What it is
Angular crushed stone sized roughly 3/4" to 1.5", sold by the ton. The dedicated drainage rock — sized and shaped to maximize void space for water flow while compacting enough to bear modest loads.
What it is for
Drainage applications, full stop:
- French drains. The rock that surrounds the perforated pipe in the trench. Water flows through the rock voids into the pipe.
- Downspout drain runs. Backfill around buried downspout extensions.
- Foundation perimeter drains. Around the foundation footing drain pipe.
- Retaining wall back-fill. Behind retaining walls to relieve hydrostatic pressure.
- Yard low-spot remediation. As fill in low spots that hold water.
Why lateral rock specifically vs other crushed stone
Three properties matter for drainage rock:
- Angular — locks together to support its own weight without collapsing.
- Uniformly sized — consistent voids for predictable water flow.
- Clean (no fines) — fines would migrate into and clog the void space.
Lateral rock is washed and screened to meet all three. Standard crushed limestone has too many fines for drainage applications — it compacts to a near-solid surface, which is great for driveways and terrible for drains.
How much do I need
| Application | Math |
|---|---|
| French drain (12" wide × 18" deep trench) | ~1 ton per 9 LF of trench |
| Downspout run (6" wide × 8" deep) | ~1 ton per 25 LF |
| Yard low-spot fill (6" deep) | ~1 ton per 25 sq ft |
| Retaining wall backfill (12" wide × 36" tall) | ~1 ton per 8 LF of wall |
The french-drain wizard computes drain rock plus pipe plus filter fabric for full installs.
Install (French drain reference)
- Trench at 1% slope toward outflow.
- Line trench with heavy woven fabric — full wrap top and bottom.
- 2 inches of lateral rock in the bottom.
- Set perforated pipe on rock, slots down.
- Fill rest of trench with lateral rock to within 4" of grade.
- Wrap fabric over the top — this is the seal.
- Backfill top with topsoil/sod or river rock for visible decorative drains.
Buying tips
- Lateral rock is heavier per cubic foot than decorative river rock. A ton fits in 18 cubic feet of trench rather than 22.
- Don't substitute pea gravel for French-drain fill. Pea gravel compacts and clogs.
- Always wrap with filter fabric. Without fabric, soil migrates into the rock and clogs the drain within 2-3 years.
Contractor notes
Bundle quotes for French-drain installs (rock + pipe + fabric).
In the field
