Why your sub-base choice matters

The sub-base is the load-bearing, drainage layer under your turf. Get it right and your surface stays smooth, drains fast, and resists waves, rutting, and frost movement. The winning formula is angular rock with fines that locks up under compaction while still moving water.

Best sub-base options and specs

3/4 inch minus crushed stone

  • Makeup: Angular crushed rock up to 3/4 inch with fines for dense compaction.
  • Why it works: Interlocks for stability, fines fill voids, and the gradation keeps water moving.
  • Target compaction: 95 percent of maximum dry density (Standard Proctor) in thin lifts.

Class II road base

  • Makeup: Well-graded aggregate base course designed for pavements.
  • Why it works: Predictable gradation and performance across climates and load types.
  • Use cases: Residential lawns, pet yards, commercial landscapes, light recreational areas.

Decomposed granite (DG)

  • Makeup: Weathered granite with sand-sized particles and fines.
  • Why it works: Packs tight with a smooth finish and drains when properly graded.
  • Tip: Use a moist, well-graded DG and compact in thin lifts. Add a thin 1/4 inch minus screed layer for final grading if needed.

Regional material equivalents

  • California: Class II Aggregate Base
  • Arizona: ABC Aggregate Base Course
  • Virginia: 21A or 21B Crusher Run
  • Maryland and Mid-Atlantic: CR-6
  • Nevada: Type 2 Base
  • Texas: Flex Base (TxDOT Item 247)

If you are sourcing locally, ask for an angular, well-graded base with fines that can compact to 95 percent density.

How to build a turf base that lasts

  1. Excavate: Remove turf and soil to the planned base depth plus turf thickness. Strip all organics.
  2. Shape subgrade: Establish a 1 to 2 percent slope away from structures. Knock down high spots and fill low spots.
  3. Separate: Install a non-woven geotextile over clay or weak soils to prevent mixing and improve stability.
  4. Place base in lifts: Spread 2 inch lifts of 3/4 inch minus or Class II. Lightly moisten.
  5. Compact: Vibratory plate compact each lift to 95 percent density. Repeat to full depth.
  6. Fine grade: Screed a 1/2 inch or less leveling course using 1/4 inch minus or DG. Compact smooth.
  7. Edge restraint: Install bender board, concrete curb, or treated nailer to confine the base.

Base depth guidelines

  • Stable soils, light foot traffic: 3 to 4 inches of compacted base.
  • Clay soils, pets, or heavier use: 4 to 6 inches.
  • Play areas and sports use: 6 inches or more, plus any required shock pad per safety spec.
  • Freeze-thaw regions: Add 1 to 2 inches to the above depths and prioritize drainage.

Drainage, separation, and stability

  • Geotextile: Use non-woven fabric over clay and expansive soils. It stops fines from pumping into the base.
  • Slope: Maintain 1 to 2 percent surface fall. Flat yards still need micro-grade for runoff control.
  • Weed control: A pre-emergent under the base and a quality turf backing reduce growth pressure.
  • Perimeter: Confine the base so it cannot creep. Good edges keep seams tight and surfaces flat.

What to avoid

  • Pea gravel or round rock: Rolls under load and will not lock up.
  • Unwashed sand or loamy soil: Holds water and loses density.
  • Open-graded stone with no fines: Drains but does not compact into a stable platform.
  • Organic fill or topsoil: Decomposes and settles.
  • Poorly processed recycled concrete: May include wire or oversized chunks. Use only clean, well-graded recycled base when locally approved.

Ordering the right amount

Calculate loose material before compaction, then add waste and shrinkage.

  • Volume in cubic yards = Area (sq ft) x Depth (inches) / 324
  • Example: 600 sq ft at 4 inches = 600 x 4 / 324 ? 7.41 cubic yards
  • Add 10 to 15 percent for compaction and grading losses.

Quality checks

  • Proof roll: Walk or roll the base. No pumping, ruts, or soft spots.
  • Flatness: 10 foot straightedge with no more than 1/4 inch deviation for putting greens and tight installs.
  • Water test: Light hose-down. Water should infiltrate and move along the grade, not pond.

Regional and site considerations

  • Cold climates: Use angular aggregate, increase depth, and keep water moving away from the base.
  • High rainfall: Favor well-graded crushed stone and avoid fines-heavy mixes that stay saturated.
  • Expansive clay: Always use geotextile and consider thicker base.
  • Over concrete or asphalt: Add a drainage mat or panel underlayment to move water laterally.

Installer tips from the field

  • Compact in thin lifts and add just enough moisture to bind fines.
  • Use a 200 pound class vibratory plate or better for consistent density.
  • Pre-cut and dry-fit turf after base passes all checks. Do not hide base flaws under the turf.
  • Call 811 before you dig and follow local codes for drainage discharge.