Why a sub-base matters on soil

Soil moves, holds water, and grows weeds. A properly built aggregate base creates a stable, free-draining platform that keeps the turf flat, clean, and consistent through weather and heavy use.

  • Stability: Prevents ruts, ripples, and seam stress.
  • Drainage: Moves water away quickly and reduces mud and odors.
  • Longevity: Protects backing and seams from ground movement.
  • Finish quality: Delivers a smooth, even grade for a clean look and safe footing.

Recommended base materials

Use these

  • 3/4 inch minus crushed stone or Class II road base with fines for compaction and interlock.
  • Decomposed granite or 1/2 inch minus crushed rock where available.
  • Optional leveling layer: 1/4 to 1/2 inch of stone dust or coarse sand over compacted base.

Avoid these

  • Pea gravel or round rock that will not lock in place.
  • Topsoil or organic mixes that hold water and decompose.
  • Excess loose sand as the only base, which can shift and rut.

Depth and drainage specs

  • Typical lawns: 3 to 4 inches of compacted aggregate.
  • Pets, play, heavy traffic, clay soils, or freeze thaw regions: 4 to 6 inches.
  • Drive lanes or high point loads: 6 inches or more, per site conditions.
  • Slope: 1 to 2 percent away from structures for surface drainage.
  • Compaction: Build in 2 inch lifts and compact to about 90 to 95 percent using a plate compactor.
  • Separation: Use a breathable geotextile fabric to separate soil from base where soil is soft or weedy. Do not use plastic sheeting.

Step by step: building the base on soil

  1. Plan grade and edges. Set a 1 to 2 percent slope and define a solid perimeter edge.
  2. Excavate. Remove sod, roots, and soft soils to the design depth plus turf thickness.
  3. Prep utilities. Cap irrigation and set sleeves if needed.
  4. Install geotextile (as needed). Lay a breathable fabric over soil to prevent mixing and reduce weeds.
  5. Place aggregate in lifts. Spread the base in 2 inch layers, lightly moisten, and compact each lift.
  6. Set final grade. Screed the surface true to line and slope, keeping the base firm and flat.
  7. Add a thin leveling course. Use 1/4 to 1/2 inch of stone dust or coarse sand and compact again.
  8. Quality check. Walk the surface. It should feel solid with no pumping or low spots.
  9. Install turf. Lay, seam, secure the perimeter, then add infill per product spec and brush.

Adjust for soil and climate

  • Heavy clay: Increase base depth, use geotextile, and consider a perforated drain or French drain at low points.
  • Sandy soils: Use a well graded crushed stone that compacts and interlocks.
  • Freeze thaw: Increase depth and use angular rock to reduce heave. Keep the grade consistent.
  • High rainfall: Favor open graded crushed rock and maintain the full 1 to 2 percent slope.

Common mistakes to avoid

  • Setting turf directly on soil.
  • Underbuilding the base depth for the site conditions.
  • Using round rock or loose sand that shifts under load.
  • Skipping geotextile on soft or weedy subgrades.
  • Ignoring slope near patios, pools, or foundations.

Simple quantity calculator

Volume needed equals area times depth in feet. One cubic yard equals 27 cubic feet.

  • Example: 100 square feet at 3 inches deep is about 25 cubic feet, which is roughly 1 cubic yard.
  • Buy a little extra to account for compaction and trimming.

When is a sub-base optional?

Over solid concrete or asphalt in good condition, you typically do not need a full aggregate base. Use a drainage mat or foam pad for comfort, plan water escape, level as needed, then install and infill the turf.

Finish the system right

  • Perimeter: Secure edges with bender board, concrete nailer strip, or pavers.
  • Infill: Install the specified infill for fiber support, cooling, and performance.
  • Maintenance: Keep debris off the surface and brush periodically to maintain fiber lift.

Spec snapshot

  • Material: 3/4 inch minus crushed stone or Class II road base.
  • Depth: 3 to 4 inches typical, 4 to 6 inches for heavy use or challenging soils.
  • Slope: 1 to 2 percent minimum away from structures.
  • Compaction: About 90 to 95 percent, compacted in 2 inch lifts.