How to Grade for a Patio So Water Drains Away

A new patio that holds a puddle against the back door after every storm is one of the most common callbacks I get. The pavers or concrete are usually fine. The problem is that nobody set the grade before the base went in, so water had nowhere to go but toward the house.

If you plan to grade for a patio yourself, the work is mostly measuring and patience. You need the right slope, a solid subgrade and a plan for where the water ends up. Here is how I lay one out on a typical backyard job.

How much slope a patio needs

The working number for most patios is a fall of 1/4 inch per foot away from the house. That is about a 2 percent slope. On a 12 foot deep patio, the far edge should sit 3 inches lower than the edge against the foundation.

Some installers go as low as 1/8 inch per foot on smooth concrete. I do not recommend it for pavers or stone, because joints and small settlement eat up that slope fast. Going steeper than 1/2 inch per foot makes chairs and tables feel tilted, so stay between 1/4 and 3/8 inch.

The patio surface also has to sit below the door threshold. Most codes and manufacturers want at least 1 inch below the sill for a covered door, and closer to 4 inches below siding or weep holes on brick. Check this first, because it sets your starting elevation.

Check the ground around the patio first

A patio is only as dry as the yard around it. Before you dig, walk the area during or right after a heavy rain and watch where water moves. If the lawn already slopes toward the house, grading just the patio area will not fix it. You will need to correct the surrounding grade, which we cover in our guide to grading a lot so water moves away from the foundation.

Also locate utilities. Call 811 at least a few working days before you dig. Gas and irrigation lines are often only 12 to 18 inches deep in backyards, which is right inside the depth you will excavate.

How to grade for a patio, step by step

For a 12 by 16 foot paver patio, plan on a full weekend with a rented plate compactor. A sod cutter saves a lot of shoveling if there is lawn.

1. Set your string lines

Drive stakes about 1 foot outside each corner. Run a mason's line along the house side at the finished patio height, using a line level to get it dead level. Then run lines out from the house and lower them by the fall you need. For 12 feet at 1/4 inch per foot, the far stakes get marked 3 inches below the house side.

2. Figure your excavation depth

A typical paver patio needs about 4 inches of compacted gravel base, 1 inch of bedding sand and the paver thickness, often 2 3/8 inches. That totals around 7 1/2 inches below finished height. On clay soil or in a freeze zone, increase the base to 6 inches. For a concrete slab, plan 4 inches of base plus a 4 inch slab.

3. Dig parallel to the strings

Measure down from the string every few feet as you dig, not from the existing ground. The ground lies to you. The string does not. Excavate 6 to 12 inches wider than the patio on each side so the base extends past the edge restraint.

4. Compact the subgrade

Run the plate compactor over the bare soil before any gravel goes in. Soft spots will show up as low areas or bounce under the plate. Dig those out and fill with gravel. If you hit a lot of soft fill or old topsoil, strip it, since organic soil keeps settling for years.

5. Add base in lifts

Place gravel in lifts of no more than 2 to 3 inches and compact each one. Lightly wet the gravel, since slightly damp material packs tighter than dry. Check your slope against the strings after every lift. Fixing a low spot at the base is easy. Fixing it under pavers is not.

Where the water goes after it leaves the patio

Sloping the patio only moves water to its edge. You still need somewhere for it to go. On a gentle lot, a lawn area that keeps falling away at 2 percent or more is usually enough. On a flat lot, you may need a shallow swale along the low edge to carry water to the side yard. Our article on how to build a drainage swale that works covers sizing and lining.

If downspouts empty onto or next to the patio, extend them past it or tie them into a buried line. A single downspout from a 600 square foot roof section can drop over 350 gallons in a 1 inch rain.

Why a perfectly flat patio is not the goal

Homeowners often ask for a patio that is "completely level" so furniture sits flat, and some installers will build one to keep the customer happy. I push back on that every time.

A level surface has no way to shed water. Rain sits on it, soaks into joints, washes out the bedding sand and freezes in winter. Within two or three seasons, pavers begin to heave and the low spots get deeper. At 1/4 inch per foot, the slope is nearly invisible when you are standing on it, and nobody has ever spilled a drink because of it.

The other request I decline is sloping the patio toward the house to meet a door that sits too low. If the threshold leaves no room for slope, the honest fix is a trench drain along the house side or a step down from the door, not a reverse slope.

Frequently asked questions

How much slope does a paver patio need?

Most paver patios need 1/4 inch of fall per foot away from the house, about 2 percent. That works out to 3 inches over 12 feet. Going steeper than 1/2 inch per foot makes furniture feel unsteady.

Can I build a patio on dirt without gravel?

You can set pavers directly on compacted soil, but they will settle and shift unevenly within a few years. A compacted gravel base drains water and spreads loads evenly. For anything more than a small path, a 4 to 6 inch gravel base is worth it.

How deep should I dig for a patio?

For a typical paver patio, dig about 7 to 9 inches below finished height to fit the gravel base, bedding sand and pavers. On clay or in cold climates, go deeper to allow a 6 inch base. Always measure from a string line set at your planned slope rather than from the existing ground.