Can you lay artificial turf over a concrete patio?

Keep the slab, or take it out

Turf can go straight over a concrete patio. Whether it should depends on what the slab does with water, because the turf won’t change that.

Keep the slab if:

• It falls away from the house, by at least a quarter inch per foot near the wall.
• Water runs off it after rain, with no puddles left behind.
• The surface is flat and whole, with no heaved sections or lips at the cracks.
• Water has somewhere to go once it leaves the low edge.

If any of those fail, take the slab out and build a drainable base. The rest of this article shows how to check each one.

Rain goes through the turf, then across the concrete

Outdoor turf is made to let water through its backing. New Jersey’s environment department says the backing needs “sufficient openings to let water drain through to the soil or storage area below” (NJ DEP, October 2025).

Over a stone base, that water soaks down. Over a patio, the layer below is concrete. The water can’t go down, so it spreads along the top of the slab until it finds an edge.

The industry has written about this for sports fields built on asphalt. The Synthetic Turf Council’s guidelines, revised in November 2011, say a field on conventional asphalt needs a slope, either a crown or a cross slope. They say to consider a drainage mat or a cushioning pad between the turf backing and the pavement, with drains at intervals, so water can move sideways under the surface. Without those, the guidelines warn, the infill “will become saturated during periods of heavy rainfall,” and it can travel with the water.

A patio isn’t a playing field. Water still behaves the same way on it. So the question for any turf on a slab is simple: how does water get from under the turf to the edge?

Check the slope first

The model residential code sets a number for hard surfaces beside a house. Section R401.3 of the 2021 International Residential Code requires impervious surfaces within 10 feet of the foundation to slope at least 2 percent away from the building (IRC R401.3).

Two percent is about a quarter inch of drop per foot. Across 10 feet, that’s roughly 2.4 inches.

The same section sends surface water to a storm sewer or another “approved point of collection that does not create a hazard.” So the fall is only half the job. The water also needs a safe place to end up.

An older patio may have lost that fall, or never had it. If yours now tilts toward the wall, turf won’t fix it. Water will still run to the house, only now it runs under a layer you can’t see. Which code edition applies depends on your town, so ask your building department.

Give the water a way off the slab

Once water is moving across the concrete, the low edge decides whether it leaves.

• Keep the low edge open. A border fastened tight along the downhill side can dam water under the turf. Ask how the edges are held down, and how water crosses the low one.
• Know where it goes next. A lawn, a gravel strip or a drain can take it. EPA says to make sure the ground slopes away from the foundation “so that water does not enter or collect around the foundation” (EPA).
• Pick infill that stays put. On a slab, water flows sideways under the turf instead of down into stone. New Jersey’s report warns that small rubber pellets are buoyant and may wash away. It names heavier infill, such as coated sand, as less likely to wash out.

A pad has to pass water too. The Synthetic Turf Council’s guidelines say that unless a pad is permeable by design, perforations should go through all of its cushioning layers.

How turf on a slab dries

Over soil, water that gets through the turf drains down and away. Over concrete, it can only run to an edge or evaporate. That leaves a thin, dark layer between the backing and the slab. How long it stays wet depends on the slope, the open edge and whatever sits in between.

Mold needs that moisture. EPA’s guide to mold puts it in one line: “The key to mold control is moisture control.” It also says wet materials dried within 24 to 48 hours will, in most cases, not grow mold.

EPA wrote that guide for inside a home, not a patio. The point still carries outdoors. A slab with a good fall, an open low edge and a path for water under the turf dries after rain. A flat or back-sloped slab keeps water sitting under it.

Watch the wall and the door

Many patios meet the house. Turf and infill on top of the slab raise the surface beside the wall.

The code sets a gap for wood there. Under Section R317.1 of the 2021 IRC, wood siding, sheathing and wall framing closer than 2 inches, measured vertically, to “concrete steps, porch slabs, patio slabs and similar horizontal surfaces exposed to the weather” must be naturally durable or preservative-treated wood (IRC R317.1).

That text doesn’t mention turf. It doesn’t say whether you measure from the concrete or from the top of the turf, so ask your building department. The simpler plan is to keep at least 2 inches below the siding measured from the finished turf. Our article on how close turf can go to your house covers the ground past the patio’s edge.

When removing the slab is the better call

Some patios make a fine base. Others don’t. Take the slab out if:

• It slopes toward the house and the fall can’t be corrected.
• Water sits on it after rain.
• It has heaved or cracked into uneven sections. The Synthetic Turf Council’s guidelines note that irregularities in the base “are typically reflected in the finished field surface.” A lip in the concrete becomes a ridge in the turf, and on a putting green, a ridge changes the roll.
• There’s no outlet at the low edge.
• The finished turf would sit less than 2 inches below wood siding.

With the slab gone, the turf can sit on the usual layers: prepared soil, a compacted stone base, and a backing that drains into it. Our guide to what goes under artificial turf walks through them.

Before you cover a patio with turf

1. Measure the fall. Set a level on a straight board and check the drop away from the house. Look for at least a quarter inch per foot within 10 feet of the wall.
2. Run a hose on it. Watch where the water goes and where it sits.
3. Walk the cracks. Note any lips, heaved sections or low spots.
4. Find the low edge, and decide where the water goes after it leaves.
5. Ask how water moves under the turf: a drainage mat, a perforated pad or neither, and which infill.
6. Measure the gap to wood siding, and keep 2 inches above the finished turf.
7. Ask your planning or stormwater office whether turf on the slab changes anything for your lot.

On the free visit we measure the patio and check the ground around it, including which way the slab falls. Then we draw a custom layout for you to approve, whether the turf goes over the concrete or on a new base. Call 303-349-2368.