Maintenance
- Sweep debris and leaves regularly.
- Vacuum sweep the surface periodically to remove fines from joints.
- Replace joint stone as needed.
- Avoid storing mulch or soil on the surface.
Clogged joints reduce infiltration, but vacuuming usually restores it.
Cost and benefits
Permeable pavers cost more than standard pavers because of the deeper stone base. They may reduce or eliminate other stormwater costs and can count toward impervious area limits in some codes.
Alternatives
Pervious concrete and porous asphalt work on similar principles. See pervious concrete.
Estimating stone
For a 400-square-foot area with 2 inches of #8, 4 inches of #57, and 8 inches of #2, you need about 2.5, 4.9, and 9.9 cubic yards respectively, before compaction. Use the asphalt base calculator for tons.
Bottom line
Permeable pavers use open joints filled with small clean stone over layers of #8, #57, and #2 stone with no fines, letting water drain into the base. Match depth and underdrains to soil, use strong edges, and vacuum sweep periodically to keep joints open.
Questions people ask
What base is used for permeable pavers?
Layers of clean stone: #8 bedding, #57 base, and #2 or #3 subbase.
Can I use sand in permeable pavers?
No, sand clogs the joints and base.
Do permeable pavers work on clay soil?
Yes, with an underdrain to carry water away.
How do you clean permeable pavers?
Sweep regularly and vacuum sweep the joints periodically.
Related guides
- Number 57 Stone: Size, Weight, Uses, and Coverage
- #8 Stone: Size, Uses, and Weight per Yard
- Pervious Concrete: How It Drains and Where It Fits
- Paver Edge Restraint: Types and How to Install It
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