What Goes Under Artificial Grass? Layers and Drainage

A backyard lawn can look flawless on install day and still fail its first real storm. Water pools in the low spots, the blades mat down, and within a week the dog’s favourite corner starts to smell. In almost every case the turf itself is innocent. The failure hides in what goes under artificial grass, the stack of layers that has to carry every rainfall away from the surface.

We dissect that stack the way a factory sees it, from the turf backing at the top down to the graded soil at the bottom. Each layer gets its job, its typical thickness and the honest truth about whether you can skip it. What you will not find here is the roll-out-and-seam sequence, because that craft belongs to the installers and has its own walkthrough.

Why the Layers Under Turf Matter

The base is the one part of a lawn that nobody inspects at handover. Installers know this, and the weak ones quietly skip compaction or thin out the stone, because the mistake stays buried. You only meet the consequences months later, when the surface dips under the swing set and rainwater sits there for a day. By then the fix means lifting the whole lawn.

The failure chain is predictable. A soft or flat base lets water collect, standing water breeds mildew and odor, and saturated stone slowly shifts under foot traffic. Pet owners feel it first, because urine has nowhere to flush and the smell rises instead of draining away. A base built in the right order breaks that chain before it starts.

So treat this as the inspection sheet you wish you had on day one. We will tell you which layers are structural and which are optional, and we will name the one layer the pet industry loves to oversell. Where numbers matter, you get the figures installers actually build to.

What Goes Under Artificial Grass, Top to Bottom

Think of the build as a layer cake, where the bottom tiers decide whether the top holds its shape. What goes under artificial grass is a fixed sequence of jobs, not a pile of random material. Water enters at the surface, passes through the backing, and must keep moving down and across until it leaves the system. Every layer either helps that journey or gets in its way.

Only two layers are truly structural: the compacted stone and the slope beneath it. The leveling layer and the fabric are refinements, useful in some projects and wasteful in others. A full build-up typically claims around 6-6.5 inches of excavated depth once turf, stone and bedding are counted. Keep that figure in mind before you order stone, because depth is the one thing you cannot fake after the fact.

The Turf Backing: First Drainage Gate

Most landscape turf is manufactured with small holes punched through the backing, so rain drops straight into the stone below. Better specification grades go further with a fully permeable backing that drains across its whole area, not just at the punch points. The difference matters most on pet lawns and rooftops, where water volume per square meter is high. A backing that drains everywhere asks less of the layers underneath.

This is where the factory view earns its keep. We produce turf on PP+Net and PU backings, and the backing you choose changes how the base should be planned. A wider roll also means fewer seams sitting on the base. Our residential artificial grass range comes in 2, 4 and 5 metre widths by 25 metre rolls, covering roughly 50, 100 and 125 square metres per roll. Fewer seams mean fewer spots where the surface can bridge a dip in the leveling layer.

Weed Membrane: Above or Below the Base?

Ask three sources where the fabric goes and you may get three answers. One popular guide tells readers to roll a weed barrier under the base in step one, then places a geotextile above the stone in step three of the same article. Meanwhile, experienced installers argue that fabric buried under the base barely stops weeds and can trap bacteria in the moisture it holds. Both camps cannot be right, and the confusion costs buyers money.

Our position is blunt. Geotextile fabrics are separation layers, useful where fine soil would migrate up into clean stone. If you use one at all, it belongs between the sub-base and the leveling layer. For pet projects we tell buyers to skip it entirely, because a urine-soaked sheet buried under stone is a smell you fabricate yourself. Good compaction and a proper slope do more against weeds than any buried cloth.

The Sub-Base: Stone Choice and Thickness

This is the layer that answers the question for real. Ask any builder what goes under artificial grass on soil and the answer starts with crushed, angular stone, packed tight enough to walk on without a footprint. Manufacturers of professional installs call for Class II road base, spread 2-3 inches deep and compacted hard with a plate compactor. UK specifications reach for the same idea as Type 1 MOT. The general rule across guides is crushed stone at 2-4 inches, pushed up to 6 inches for play areas and other heavy use.

Stone selection follows one physics rule: angular pieces lock, round pieces roll. Guides converge on crushed stone 3/4 inch or smaller, and Northeast installers favour 3/8-inch angular bluestone, compacted to a 3-4 inch slab that sets almost like concrete. DIY builders who cannot source road base use decomposed granite at about 2 inches, then mist and roll a stabilizer into it so rain cannot wash the base away. Whichever stone you pick, the compaction passes and moisture control that follow are their own craft, and the full walkthrough lives in our artificial turf installation walkthrough.

Extra Drainage Layers for Wet Yards

Some sites defeat the standard stack before it is even built. Where the yard has a dip that always stays soggy, installers put a French drain in the low spot so water leaves the profile instead of pooling under the stone. Heavy clay soils and enclosed edges get a channel drain instead, a grated trench that catches surface runoff and pipes it to a safe outlet. Both sit below the stone, which is why they are decisions for the planning stage, not fixes for later.

Hard surfaces need the same thinking in reverse. Over concrete or rooftop decks, a drainage grid or air-gap mat lifts the turf off the waterproof surface so water can travel and the system can breathe. Installers commonly name products like AirDrain or DrainCore for this job. If your project lives in this corner of the map, tell us the surface and the water story, and we will help you match the stack before you order.

Grading the Soil Below Everything

The cheapest drainage layer costs nothing to buy, because it is the shape of the ground itself. Long before anyone asks what goes under artificial grass, the grade of the ground has already decided where rain will go. Guides agree that a slope of 1-2% works best, which installers translate into a drop of one to two inches per eight feet, always falling away from buildings. On clay or poorly draining ground that gentle fall is not optional, since the soil under the stone will not absorb water on its own. Installers check the fall with a level and string line while shaping, not after.

Preparation starts with stripping the ground clean. Guides call for removing about 2-4 inches of topsoil, along with every root, rock and old debris that could rot or heave later. The total excavated depth for a standard build lands near 6-6.5 inches once turf, bedding and stone are stacked in the plan. Measure the depth twice before ordering stone, because excavation is the one layer you cannot add back later. The exposed soil is then compacted, giving the stone a firm floor so the whole system cannot migrate downward.

Matching the Layers to Your Project

Standard stacks bend to real projects, and the adjustments are usually small once you know the rules. The table below collects the builds we are asked about most, from dog runs to drivable edges. For homeowners planning a full yard, the choices start with our residential-grade guidance and end with what your soil does in a storm. Turf itself runs $7-60 per square meter (indicative, request exact quote) by grade, while the stone beneath is priced by your local supplier.

One planning note ties the layers to the rolls themselves. Wide, few-seam layouts reward you only if the base is flat, so level the stone to the finished height before the turf arrives. Our rolls come in 2, 4 and 5 metre widths by 25 metres, and custom sizes can be made without internal seams for large or awkward footprints. The full installation walkthrough shows how those rolls meet the base on the day.

Frequently Asked Questions