How drainage works under synthetic turf

Artificial turf sheds water through the turf backing into a compacted aggregate base, then into soil, drains, or drainage panels. Water moves fastest when it can exit in a controlled direction and also infiltrate vertically through the base.

Surface flow vs. vertical infiltration

  • Surface flow: A slight grade moves water laterally toward a drain, swale, curb cut, pop-up emitter, or trench drain.
  • Vertical infiltration: Open-graded base stone and drainage panels store and convey water downward and laterally even when the surface looks level.

What actually controls performance

  • Base composition: Clean, open-graded aggregate drains faster than dense fines.
  • Compaction and thickness: Proper compaction avoids settling and preserves pore space for flow.
  • Defined outlet: Water needs a place to go. Plan the discharge point before grading.
  • Panels or pipes: Drainage panels and perforated pipe accelerate flow in tight soils or flat sites.

Grading targets by application

  • Lawns and play areas: Gentle crossfall to a defined outlet keeps surfaces usable quickly after rain.
  • Putting greens: Uniform, subtle grade preserves roll quality while moving water off the green.
  • Sports and training areas: Minimal cross slope for playability, with vertical drainage and subdrains doing heavy lifting.
  • Rooftops and balconies: Follow structural fall to roof drains or scuppers. Add drainage panels and a protection layer.
  • Pet runs: Prioritize rapid clearance to avoid puddles and odors. Panels plus a reliable outlet help in clay soils.

Conversions and quick math

  • Percent to inches per foot: 1% = 0.12 in per ft. 2% = 0.24 in per ft.
  • Inches per foot to percent: 1/8 in per ft ? 1%. 1/4 in per ft ? 2%.
  • Example: Over a 20 ft run, a 2% grade drops about 4.8 in.

Base build options that drain

Standard permeable base

  • Excavate to plan depth and shape the subgrade toward the outlet.
  • Install a geotextile separator to keep soil out of the base.
  • Place 3 to 6 in of open-graded stone (for example, No. 57) over subgrade.
  • Add a thin leveling course of angular screenings, then compact to spec.

Enhanced vertical systems for flat sites

  • Drainage panels under the turf create a high-void path for water across the entire field.
  • Perforated collector pipe at the low side moves water to the outlet when soils are tight.
  • Use clean stone above and below panels to maintain flow.

Outlet planning

  • Pick the discharge method early: pop-up emitter, daylight to grade, dry well, trench drain, or connection to an approved storm line.
  • Set the low point at the outlet. Grade all pathways so water cannot backtrack or pond against edging.
  • In expansive clays or high water table zones, prefer hard-piped outlets over infiltration alone.

Rainfall capacity considerations

Quality turf backings evacuate water quickly through perforations or fully permeable layers. The limiting factor is usually the base and soil, not the turf. Use open-graded stone for storage and rapid conveyance, add panels or pipe where soils infiltrate slowly, and verify that the outlet can handle local design storms.

Accessibility and playability notes

  • Accessible routes: Keep cross slope at or below 2% and running slope within ADA guidance for paths and entries.
  • Putting and sport surfaces: Keep grades consistent and smooth. Rely more on vertical drainage and subdrains to preserve performance.

Verification and QC

  • Set benchmarks and pull string lines to confirm grade before compaction.
  • Use a digital level or laser to check slope at multiple stations.
  • Flood test critical areas before turf goes down. Adjust base while it is still workable.

Common mistakes to avoid

  • No defined outlet: Water needs a destination. Plan it.
  • Impermeable base: Dense, fine-rich base layers can trap water. Use open-graded aggregate for faster flow.
  • High edging: Edging that sits above the turf traps water. Set edging to allow exit flow.
  • Ignoring roof fall: On rooftops, match the structural slope and keep pathing to drains clear.

When a flat look is the goal

If a level appearance is required, build a vertical drainage assembly: open-graded stone, drainage panels, and subdrains that tie into an outlet. The surface reads level while water moves below.

Specification checklist

  • Document slope, outlet type, base gradation, compaction, and drainage components.
  • Include acceptance criteria: slope tolerance, flood test outcome, and outlet flow path.
  • Match details to climate, soil, and use case. Overbuild drainage in tight soils or high rainfall regions.

Need backup on a tricky site

Send us your site plan and rainfall data. FusionTurf will help you tune the base, panels, and outlet so the install drains cleanly and stays playable.