Last Updated on October 20, 2026 by Umar Farooq
A permeable paver base is four layers of clean, open-graded stone with the fine dust left out. The Concrete Masonry & Hardscapes Association (CMHA) guide specification describes 2 inches of No. 8 stone as bedding, over 4 inches of No. 57 stone as the base, over a No. 2 stone subbase whose depth depends on the site. The usual sand-and-road-base recipe is the wrong one here, because fines clog the gaps the water needs.
I read the CMHA permeable spec, then three installer and supplier guides (one from Western Interlock), to see where they agree. The layers match; the thicknesses, fabric and compaction advice do not. For the paver itself, see our permeable concrete pavers guide.
Four layers of washed stone, and not a grain of sand
The CMHA guide specification (PAV-GSP-016) puts the build in a single paragraph: a 2 inch (50 mm) bedding layer of ASTM No. 8 stone, an open-graded base "typically No. 57 stone, 4 in. or 100 mm thick," and a subbase of No. 2 stone, or No. 3 or 4 if No. 2 is unavailable. Joints and openings get No. 8 stone as well, or washed No. 89 or No. 9 where the joints are narrow.
| Layer | Stone | Thickness | Where sources differ |
|---|---|---|---|
| Joint fill | No. 8 (or 89 / 9 for narrow joints) | Full joint depth | None |
| Bedding | No. 8 | 2 in (CMHA) | Western Interlock screeds about 1 in of 1/4 in-10 stone |
| Base | No. 57 | 4 in (CMHA) | Western Interlock says 4 to 10 in. A vendor guide says 4 to 6 in for foot traffic and 6 to 12 in for driveways |
| Subbase | No. 2 | Set by design | Western Interlock says 6 to 12 in. Hunker says whole excavations can reach 20 in |
The CMHA numbers are typical values for a licensed designer to edit, not a shopping list. Size the subbase for your site: it stores water, so its depth depends on how much rain it must hold and how fast your soil drains. A percolation test answers the second part, and one guide I read calls for one.
Why "no fines" is the whole point
A normal paver base is dense-graded: stone mixed with fine particles so it packs solid and sheds water. A permeable base does the opposite on purpose. The CMHA spec requires all the stone to be washed, with less than 2 percent passing the No. 200 sieve. The gaps between the stones become storage space for water, and a few shovelfuls of dust can plug them.
That rules out the products you would normally buy for a patio. Skip the 3/4-minus, the crusher run and any "paver base" bag. Our paver base material guide explains how those dense mixes behave. Sand is out too: the vendor guide says outright not to use it as a base, and Western Interlock excludes bedding sand and road base. (A permeable system is the only paving job where the stone yard is allowed to be fussy about dust.)
Leave the soil underneath alone
This is where permeable builds differ most from habit. On a standard patio you compact the subgrade until it rings. On a permeable one, CMHA says compaction of the soil subgrade is optional and the project engineer decides. If it is compacted, the spec asks for at least 95 percent of standard Proctor density, and it warns that compaction reduces the permeability of the soil. Reduced infiltration may then call for a perforated underdrain.
My one strong opinion: the most common way to ruin a permeable base is to be thorough in the wrong place. A flawless, rock-hard subgrade under a drainage system is a very flat bathtub. Dig, check the bottom is clean and sloped (CMHA gives a typical minimum of 0.5 percent), and stop.
Geotextile is where the sources split. CMHA calls it a designer option, to be placed on the sides of the excavation and over the subgrade where used. Western Interlock lists it as step one, especially on soft or clay-heavy soil. The vendor guide recommends it for one build and warns against placing it above the base. If your soil is clay, read our landscape fabric for paver patio guide before you buy a roll.
Compact open stone in lifts, with a heavy plate
CMHA's compaction rules are specific:
- Spread the No. 2 subbase in lifts of no more than 8 inches. Make at least two passes in vibratory mode and two in static mode with a roller of at least 10 tons, until the stone stops moving.
- Spread the No. 57 base in one 4 inch lift and compact it the same way.
- Where a roller cannot reach, use a vibratory plate of at least 13,500 lbf with a compaction indicator, with at least two passes per lift.
- Do not crush the stone. Crushed stone makes fines, the thing you banned.
Compare that with ordinary base work. ICPI Tech Spec 2 assumes a 7,000 lbf plate for its 4 to 6 inch lifts and says thinner lifts suit plates around 5,000 lbf. The plate the CMHA permeable spec asks for is nearly twice the 7,000 lbf figure. I could not find a sourced weight for what a typical homeowner rental yard hands over, so check the rating on the plate in front of you. For a small patio, thinner lifts with the biggest plate you can rent beat one fat lift every time. See our how to compact gravel guide for the lift routine.
Screed the bedding, fill the joints, seat the pavers
Screed the No. 8 bedding to a consistent 2 inches, flat to within 3/8 inch over a 10 foot straightedge, and keep off it. Lay the pavers, fill the joints with No. 8 (or No. 89 or 9 for narrow joints), sweep the surface clean, then seat the pavers with a low-amplitude plate of at least 5,000 lbf, running at 75 to 90 Hz. At least two passes, then top up the joints and repeat.
Two edge rules matter. CMHA says not to compact within 6 feet of unrestrained edges, and not to use steel-spiked edging for vehicle traffic. Use precast concrete, cut stone or concrete. Chip-filled joints grip less than sand-filled ones, so the edge has to do more of the holding.
How much stone you will actually buy
Here is my own arithmetic, with an assumption in it. Take a 10 by 12 foot patio (120 square feet) with 2 inches of bedding, 4 inches of base and a 6 inch subbase, the low end of the sources above. That is 12 inches of stone, or 120 cubic feet, about 4.4 cubic yards. Using the Stone Center supplier figure of 1.35 to 1.7 tons per cubic yard, that is roughly 6 to 7.6 tons.
A standard patio on 4 inches of base and 1 inch of sand needs about 1.9 cubic yards, or 2.5 to 3.1 tons, so a permeable build uses about 2.4 times the stone. Our how much paver base do I need guide shows the sums. Check your own supplier's tons-per-yard figure before ordering.
Wash the stone, spare the soil, compact in lifts
Three habits decide whether the base drains: stone with no fines, soil left uncrushed, and compaction by lift with a plate big enough to do it. The pavers on top are the part people photograph, and the least of the three.
If you are standing at the stone yard wondering whether "clean" and "washed" mean the same thing, ask for the wash certificate. Dust is cheap. Digging it all out again is not.
FAQ
Can you use sand under permeable pavers?
No. Sand fills the voids and blocks drainage. The CMHA spec uses No. 8 stone as bedding, and the guides I read all exclude bedding sand.
Do permeable pavers need landscape fabric?
It depends on the source. CMHA calls geotextile a designer option, Western Interlock lists it first on soft or clay soil, and the vendor guide warns against putting fabric above the base. On clay, ask the designer.
How deep should a permeable paver base be?
CMHA's typical values are 2 inches of bedding and 4 inches of No. 57 base over a subbase sized for the site. Western Interlock gives 6 to 12 inches for the subbase. Add them up for your own excavation depth.
Can you use 3/4 minus under permeable pavers?
No. It contains fines, which fill the gaps and slow the water. Use washed, open-graded stone such as No. 57 and No. 2.
Do permeable pavers need an underdrain?
Only where the soil drains slowly or a liner is used. CMHA says that in low-infiltration soils, some or all drainage goes to perforated underdrains in the subbase.
