Picture a heavy summer rain on a finished lawn. Water hits the blades, slips between the tufts, and looks gone. In reality a chain reaction has started. Surface to pile, pile to infill, infill to the small holes punched in the backing. Then through the open-graded stone base and into the native subgrade.
The chain runs in a fixed order, and each link has one job. We inspect these failures at the factory gate, on rolls that never made it out of the plant, and the same few causes keep turning up. We take the water path and the depth-and-slope decision together. Then the target slope and cold-climate fixes, perforation specs, and the four triggers that justify an underdrain. Edges, hardscape transitions, a table across five install surfaces, a diagnosis table, and a site check round it out.
How Water Actually Moves Through Artificial Grass
Artificial grass drainage does not work by absorption. The surface lets water pass through, like a sieve stretched over a sponge. The pile lifts water off the surface so it can move sideways and downward. The infill keeps the blades upright and guides droplets toward the backing. The backing carries the perforations or open weave that finally hands the water to the base.
The base is where most failures start. Treat the grass as a sieve and the base as a holding tank and a pipe at once. The stone holds a brief flood while the soil absorbs it, and the slope inside the stone carries the surplus to an edge or a drain. When any of those jobs slips, ponding appears within minutes of a storm.
On any artificial turf installation, four layers can be the bottleneck. Infill can clog with fines and seal the surface. Backing perforations can be partly blocked by glue during install. The open-graded stone can be choked by silt washing in from above or below. The native subgrade can be slow to absorb.
Deciding Depth and Slope Together
Structural layers, stone choice and the layer-by-layer order are covered in our guide to what goes under artificial grass.
Both variables can fail alone and still ruin a lawn. A deep base on a reversed slope holds water until the subgrade slowly drinks it, and the lawn smells sour. A correct slope on a thin base overflows in the first heavy storm.
Four-quadrant depth-and-slope decision:
1. Permeable soil with usable slope: thinnest base works; the slope does most of the work.
2. Permeable soil with no usable slope: deepen the base so it can buffer a storm surge.
3. Clay-heavy soil with usable slope: deepen the base and add a geotextile separator to keep fines out of the stone.
4. Clay-heavy soil with no usable slope: deepening alone is not enough; jump to the underdrain triggers in the next chapter.
Residential base depth, heavy-use thickness and the binding layer choice sit inside the essential layers under artificial turf guide. A typical home lawn runs about 75 to 100 millimetres of compacted aggregate; a pet yard or play zone goes thicker on an artificial turf installation.
The order of decisions matters more than the numbers. Pick the slope direction first, then choose the depth. Reversing the order usually puts money into the wrong layer and leaves the real failure untouched.
Slope, Fall and Cold-Climate Drainage
The step-by-step grading actions during install prep are covered in our artificial grass installation preparation walkthrough. The 1-2% target and dig-depth context sit in the layering guide linked above. What follows is the slope spec in numbers, the direction rules, and the cold-climate fixes that most pages skip.
Across the sources we trust, the target for the finished surface is a 1-2% fall running away from any structure and toward a clear outfall. That is about 10-20 millimetres of drop per linear metre. A small well-draining patio can drop to about 0.5% when both soil and base drain freely. Flat is never acceptable.
Engineers often write the same gradient as a ratio: 1:100 for a garden or balcony, and 1:100 to 1:80 on a rooftop. Direction matters as much as the percentage. Three rules