How drainage works under artificial grass on concrete
Quality artificial turf drains fast through perforations in the backing. The water still needs a path off or through the concrete. A slab with 1 to 2 percent fall toward an open edge or drain usually handles rainfall without help. A flat or cupped slab traps water and keeps the turf wet. That is when controlled relief like weep holes or drains help.
When weep holes make sense
- The slab has little or no slope and water ponds during a hose test.
- Edges are enclosed by curbs, walls, or raised borders that block runoff.
- The patio is covered, so evaporation is slow and puddles linger.
- You are adding a drainage mat and need outlets at the mat’s low edge.
When you can skip weep holes
- The slab already pitches 1 to 2 percent to a lawn, gravel band, channel drain, or scupper.
- There is a functioning perimeter drain you can use.
- Water leaves the surface within a few minutes in a hose test with no ponding.
Safer, smarter ways to move water
- Use existing edges: Leave a thin perimeter gap where allowed so water can exit to soil or gravel.
- Add a channel drain: Sawcut a slot and install a low-profile drain tied to storm or a French drain.
- Drainage mat: A permeable underlayment moves water sideways to an edge or drain. Pair it with outlets.
- Weep holes: Drill small, strategic holes only where water collects if other options are limited.
Weep hole planning guide
Size and depth
- Diameter: 3/8 to 1/2 inch is typical for relief holes in residential slabs. Larger is rarely needed.
- Depth: Through the slab into the compacted base or soil so water can drop below the concrete.
Location
- Place holes at the lowest points you confirmed with a level or hose test.
- Favor the down-slope edge or corners where water naturally collects.
- Avoid drilling near the home’s foundation unless you are routing water to a controlled drain path.
Spacing
- Along the low edge: start at 2 to 4 feet on center.
- Interior low spots: one hole in the center of the ponded area often solves it.
- Test after the first set. Add more only if water still lingers.
Safety checks before drilling
- Call 811 to locate utilities. Verify no electrical, gas, or plumbing lines under the area.
- Confirm the slab is not post-tensioned. If it is, do not drill without engineered direction.
- Keep holes away from structural footings and do not direct water toward the house.
Field test before you commit
- Clean the slab. Hose it down for 5 to 10 minutes.
- Mark any puddles that remain after 5 minutes with chalk.
- Use a 4-foot level or laser to confirm low points and flow direction.
- Plan holes or drains only where water stalls.
Installation best practices over concrete
- Prep the slab: Repair major spalls, vacuum dust, and clear debris from any weep holes or drains.
- Add drainage mat if needed: Use a permeable underlayment to move water sideways toward outlets.
- Dry-fit turf: Align seams away from the lowest flow paths if possible.
- Adhesive strategy: Glue at seams and perimeter. Avoid fully gluing the field so water can find paths to outlets. Keep adhesive off weep holes.
- Infill and brush: Use the specified infill and power broom to stand fibers and promote even drainage.
Climate and code considerations
- Cold climates: Ensure discharge does not freeze across walkways. Keep outlets clear.
- Soils: If subgrade is dense clay, prefer edge drains or a channel drain to avoid slow infiltration.
- Local rules: Do not discharge to a neighbor’s property or toward the foundation. Check local codes if tying into storm systems.
Quick decision checklist
- Water leaves the slab quickly in a hose test: no weep holes.
- Ponding persists and edges are trapped: add weep holes or a channel drain.
- Unsure about utilities or slab type: stop and bring in a qualified installer.
Need backup?
If the slab is tricky, a FusionTurf installer will map flow, pick the right outlets, and protect your warranty. Simple. Dry. Done right.
