The slope your patio needs is one-eighth inch per foot of distance

A patio should slope away from your house at a rate of 1/8 inch of drop for every 12 inches of horizontal distance. This means a 12-foot-wide patio would drop 1.5 inches from the house to the far edge. This slope is steep enough to move water away reliably but shallow enough that you won't notice it when you walk across the surface or set down a chair.

The slope matters because standing water on a patio breaks down the surface, rots wood nearby, and creates a slipping hazard. Without slope, water pools in low spots and sits there for days after rain. With the correct slope, water runs off in minutes and drains into the surrounding soil or a drainage system you've installed.

The 1/8 inch per foot rule applies whether you're building with concrete, pavers, stone, or composite decking. It's the standard used by builders and landscape contractors because it balances drainage performance with comfort underfoot.

Key Takeaways

  • Slope your patio at 1/8 inch per foot away from the house to prevent water from pooling and damaging the surface.
  • A 12-foot patio should drop 1.5 inches total; a 20-foot patio should drop 2.5 inches.
  • Measure slope during construction by using a level and a tape measure, or by calculating rise over run before you pour or lay materials.
  • Slopes steeper than 1/4 inch per foot feel noticeably tilted when you walk on them and can cause furniture to slide.
  • If your patio is already built and water pools in spots, you may need to add a French drain or regrade the surrounding soil.

How to calculate the slope for your patio size

The math is straightforward: multiply the distance from your house by 1/8 inch. A 10-foot patio needs a 1.25-inch drop. A 16-foot patio needs a 2-inch drop. A 20-foot patio needs a 2.5-inch drop.

Write down the total drop you need before you start building. If you're pouring concrete, this number tells you how much lower the far edge of the forms should sit than the edge closest to the house. If you're laying pavers, it tells you how much the base layer should slope. If you're building a deck, it tells you how much the frame should be lower at the outer end.

The slope should run in one direction only—away from the house. Do not slope toward the sides or create a crown (high point in the middle). A single direction is easier to build, easier to measure, and moves water faster than a crown does.

Measuring slope while you build

Use a 4-foot level and a tape measure to check your slope as you work. Place the level on the surface, with one end toward the house and one end pointing away. Slide a shim or spacer under the house-side end until the bubble sits in the center. Measure the thickness of the shim. For every 12 inches of level length, the shim should be 1/8 inch thick.

If your level is 4 feet long, the shim should be 1/2 inch thick (4 feet ÷ 12 inches × 1/8 inch = 1/2 inch). If your level is 6 feet long, the shim should be 3/4 inch thick. If your level is 8 feet long, the shim should be 1 inch thick.

Check the slope in multiple spots across the patio—near the house, in the middle, and at the far edge. The bubble should sit in the same position each time if your slope is consistent. Concrete and pavers can settle unevenly over time, so check again a few weeks after installation.

Why steeper slopes cause problems

A slope steeper than 1/4 inch per foot (twice the standard) drains water faster but becomes uncomfortable to walk on. Furniture slides downhill. Wheelchairs and walkers are harder to push. The patio looks visibly tilted, which is distracting even if you don't consciously notice why.

Very steep slopes—1/2 inch per foot or more—can cause tripping hazards and make the patio feel unsafe. They're also harder to build accurately because small mistakes in the base layer become visible in the finished surface.

If you have a very large patio (more than 30 feet wide), you might be tempted to use a steeper slope to avoid a total drop that seems too large. Instead, break the patio into sections with a low ridge or swale between them, and slope each section separately at the standard 1/8 inch per foot.

What happens if your slope is too shallow

A slope shallower than 1/8 inch per foot drains slowly. Water sits in low spots for hours or days after rain. Algae and moss grow in these wet areas. The surface becomes slippery. Concrete cracks from freeze-thaw cycles because water trapped in small pores expands when it freezes.

If your existing patio has shallow slope and water pools in certain spots, you have two options. The first is to add a French drain—a trench filled with gravel and perforated pipe that runs along the low spots and carries water away. The second is to regrade the soil around the patio so water flows away naturally, though this is labor-intensive if the patio is already installed.

Slope direction and drainage systems

Always slope away from the house. Water that runs toward the house can seep into the foundation, basement, or crawl space. If your patio is on the uphill side of your house, slope it away from the house and also away from the uphill direction so water doesn't collect between the house and the patio.

Where the water goes after it leaves the patio depends on your soil and local drainage. In most cases, water soaks into the surrounding soil naturally. If your soil is clay or compacted, water may pool at the patio edge. In that case, install a French drain or a surface drain (a sunken catch basin with a grate) at the low point, and run a pipe to daylight or to a rain garden.

Check your local building code before you install a drain system. Some areas require that drainage be directed to a storm sewer or a specific location on your property.

Slope for different patio materials

The 1/8 inch per foot rule applies to all patio surfaces, but the way you achieve it varies. For concrete, you slope the subbase (the compacted gravel layer) and the concrete forms before you pour. For pavers, you slope the sand base layer. For stone, you slope the gravel base and set each stone with a slight tilt. For composite decking, you slope the frame or the posts.

Concrete is the easiest to slope accurately because you can adjust the forms before pouring. Pavers are slightly harder because the sand base can shift during installation. Stone is hardest because each piece is irregular and must be set individually. If you're laying stone, use a level frequently and adjust the base layer under each stone as needed.

Permeable pavers (pavers with gaps for water to drain through) still need slope. The slope moves water away from the house; the gaps allow water to soak into the base layer below. Without slope, water pools on top of the pavers even if they're permeable.

Frequently Asked Questions

Can I slope my patio toward the sides instead of away from the house?

You can, but it's not ideal. Sloping toward the sides means water runs off the edges, which can erode the soil next to the patio and create muddy spots. Sloping away from the house directs water to a larger area where it soaks in more evenly. If you must slope toward the sides, also slope away from the house at the same time by creating a gentle ridge running parallel to the house.

What if my patio is attached to a deck—do I slope the deck too?

Yes. A deck should slope at 1/8 inch per foot away from the house, just like a patio. The deck boards should be spaced slightly apart (usually 1/8 inch) so water drains through the gaps and doesn't pool on the surface. If your deck is very large, you may need to slope it in sections.

How do I slope a patio if the ground is already sloped?

Measure the existing slope of the ground, then add the patio slope on top of it. If the ground already slopes away from the house at 1/8 inch per foot, your patio only needs to be level. If the ground slopes toward the house, your patio needs to slope away at more than 1/8 inch per foot to overcome the ground slope. Use a level and tape measure to find the ground slope before you build.

Is 1/8 inch per foot the same as a 1% slope?

No. One percent slope is 1/100 of the horizontal distance, which is shallower than 1/8 inch per foot. The 1/8 inch per foot rule (also written as 1:96) is steeper and drains better. Some building codes specify 1% slope for certain applications, so check your local code before you build.

Can I use a self-leveling concrete to create slope?

Self-leveling concrete finds its own level, so it won't create slope on its own. You must slope the subbase or the forms before pouring, then use self-leveling concrete on top. The concrete will settle into the slope you've created but won't add to it or reduce it.