How drainage works on concrete and rooftops

On slabs and roofs, water cannot percolate into soil. Your system needs a permeable turf backing over a drainage layer that creates open flow channels and moves water to existing scuppers, gutters, or floor drains.

  • Permeable turf backing that lets water pass through quickly.
  • Drainage pad or three dimensional panel to create air voids and flow channels.
  • Separation fabric where needed to protect membranes and keep fines out of the system.
  • Edge restraint that keeps the surface stable without blocking water paths.
  • Infill that supports blades without clogging drainage.

Required slope and water path

Verify slope to drains before you start. A functional slope is typically 1 to 2 percent toward scuppers or floor drains. Flat or back pitched zones need correction with crickets or tapered underlayment. Never obstruct scuppers, drain grates, or overflow paths.

  • Map all drains and overflows. Confirm the low points with a laser or level.
  • Ensure the drainage layer has continuous paths to each drain.
  • Keep seams and edges from forming dams. Leave clearances at drains per manufacturer guidance.

System build ups over concrete

Ground level slabs

  1. Clean the slab, repair birdbaths, and confirm slope.
  2. Install separation fabric if needed to control fines or alkalinity transfer.
  3. Lay a drainage pad or panel. Tape or clip per manufacturer guidance to maintain flow channels.
  4. Install permeable turf. Seam with turf approved adhesive and seaming tape.
  5. Add infill to spec, brush to settle, and verify water moves freely to the drains.
  6. Use a perimeter edge restraint or adhesive that does not block runoff.

Waterproofed rooftops

  1. Coordinate with the membrane manufacturer. Do not penetrate the waterproofing.
  2. Place a protection board or slip sheet specified for the membrane.
  3. Use a drainage panel with high open void and crush resistance. Maintain clear access to scuppers and drains.
  4. Install permeable turf with compatible adhesives. Weight the system with specified infill to address wind uplift.
  5. Confirm assembly fire rating and any ember or spread requirements per local code.

Typical thickness profile

  • Drainage pad or panel: about 0.25 to 1.0 inch.
  • Turf pile: about 1.0 to 2.0 inches depending on use.
  • Total build up: about 1.5 to 3.0 inches plus infill. Check door and threshold clearances.

Choosing the drainage layer

  • Drainage pads: Thin, flexible, and easy to roll out. Good for patios and small roofs with consistent slope.
  • Three dimensional panels or cups: High flow capacity and robust void space. Ideal where rapid drainage and airflow are priorities.
  • Shock pads with channels: Useful where fall protection or extra comfort is required. Verify permeability and channel continuity.

Match the layer to rainfall intensity, roof slope, and load limits. Keep continuous flow paths under seams and transitions.

Infill, cooling, and performance

  • Use clean, rounded infill that will not compact into a hard, non draining layer. Avoid dusty fines.
  • For rooftop heat, consider lighter colored or cooling infills and provide shade or rinsing as needed.
  • Select infill depth to meet performance needs such as play comfort and ball response while keeping permeability high.

Pet and odor management

  • Choose permeable turf and drainage layers that flush quickly.
  • Use antimicrobial or deodorizing infill for pet areas.
  • Rinse regularly and apply enzyme cleaners on a schedule tailored to usage.

Maintenance for reliable drainage

  • Keep scuppers, gutters, and floor drains clear.
  • Blow or vacuum debris so fines do not clog the surface.
  • Brush the turf and top off infill to maintain permeability.
  • Inspect seams and edges each season and after major storms.
  • For snow, use plastic shovels or a broom. Follow membrane guidance for deicers.

Common pitfalls to avoid

  • Using closed cell foam without flow channels.
  • Blocking scuppers or creating dams at seams and edges.
  • Ignoring slope or assuming the drainage layer fixes a back pitch.
  • Using incompatible adhesives on waterproofing membranes.
  • Skipping wind uplift and fire rating requirements on roofs.

Quick spec checklist

  • Permeable turf backing with high flow rate.
  • Drainage layer type, thickness, and compressive strength.
  • Slope verified at 1 to 2 percent to drains, with crickets as needed.
  • Infill type, color, and depth aligned to use case.
  • Edge restraint that allows runoff and resists uplift.
  • Assembly fire rating and roof wind considerations.
  • Total system weight per square foot and load limits.
  • Membrane protection and warranty coordination.

When to bring in a pro

Engage a qualified installer when you have waterproofing, high rise wind zones, code driven fire ratings, ADA transitions, or complex slopes. Getting the assembly right up front protects drainage performance and warranties.